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Chemical diversity - Highlighting a species richness and ecosystem function disconnect
Oikos
Abstract
The lack of predictability in litter-mix studies may result from the low correlation between species number and the traits that drive the processes under observation. From the standpoint of litter-quality-dependent ecological processes, we propose that litter chemical qualities are functional traits and introduce a multivariate index of chemical diversity (CDQ) based on Rao's quadratic entropy to describe the compositional heterogeneity of litter and foliar mixtures. Using published data from temperate and tropical forest systems to illustrate the relationship between species richness and chemical diversity, we show the variation of chemical diversity based on profiles of total nutrient concentrations (N, P, K, Ca and Mg) with species richness. We discuss how this behavior may explain the idiosyncratic responses exhibited in litter-mix experiments and how it may contribute to the observed dominance of species identity over species diversity. As a summary of resource heterogeneity relevant to detritivore and microbial processes, the chemical diversity index is potentially a better predictor of diversity effects on nutrient dynamics than species richness. Finally, we propose the use of infrared spectroscopy techniques for a rapid and more comprehensive determination of foliar and litter chemical composition to provide a more information-rich index.
... To know the role of genes and metabolites in determining the disease severity based on host immunological background, we calculated the Disease Severity Index (D) considering three different parameters separately, i.e., altered genes and metabolites meta-metabolites expressions [25]. ...
... The highest dissimilarity coefficient on 7-15 over 15-0 indicated a vast transition in meta-metabolite composition between day 7 and day 15 of the treatment condition ( Fig 3B). To investigate the role of significantly altered genes and metabolites in disease severity, we calculated the disease severity index considering the factor altered genes and metabolites in different treatment conditions [25]. Unlike the dissimilarity coefficient, the role of host metabolites was highest in disease severity index in C57BL/6 on day 15-0 over 0-7 (Fig 3C). ...
... Increased Dissimilarity Coefficient between different clusters indicated more intense differential respond between different treatment conditions. With increased dissimilarity between clusters, both the strains' disease severity index was also increased [25]. The genes, metabolites, and meta-metabolites involved in the higher disease severity index were mainly related to the activation of the pro-inflammatory responses in the host. ...
The health and economic burden of colitis is increasing globally. Understanding the role of host genetics and metagenomics is essential to establish the molecular basis of colitis pathogenesis. In the present study, we have used a common composite dose of DSS to compare the differential disease severity response in C57BL/6 (Th1 biased) and BALB/c (Th2 biased) mice with zero mortality rates. We employed multi-omics approaches and developed a newer vector analysis approach to understand the molecular basis of the disease pathogenesis. In the current report, comparative transcriptomics, metabonomics, and metagenomics analyses revealed that the Th1 background of C57BL/6 induced intense inflammatory responses throughout the treatment period. On the contrary, the Th2 background of BALB/c resisted severe inflammatory responses by modulating the host’s inflammatory, metabolic, and gut microbial profile. The multi-omics approach also helped us discover some unique metabolic and microbial markers associated with the disease severity. These biomarkers could be used in diagnostics.
... To know the role of genes and metabolites in determining the disease severity based on host immunological background, we calculated the Disease Severity Index (D) considering three different parameters separately, i.e., altered genes and metabolites meta-metabolites expressions [25]. ...
... The highest dissimilarity coefficient on 7-15 over 15-0 indicated a vast transition in meta-metabolite composition between day 7 and day 15 of the treatment condition ( Fig 3B). To investigate the role of significantly altered genes and metabolites in disease severity, we calculated the disease severity index considering the factor altered genes and metabolites in different treatment conditions [25]. Unlike the dissimilarity coefficient, the role of host metabolites was highest in disease severity index in C57BL/6 on day 15-0 over 0-7 (Fig 3C). ...
... Increased Dissimilarity Coefficient between different clusters indicated more intense differential respond between different treatment conditions. With increased dissimilarity between clusters, both the strains' disease severity index was also increased [25]. The genes, metabolites, and meta-metabolites involved in the higher disease severity index were mainly related to the activation of the pro-inflammatory responses in the host. ...
The health and economic burden of colitis is increasing globally. Understanding the role of host genetics and metagenomics is essential to establish the molecular basis of colitis pathogenesis. In the present study, we have used a common composite dose of DSS to compare the differential disease severity response in C57BL/6 (Th1 biased) and BALB/c (Th2 biased) mice with zero mortality rates. We employed multi-omics approaches and developed a newer vector analysis approach to understand the molecular basis of the disease pathogenesis. In the current report, comparative transcriptomics, metabonomics, and metagenomics analyses revealed that the Th1 background of C57BL/6 induced intense inflammatory responses throughout the treatment period. On the contrary, the Th2 background of BALB/c resisted severe inflammatory responses by modulating the host’s inflammatory, metabolic, and gut microbial profile. The multi-omics approach also helped us discover some unique metabolic and microbial markers associated with the disease severity. These biomarkers could be used in diagnostics.
... However, functional identity and functional diversity are not mutually exclusive in affecting ecosystem processes (Violle et al. 2007) such as primary productivity (Schumacher and Roscher 2009;Roscher et al. 2012) or litter decomposition (Mokany et al. 2008;Barantal et al. 2011;Handa et al. 2014). Although these functional trait-based approaches have primarily been developed at the level of the plant community, several studies showed that they can be also useful in the understanding of diversity effects on litter decomposition (Epps et al. 2007;Bowman 2008, 2010) or other soil processes Bowman 2008, 2010). ...
... From these measurements we calculated specific root length (SRL, m g -1 , as the ratio L/RDM), root tissue density (RTD, g cm -3 , as the ratio of RDM/V), root thickness (RTh, cm 3 m -1 , as the ratio V/L), and finally, root length per soil volume (L/Volume, cm cm -3 , as the ratio L/soil volume).The community-weighted mean traits (CWM) of fine roots (SRL CWM , RTD CWM , RTh CWM , L/volume CWM , and Diam CWM ) were calculated as the average trait values of morphological traits following:Trait CWM = ∑ × =1, where is the relative abundance for species i (50% for each species in rhizotrons with two species), and is the trait value for species i. The functional dissimilarity of traits in rhizotrons with two species was calculated according to Rao's quadratic entropy(Epps et al. 2007) for each rhizotron (SRL FD , RTD FD , RTh FD , L/Volume FD , Diam FD and the global trait dissimilarity All FD ) as:Trait FD = ∑ ...
... MicroResp™,), a functional assessment of the impact of the interaction between diversity and reduced precipitation is currently lacking.Here, we assessed how experimentally reduced precipitation in a Mediterranean shrubland ecosystem affects the functioning of soil microbial community along a natural gradient of plant diversity (one to four woody plant species). We hypothesized that i) an increase in litter species richness and functional dissimilarity (Rao's quadratic entropy; Botta-Dukát 2005;Epps et al. 2007) will lead to more complementary microbial communities that are able to degrade multiple substrates more efficiently, and ii) the soil microbial communities associated to more diverse litter mixtures are also more resistant to reduced precipitation. To test our hypotheses, we characterized the ability of soil microbial communities to respire on 15 different C substrates and to decompose cellulose paper in the soil associated to all possible combinations of litter mixtures of four woody shrub species (Cistus albidus L., Quercus coccifera L., Rosmarinus officinalis L. and Ulex parviflorus Pourr.) ...
Longer drought periods and/or overall less precipitation are thought to be major consequences of ongoing climate change in the Mediterranean region. These changes in the water regime will likely affect community composition, biodiversity and ecosystem processes, but very little is known about how biodiversity and changes in precipitation interactively affect ecosystem functioning. In my PhD thesis, I aimed to quantify the role of plant diversity in the response of Mediterranean shrubland ecosystem to a decrease in water availability, with a particular interest in belowground processes, such as soil microbial community functioning and functional responses in plant roots.
I used a rhizotron approach under partially controlled conditions to study plant growth responses to repetitive severe droughts, with a particular focus on root growth. Two individuals of the same species or in all possible combinations of the three dominating species at our field site (Quercus coccifera, Cistus albidus, Brachypodium retusum) were grown together in a rhizotron. Repetitive severe droughts had a negative effect on survival of the two woody species (Q. coccifera, C. albidus), but not of the grass B. retusum. Interspecific competition generally increased survival of C. albidus and B. retusum compared to monospecific competition. Conversely, interspecific competition decreased the survival of Q. coccifera. Likewise, I found that root morphological traits were mostly affected by the neighbor species identity rather than by severe drought. The community level physiological profiles (CLPPs) of root associated soil microbial communities did not differ between drought treatments and were also not affected by plant species identity. However, CLPPs changed towards more total microbial activities but less diverse resource use at increasing soil depth. Collectively these results suggest that plant species composition of the studied Mediterranean shrubland has a stronger effect on growth, intraspecific variability in root traits and survival than repetitive severe droughts.
In the context of a larger collaborative project (CLIMED), I used a natural gradient of shrub species diversity in a Mediterranean shrubland ecosystem (garrigue) to which a permanent partial rain exclusion treatment (12% less precipitation) was added. This field experiment allowed me to study the responses of soil microbial community level physiological profiles (CLPPs) to reduced precipitation and to a change plant-produced leaf litter material decomposing on the ground as a key resource for heterotrophic soil microorganisms over two years. While rain exclusion had only a minor impact on the diversity of substrates metabolized by the microbial communities, litter species richness promoted global soil microbial activity by increased catabolic diversity of the soil microbial community. These results suggest that indirect climate change effects on plant species composition and richness might have more important consequences for soil microbial functioning than reduced precipitation in the studied Mediterranean shrubland ecosystem.
Both, the field study of soil microbial functioning and the rhizotron study of plant growth and survival clearly showed that plant species identity and diversity may be more important for the functioning of these Mediterranean shrublands than increased drought. I conclude that climate change induced shifts in plant species composition and diversity may have more important consequences for the functioning of Mediterranean shrublands than the direct effects of altered precipitation.
... However, functional identity and functional diversity are not mutually exclusive in affecting ecosystem processes (Violle et al. 2007) such as primary productivity (Schumacher and Roscher 2009;Roscher et al. 2012) or litter decomposition (Mokany et al. 2008;Barantal et al. 2011;Handa et al. 2014). Although these functional trait-based approaches have primarily been developed at the level of the plant community, several studies showed that they can be also useful in the understanding of diversity effects on litter decomposition (Epps et al. 2007;Bowman 2008, 2010) or other soil processes Bowman 2008, 2010). ...
... where -. is the relative abundance for species i (50% for each species in rhizotrons with two species), and +034+ . is the trait value for species i. The functional dissimilarity of traits in rhizotrons with two species was calculated according to Rao's quadratic entropy(Epps et al. 2007) for each rhizotron (SRL FD , RTD FD , RTh FD , L/Volume FD , Diam FD and the global trait dissimilarity All FD ) as:Trait FD = , , 7478 9 :48 ; <6& ; >6& ...
... MicroResp™, Chapman et al. 2007; Campbell et al. 2008), a functional assessment of the impact of the interaction between diversity and reduced precipitation is currently lacking.Here, we assessed how experimentally reduced precipitation in a Mediterranean shrubland ecosystem affects the functioning of soil microbial community along a natural gradient of plant diversity (one to four woody plant species). We hypothesized that i) an increase in litter species richness and functional dissimilarity (Rao's quadratic entropy; Botta-Dukát 2005;Epps et al. 2007) will lead to more complementary microbial communities that are able to degrade multiple substrates more efficiently, and ii) the soil microbial communities associated to more diverse litter mixtures are also more resistant to reduced precipitation. To test our hypotheses, we characterized the ability of soil microbial communities to respire on 15 different C substrates and to decompose cellulose paper in the soil associated to all possible combinations of litter mixtures of four woody shrub species (Cistus albidus L., Quercus coccifera L., Rosmarinus officinalis L. and Ulex parviflorus Pourr.) ...
Les modèles disponibles prévoient que le changement climatique entrainera de plus longues périodes de sécheresse et/ou une diminution globale des précipitations en région méditerranéenne. Ces changements affecteront probablement la composition des communautés, la biodiversité et les processus écosystémiques. Cependant, les effets de la biodiversité, des changements de précipitations et de leurs interactions sur le fonctionnement des écosystèmes restent mal connus. Dans cette thèse, j’ai cherché à quantifier le rôle de la diversité des plantes dans la réponse d’un écosystème de garrigue méditerranéenne à une diminution de la disponibilité en eau, avec un intérêt particulier pour les processus souterrains, tels que le fonctionnement de la communauté microbienne du sol et les réponses fonctionnelles des racines.Afin d’étudier les conséquences d’une sécheresse sévère répétée sur la croissance végétale, et particulièrement racinaire, j’ai mis en place une expérience en rhizotrons, en conditions semi-contrôlées. Dans chaque rhizotron ont été plantées deux individus d’une même ou de différentes espèces des trois espèces dominantes de notre site d’étude (Quercus coccifera, Cistus albidus, Brachypodium retusum). Les sécheresses sévères répétées ont eu un effet négatif sur la survie des deux espèces ligneuses mais pas sur celle de l’herbacée. La compétition interspécifique a généralement augmenté la survie de C. albidus et B. retusum comparé à la compétition intraspécifique. A l’inverse, la compétition interspécifique a diminué la survie de Q. coccifera. De la même manière, les traits morphologiques racinaires ont été plus affectés par l’identité des espèces voisines que par le traitement de sécheresse. Les profils métaboliques des communautés microbiennes (CLPP) de sol associé aux racines n’ont pas été affectés par les traitements de sécheresse ni par l’identité des espèces végétales. Cependant, avec l’augmentation de la profondeur du sol, les CLPP ont augmentés mais avec une utilisation de ressources moins diversifiées. Ces résultats suggèrent que la composition d’espèces végétales de la garrigue méditerranéenne étudiée a un effet plus important sur la croissance, la variabilité intraspécifique des traits racinaires et la survie que les sécheresses sévères répétées.Dans le contexte d’un projet collaboratif (CLIMED), j’ai utilisé un gradient naturel de diversité d’espèces d’arbustes d’un écosystème de garrigue méditerranéenne ayant reçu un traitement d’exclusion de pluie partielle (-12% de précipitation). Cette expérience m’a permis d’étudier les réponses des profils métaboliques des communautés microbiennes du sol CLPP à une diminution des précipitations ainsi qu’à un changement de diversité des litières végétales décomposant au sol comme ressource clé pour les microorganismes hétérotrophiques du sol, pendant deux ans. Alors que l’exclusion de pluie n’a eu qu’un impact mineur sur la diversité des substrats métabolisés par les communautés microbiennes, la richesse spécifique de la litière a favorisé l’activité microbienne du sol en augmentant la diversité catabolique de la communauté microbienne du sol. Ces résultats suggèrent que les effets indirects du changement climatique sur la composition et la richesse des espèces végétales pourraient avoir des conséquences plus importantes pour le fonctionnement microbien du sol que la réduction des précipitations prévue dans l’écosystème de garrigue méditerranéenne étudié.Mes deux études, de terrain et en rhizotron, ont clairement montrées que l’identité et la diversité des espèces végétales peuvent être plus importantes pour le fonctionnement de ces garrigues méditerranéennes qu’une augmentation des sécheresses. Je conclus que les changements de composition et de diversité d’espèces végétales induits par le changement climatique peuvent avoir des conséquences plus importantes pour le fonctionnement des garrigues méditerranéennes que les effets directs d’une modification des précipitations
... What's more, species "richness" and "composition" are often used as the index of "diversity" in previous studies, but their influences on decomposition processes are also intimately related to the chemical traits of litters included in the mixture (Ball et al., 2008;Jiang et al., 2013). Therefore, litter chemistry is considered to be an effective way to examine litter-mixing effects (Epps et al., 2007;Lecerf et al., 2011). Litter chemical traits, such as lignin, total phenol, soluble sugar and nutrients (e.g., N, P, K, Fe, etc.), have been reported in affecting litter decomposition (Madritch and Hunter, 2004;Mungai and Motavalli, 2006;Bonanomi et al., 2010;Meier and Bowman, 2010). ...
... These chemical components released from plant litter may affect the production and activity of microbes, which ultimately influence the decomposition process positively or negatively (Sinsabaugh et al., 2002). Following the recent studies on mixed litter decomposition, littermixing effects might due to chemical traits diversity (i.e., the dissimilarity of chemical traits) among the constituent litter species (Epps et al., 2007;Lecerf et al., 2011). However, some other studies reported the opposite (Frainer et al., 2015). ...
... As there is lack of consensus on how "diversity" should be measured, it is necessary to adopt several diversity indices and determine which one performs best in the research (Petchey and Gaston, 2006). Following previous studies, six litter chemical diversity indices were used in this work, i.e., FAD2, MFAD, FD, FD Q , FRic and FDis (Table S2), based on the chemical traits we measured (Petchey and Gaston, 2006;Epps et al., 2007;Mouchet et al., 2010;Lecerf et al., 2011). These six indices characterized two facets of chemical diversity: FAD2, MFAD, FD and FRic characterized the component of "richness" in chemical diversity, FD Q and FDis characterized the component of "divergence" in diversity (Mouchet et al., 2010). ...
The mechanisms of litter-mixing effects on soil carbon (C) and nitrogen (N) cycling in alpine ecosystems remain inconclusive. In this study, we employed a four-month litter-mixing experiment to examine the relationship between litter chemical diversity, incubation time and litter-mixing effects on soil C and N fluxes from an alpine steppe ecosystem in Northern Tibet. Litter mixtures caused predominantly non-additive effects on soil C and N fluxes, with more synergistic effects for carbon dioxide (CO 2)/nitrous oxide (N 2 O) emissions while more antagonistic effects for soluble organic C (SOC), total inorganic N (TIN), microbial biomass C (MBC) and urease activity (UA). Litter-mixture would largely increase the fluxes of CO 2 , N 2 O emission and SON, while decrease SOC, TIN, MBC and UA concentration. We calculated six chemical diversity indices, and found litter chemical diversity correlated with the strength of litter-mixing effect on soil C and N, but the indices we chose may be influenced our understanding of the relationship. Our results also showed that models including the chemical diversity indices and incubation time generally gave better explanation on variations of litter-mixing effects. This work demonstrated a general relationship between litter chemical diversity and non-additive responses of soil C and N cycling, and suggested that incubation time is an important factor in understanding the litter-mixing effects.
... However, functional identity and functional diversity are not mutually exclusive in affecting ecosystem processes (Violle et al. 2007) such as primary productivity (Schumacher and Roscher 2009;Roscher et al. 2012) or litter decomposition (Mokany et al. 2008;Barantal et al. 2011;Handa et al. 2014). Although these functional traitbased approaches have primarily been developed at the level of the plant community, several studies showed that they can be also useful in the understanding of diversity effects on litter decomposition (Epps et al. 2007;Bowman 2008, 2010) or other soil processes Bowman 2008, 2010). ...
... Here, we assessed how experimentally reduced precipitation in a Mediterranean shrubland ecosystem affected the functioning of soil microbial community along a natural gradient of plant diversity (one to four woody plant species). We hypothesized that (i) an increase in litter species richness and functional dissimilarity (Rao's quadratic entropy; Botta-Dukát 2005; Epps et al. 2007) will lead to more complementary microbial communities that are able to degrade multiple substrates more efficiently and (ii) the soil microbial communities associated to more diverse litter mixtures are also more resistant to reduced precipitation. To test our hypotheses, we characterized the ability of soil microbial communities to respire on 15 different C substrates and to decompose cellulose paper in the soil associated to all possible combinations of litter mixtures of four woody shrub species (Cistus albidus, Quercus coccifera, Rosmarinus officinalis, and Ulex parviflorus) dominating at our study site, in a fully factorial rainfall exclusion experiment, and after 1 and 2 years of in situ decomposition. ...
... where B i is the relative abundance for species i and trait i is the trait value for species i. The functional dissimilarity was calculated according to the Rao index (Epps et al. 2007) for each litter mixture (C FD , N FD , P FD , Phenolics FD , Lignin FD , Lignin/N FD , DOC FD , TDN FD , and WHC FD ) as follows: ...
This study aimed at quantifying the consequences of reduced precipitation and plant diversity on soil microbial community functioning in a Mediterranean shrubland of southern France. Across a natural gradient of shrub species diversity, we established a total of 92 plots (4 × 4 m) with and without a moderate rain exclusion treatment of about 12 % of total precipitation. Shrub diversity included all possible combinations of the four dominant species (Cistus albidus, Quercus coccifera, Rosmarinus officinalis, and Ulex parviflorus). Respective leaf litter mixtures of these species combinations were exposed in all plots over 2 years. We quantified how litter species richness and the reduction in precipitation affected the soil microbial substrate utilization (measured by CO2 evolution using the MicroResp method) on soil samples collected underneath each individual litter mixture after 1 and 2 years of decomposition. Moderate precipitation reduction had a minor impact, but litter species richness and the dissimilarity in phenolic concentrations (estimated using Rao’s quadratic entropy) showed a positive effect on the diversity of substrates metabolized by the microbial communities. Moreover, litter species richness increased soil microbial activity by increasing the catabolic diversity of the soil microbial community. These effects were mostly driven by the presence of Quercus and Ulex leaf litter, which at the same time reduced microbial metabolic dominance, while the presence of Rosmarinus had opposite effects. Our data suggest that plant species loss can have stronger effects on the functioning of soil microbial communities than moderate drought, with potentially important feedbacks on biogeochemical cycling in Mediterranean shrubland ecosystems.
... Proximately, this inconsistency is due to the pervasive experimental bias towards simplified, single-trophic ecosystems (e.g., grasslands), whereas the effects of diversity on more complex, multitrophic ecosystems remains understudied (Duffy 2002, Striebel et al. 2012, Jabiol et al. 2013, Lefcheck et al. 2015. Fundamentally, there is still much debate over which measures of diversity most strongly correlate with function (McGill et al. 2006, Epps et al. 2007, Villéger et al. 2008, Lecerf et al. 2011). In addition, mechanisms underlying diversity-function relationships are often inferred, yet rarely tested (Cardinale et al. 2011), and debate over measurement of diversity has only widened this gap in our knowledge. ...
... Testing these mechanisms by manipulating trait diversity has proven challenging. Often, more than one phenotypic trait is responsible for functional responses, yet simultaneously controlling and manipulating the diversity of multiple traits is mathematically and logistically difficult (Epps et al. 2007). Consequently, many studies have only explicitly manipulated single traits (e.g., Schindler and Gessner 2009). ...
... We assessed lignin and soluble carbon via a modified carbon fractionation method (Moorhead and Reynolds 1993, see details on this method in Appendix S1). All measured chemical components are widely used in forestry studies and many of them have known correlations with litter decomposition rate (Epps et al. 2007) ...
Research suggests that a positive relationship exists between diversity and ecological function, yet the multi-trophic effects of biodiversity remain poorly understood. The resource complementarity hypothesis suggests that increasing the trait diversity of resources provides a more complete diet for consumers, elevating consumer feeding rates. Whereas previous tests of this mechanism have measured trait diversity as the variation of single traits or the richness of functional groups, we employed a multivariate trait index to manipulate the chemical diversity of temperate tree litter species in outdoor pond mesocosms. We inoculated outdoor mesocosms with diverse and multi-trophic communities of microbial and macro-consumer species that rely on leaf litter for energy and nutrients. Litter was provided at three levels of chemical trait diversity, a constant level of species richness, and an equal representation of all litter species. Over three months, we measured more than 65 responses, and assessed the effects of litter chemical diversity and chemical trait means (i.e., community-weighted means). We found that litter chemical diversity positively correlated with decomposition rate of leaf litter, but had no effect on biomass or density of producers and consumers. However, the pond communities often responded to chemical trait means, particularly those related to nutrients, structure, and defense. Our results suggest that resource complementarity does have some effect on the release of energy and nutrients from decomposing substrates in forest ponds, but does not have multi-trophic effects. Our results further suggest that loss of tree biodiversity could affect forest ecosystem functionality, and particularly the processes occurring in and around ponds and wetlands.
... Understanding the effects of litter on temperate forest aquatic communities and predicting the response of these communities to the chemistry of individual litter species has proven challenging. Although it is generally true that biomass production on or around nutrientrich and labile litter species is greater than production around nutrient-poor litter (Yanoviak 1999, Motomori et al. 2001, Swan and Palmer 2006, single litter species consist of both beneficial and harmful chemical compounds that can influence biotic growth and fitness in contrasting ways (Wardle et al. 1997, Epps et al. 2007). In particular, acidic and structural compounds (e.g., phenolics and lignins, respectively) often remain in the litter after senescence and can inhibit microbial growth and activity, regardless of nutrient content (Webster and Benfield 1986, Hoorens et al. 2002, Ardón and Pringle 2008. ...
... An alternative explanation is that unmeasured traits may exert some control during later stages. Although multiple other components of litter chemistry have occasionally been published as important drivers of ecological function (Epps et al. 2007), the broad traits that we used are the most often cited determinants of litter palatability and quality (Taylor et al. 1989;Ardón and Pringle 2008). Our study demonstrates the usefulness of these traits in determining multi-trophic community composition and productivity. ...
... This result is important given the growing acceptance that litter quality can influence function as much as or more than litter quantity. Measuring quality is not straightforward, as litter species are complex combinations of multiple chemical factors (Epps et al. 2007). ...
The composition of species is continually shifting due to natural succession, disturbance, and human influences. Predicting effects of these changes requires understanding species interactions, phenotypic traits responsible these interaction, and general relationships between diversity and ecological processes. In this thesis, I explore how changes in temperate forest tree composition alter processes within forest wetland ecosystems, the chemical traits of litter responsible for these effects, and general relationships between litter diversity and ecological processes.
Forest wetlands often receive massive amounts of tree leaf litter, and contain diverse food webs that recycle energy and nutrients within litter into myriad inorganic and organic forms. In the first study, I hypothesized that the abiotic and biological components of forest wetlands respond to changes in the input of tree leaf litter species. I provided different litter species to wetland communities in outdoor mesocosms, using ten common deciduous tree litter species. Effects were dramatic, including variation in the biomass, density, and survival of consumers. In this study, I also demonstrate that several traits of litter explain much of the variation in these effects. In the second study, I hypothesized that variation in litter inputs also induce phenotypic changes in consumer development and morphology. Using wood frogs as a model species, I found that variation in litter species alters development rate and several morphological features, such as tail length, mouth size, and gut length. In the third study, I hypothesized that variation in litter inputs alters predator-prey interactions by changing the chemical and physical structure of wetland ecosystems. The results of this study suggest that interactions between litter resources and top-down interactions should be considered to accurately predict the consequences of shifting litter species composition. In the final study, I hypothesized that a general, positive relationship exists between litter chemical trait diversity and wetland consumer biomass. I found strong effects of trait diversity on decomposition rate, but no effects across a diverse array of consumer species. This suggests that wetland communities – although responsive to changes in single litter species chemistry – respond positively to increased litter species richness and may be resistant to fluctuations of litter chemical diversity.
... Nonadditive effects may be due to leaf litter chemical characteristics, such as compounds which translocate from one leaf species and may enhance (e.g., nitrogen) or inhibit (e.g., polyphenols) decomposition of other species (Lummer et al., 2012;Sanpera-Calbet et al., 2009;Schimel & Hättenschwiler, 2007). Nonadditive effects may also be due to leaf litter physical characteristics, such as higher leaf toughness of one species, which may act as an armoring effect against physical abrasion, thus decreasing decomposition of other more fragile species Wardle et al., 1997), and synergistic effects may also arise from the higher habitat/resource heterogeneity of mixtures when compared to single species (Epps et al., 2007), which enhances colonization by biota and eventually results in higher overall processing rates by leaf consumers (Bastian et al., 2008). ...
... The number of species in a mixture may not be a good predictor of litter-quality-dependent processes and the inclusion of another species may even contribute to the homogenization of the substrate (Epps et al., 2007). Moreover, functional diversity has been considered a better predictor than species diversity (e.g., Bonanomi et al., 2014;Grossman et al., 2020), and highest functional diversity has been found in mixtures of species with contrasting N-concentrations and C:N ratio (Santonja et al., 2020), ...
The effect of mixing litter on decomposition has received considerable attention in terrestrial and aquatic (but rarely in both) ecosystems, with a striking lack of consensus in the obtained results. We studied the decomposition of a mixture of poplar and alder in three terrestrial: aquatic exposures to determine (1) if the effect of mixing litter on mass loss, associated decomposers (fungal biomass, sporulation rates, and richness), and detritivores (abundance, biomass, and richness of invertebrate shred-ders) differs between the stream (fully aquatic exposure) and when litter is exposed to a period of terrestrial exposure prior to immersion and (2) the effect of the mixture across exposure scenarios. The effect of the mixture was additive on mass loss and synergistic on decomposers and detritivores across exposure scenarios. Within scenarios , mass loss and decomposers showed synergistic effects only in the fully aquatic exposure, detritivores showed synergistic effects only when the period of terrestrial was shorter than the period of aquatic exposure, and when the period of terrestrial was equal to the period of aquatic exposure the effect of the mixture was additive on mass loss, decomposers, and detritivores. The species-specific effects also differed among exposure scenarios. Alder affected poplar only when there was a period of terrestrial exposure, with increased sporulation rates and fungal richness in exposure 25:75, and increased mass loss in exposure 50:50. Poplar affected alder only under fully aquatic exposure, with increased mass loss. In conclusion, the synergistic effects of the mixture changed with a period of terrestrial exposure prior to immersion. These results provide a cross-boundary perspective on the effect of mixing litter, showing a legacy effect of exposure to terrestrial decomposition on the fate of plant litter in aquatic ecosystems and highlighting the importance of also assessing the effect of mixing litter on the associated biota and not only on mass loss. K E Y W O R D S cross-ecosystem flows of organic matter,
... Nonadditive effects may be due to leaf litter chemical characteristics, such as compounds which translocate from one leaf species and may enhance (e.g., nitrogen) or inhibit (e.g., polyphenols) decomposition of other species (Schimel & Hättenschwiler, 2007;Sanpera-Calbet et al., 2009;Lummer et al., 2012). Nonadditive effects may also be due to leaf litter physical characteristics, such as higher leaf toughness of one species which may act as an armouring effect against physical abrasion thus decreasing decomposition of other more fragile species (Wardle et al., 1997;Swan et al., 2008), and synergistic effects may also arise from the higher habitat/resource heterogeneity of mixtures when compared to single species (Epps et al., 2007), which enhances colonisation by biota and eventually results in higher overall processing rates by leaf consumers (Bastian et al., 2008). ...
... While the results, obtained for one mixture at one site, may not extrapolate a trend on a broader context, the mixture used here was the best combination to assess possible nonadditive effects. The number of species in a mixture may not be a good a predictor of litter-quality-dependent processes and the inclusion of another species may even contribute to the homogenization of the substrate (Epps et al., 2007). Moreover, functional diversity has been considered a better predictor than species diversity (e.g., Bonanomi et al. 2014;Grossman et al., 2020) and highest functional diversity has been found in mixtures of species with contrasting N-concentrations and C:N ratio (Santonja et al., 2020), which also more frequently show nonadditive synergistic interactions (Bonanomi et al. 2014). ...
The effect of mixing litter on decomposition has received considerable attention in terrestrial and aquatic (but rarely in both) ecosystems, with a striking lack of consensus in the obtained results. We studied the decomposition of a mixture of poplar and alder in three terrestrial:aquatic exposures to determine (1) if the effect of mixing litter on mass loss, associated decomposers and detritivores differs between the stream (fully aquatic exposure) and when litter is exposed to a period of terrestrial exposure prior to immersion and (2) the global effect of the mixture across exposure scenarios. The effect of the mixture was additive on mass loss and synergistic on decomposers and detritivores across exposure scenarios. Within scenarios, mass loss and decomposers showed synergistic effects only in the fully aquatic exposure, detritivores showed synergistic effects only when the period of terrestrial was shorter than the period of aquatic exposure, and when the period of terrestrial was equal to the period of aquatic exposure the effect of the mixture was additive on mass loss, decomposers, and detritivores. The species-specific effects also differed among exposure scenarios. Alder affected poplar only when there was a period of terrestrial exposure, with increased sporulation rates and fungal richness in exposure 25:75, and increased mass loss in exposure 50:50. Poplar affected alder only under fully aquatic exposure, with increased mass loss. In conclusion, the synergistic effects of the mixture changed with a period of terrestrial exposure prior to immersion. These results provide a cross-boundary perspective on the effect of mixing litter, showing a legacy effect of exposure to terrestrial decomposition on the fate of plant litter in aquatic ecosystems and highlighting the importance of assessing the effect of mixing litter on the associated biota and not only on mass loss.
... According to Grime's biomass ratio hypothesis (Grime 1998) species composition and diversity can influence process rates through their relative abundance or that of particular traits they represent. Diversity effects can additionally be driven by functional divergence or dissimilarity of their traits leading to non-additive diversity effects (Epps et al. 2007;Villéger et al. 2008). For the assessment of the relative importance of mean trait values and trait dissimilarity of leachate mixtures, we calculated the widely used community-weighted mean (CWM) trait values (Garnier et al. 2004) and Rao's quadratic entropy (Botta-Dukát 2005;Epps et al. 2007). ...
... Diversity effects can additionally be driven by functional divergence or dissimilarity of their traits leading to non-additive diversity effects (Epps et al. 2007;Villéger et al. 2008). For the assessment of the relative importance of mean trait values and trait dissimilarity of leachate mixtures, we calculated the widely used community-weighted mean (CWM) trait values (Garnier et al. 2004) and Rao's quadratic entropy (Botta-Dukát 2005;Epps et al. 2007). The communityweighted mean (CWM) traits of mixtures (m) were calculated as followed: ...
Leaching of water-soluble compounds is a dominant process during the first stages of litter decomposition, providing the microorganisms in the underlying soil with an important source of labile carbon and nutrients. Leachate composition (quantity and quality) can vary considerably among different plant species, but its consequences for soil microbially-driven processes remains largely unexplored. Here, we evaluated the differences in leachate quantity and quality from freshly fallen leaf litter of widely distributed coniferous and deciduous broadleaf tree species of European temperate forests, and their effects on soil microbial responses in a microcosm experiment under controlled conditions. Leachates of broadleaf litter contained higher amounts of carbon and nitrogen available for microbes, but with substantially higher aromaticity than leachates from coniferous litter. A one-time leachate addition to soils immediately increased soil microbial respiration with longer lasting effects of deciduous broadleaf compared to coniferous litter leachates leading to a microbial community with an apparently more efficient use of carbon. When leachates of different species were mixed, the observed microbial responses differed in some cases from that expected based on soils to which leachates from single species were added. These non-additive effects were partly explained by the functional dissimilarity of leachate traits, suggesting complementary resources for microorganisms when leachates of different species are available. Our data show that species-specific litter-derived leachates of varying quantity and quality and their mixtures distinctly affect soil microorganisms. In forest ecosystems with recurrent leaf litter inputs from the same species, such leachate effects may determine soil processes also in the longer term, controlling biogeochemical cycling to an important degree.
... Le maintien des processus de l'écosystème face à des stresseurs multiples dépend donc en partie de la tolérance des espèces constituant la communauté (Vinebrooke et al. 2004 (Naeem et Wright 2003). La distribution des traits fonctionnels au sein des communautés seraient ainsi un meilleur prédicteur des propriétés de l'écosystème que la diversité taxonomique (Epps et al. 2007) et devrait être plus systématiquement mesurée, y compris pour les consommateurs (champignons et macroinvertébrés) pour l'étude des relations entre biodiversité et décomposition (Gessner et al. 2010). S'affranchir de la diversité taxonomique offre un pouvoir d'extrapolation des résultats supérieur (Naeem et Wright 2003) puisque ceux-ci s'appliquent à n'importe quelles conditions environnementales, y compris lorsque leurs communautés sont contrastées en termes de diversité taxonomique. ...
... Ainsi une description de ces interactions, au sein d'un groupe trophique et entre différents groupes trophiques permettrait une meilleure interprétation des résultats observés lors d'expérimentations. Dans le cas des hyphomycètes aquatiques par exemple, si l'impact de divers facteurs abiotiquesGulis et Suberkropp 2004 ;Lecerf et Chauvet 2008) ou encore les effets de l'activité de différentes espèces fongiques sur la décomposition et les performances des macroinvertébrés détritivores ont été décrits(Suberkropp et al. 1983), les mécanismes structurant les communautés, et en particulier les interactions entre espèces ont été peu abordées (voirTreton et al. 2004).Finalement, l'utilisation d'une approche basée sur les traits fonctionnels, recemment développée pour l'étude des effets de la diversité des litières permet de s'affranchir de l'identité des espèces et semble prometteuse(Epps et al. 2007 ;Meier et Bowman 2008 ; Lecerf et al. in press). Par exemple,Lecerf et al (in press) en utilisant une mesure de la diversité fonctionnelleVilléger et al. 2008) ont déterminé que les effets de mélanges des litières sur la décomposition apparaissaient d'avantage lorsque des litières contrastées étaient utilisées, apportant ainsi une information importante pour l'interprétation de tels effets et démontrant que les effets de diversité des litières étaient plus prédictibles que considéré auparavant. ...
Evaluating the consequences of biodiversity loss on the functioning of various ecosystems has recently become a central focus of ecology. By means of 4 experiments carried out in headwater streams, we show that the diversity of the resource, of decomposers and their predators can alter decomposition process through different mechanisms. Notably we show that concomitant alterations of biodiversity at several trophic levels can have synergistic consequences on the functioning of such ecosystems and litter decomposition rates. These results suggest that taking into account the influence of trophic complexity on community structure and ecosystem functioning is necessary to evaluate formally the consequences of biodiversity loss at a global scale
... functional leaf traits) rather than from the taxonomic identity of the species. From a theoretical framework, Epps et al. (2007) argued that chemical diversity, more than species richness, was important in describing litter diversity and species interactions. Therefore, species mixtures composed of species having more strongly contrasting chemical or structural differences that affect decomposition rates (i.e. ...
... Therefore, species mixtures composed of species having more strongly contrasting chemical or structural differences that affect decomposition rates (i.e. mixtures having greater functional diversity) may be more likely to develop interactions (Heemsbergen et al. 2004, Epps et al. 2007). The degree of variation of functional diversity within mixtures could therefore be an important source of error in the prediction of mixture decomposition rates. ...
We tested the hypothesis that interactions between plant species during the process of mixed-species leaf litter decomposition increases with increasing functional diversity of leaves within the mixtures; specifically, there is a positive correlation between functional dispersion and the deviations from Grime's biomass-ratio hypothesis, with a null intercept. We measured decomposition rates (mg g−1 d−1) of mixed-species leaf litter from two experimental designs: 1) a microcosm experiment with litterbags of species mixtures combining six tree species, alone and in 42 combinations, and 2) an in situ litterbag experiment with all possible mixture combinations of four herb species (from one to four species). Interaction strengths and directions were measured as deviations from community-weighted means (CWM) of monoculture decomposition values, following the biomass-ratio hypothesis (BRH). Functional diversity was measured as Laliberté and Legendre's functional dispersion (FDis), using leaf dry matter content (LDMC), leaf nitrogen and carbon contents, and proportions of water soluble compounds, cellulose, hemicellulose and lignin. Correlations between FDis and deviations from BRH varied strongly, depending upon the combination of functional traits, the plant type or the environmental conditions, and the way in which prediction error was expressed (absolute or actual deviation). For tree species, FDis that was based on a combination of water soluble compounds, hemicellulose concentration, and LDMC was negatively correlated with interaction strength but positively with its absolute value. For herbs, interaction strength (absolute or actual) decreased as FDis of the mixtures increased, based on cellulose and lignin contents. There was no positive correlation between functional dispersion and the deviations from Grime's biomass-ratio hypothesis, with a null intercept. Despite a relationship between litter interactions and functional divergence, this relationship was not generalisable. Other functional traits that were missing in our study might have played an important role.
... These results also supported the assumptions we have used to rationalize our second hypothesis, which predicted that due to functional differences in litter quality, the mixture of flower and leaf litter would cause LMEs on the decomposition of both litter types. Studies in both terrestrial and aquatic ecosystems have shown that the litter functional dissimilarity rather than litter species number is the most important factor causing LMEs on decomposition (Epps et al., 2007;Lecerf et al., 2011;Violle et al., 2017). Our study supports this paradigm in demonstrating that LMEs on decomposition can also occur intraspecifically via the interaction of flower and leaf litter and call attention to the importance of LMEs on decomposition even in low-diversity systems through the interactions of litter from different plant organs. ...
The diversity effect on decomposition, through the litter-mixing effects plays a central role in determining the nutrient and carbon dynamics in ecosystems. However, the litter-mixing effects are centered on a leaf litter perspective. Important aspects related to intraspecific interaction and biomass concentration are rarely evaluated, even though they could be essential to determine the litter decomposition dynamics. To our knowledge, we introduced a new perspective to evaluate whether and how the interaction between flower and leaf litter affects the occurrence, direction, and magnitude of litter-mixing effects in terrestrial and aquatic ecosystems. We performed laboratory experiments using flower and leaf litter from the yellow trumpet tree Tabebuia aurea (Silva Manso) Benth. and Hook. f. ex. S. Moore as a model. To obtain realistic results, we manipulated various scenarios of flower : leaf litter biomass proportion and measured 13 functional traits. Litter-mixing effects were consistent in both aquatic and terrestrial environments, with faster decomposition of both litter types in mixtures compared to their monocultures (synergistic effects). Litter-mixing effects were stronger in the terrestrial environment and at higher flower : leaf litter biomass proportions. Our results indicate that synergistic outcomes are mainly associated with complementary effects. Flower litter had a higher concentration of labile C compounds, N, P, and K and lower lignin concentrations, representing a labile litter, while leaf litter had a higher concentration of lignin, Ca, Mg, and Na, representing a refractory litter. Our results demonstrate the importance of litter-mixing effects between flower and leaf litter via complementary effects. These results shed light on the secondary consequences of flower litter on decomposition, suggesting that species with high reproductive investment in flower biomass may play an important role in the nutrient and carbon recycling of diverse plant communities, exerting a pivotal role in biogeochemical dynamics.
... According to Grime's mass-ratio hypothesis, litter CWM traits can drive decomposition, that is, the relative abundances of the particular traits are more important (Garnier et al., 2004). The niche complementarity hypothesis states that functionally unique species are more important for decomposition than other species, and that complementary resources can be assessed by functional dissimilarity in litter mixtures, which is expressed as Rao's quadratic entropy (Botta-Dukat, 2005;Epps et al., 2007). Henceforth, we calculated "CWM" and "Rao" traits as the mass-ratio and niche complementarity mechanism indices, respectively, then, we calculated the litter CWM and Rao values according to the following equation: ...
... Categorical classifications (including our scenarios of rare species loss described above) have several limitations, such as the lack of variation within categorical groups (Ricotta 2005). Therefore, Rao's quadratic entropy index was used to determine the functional diversity of litter mixtures (Epps et al. 2007). This was calculated using the same above-mentioned litter traits (N and P concentrations and toughness) weighted by initial dry mass of each species in the sample, using the dbFD function in FD package (Laliberté and Legendre 2010). ...
... More work is needed to understand the underlying mechanisms behind these species-specific effects of mixtures on N loss. Nevertheless, our results highlight that magnitude and benefits of residue mixing go beyond the simple legume/ grass dichotomy and can be highly species-specific (Epps et al. 2007;Heemsbergen et al. 2004;Lecerf et al. 2011). ...
Background and aimsCover crops are an integral constituent of sustainable subtropical agroecosystems. Using grass/legume mixtures as opposed to monocultures has the potential to maximize their multifunctionality. This project aimed to understand temporal patterns of nitrogen (N) release of cover crop monocultures and mixtures in a subtropical vegetable production system.MethodsA litterbag experiment was established to study N release patterns of two commonly used grasses, two legumes, four two-species mixture each with one grass and one legume, and one four-species mixture. This field experiment was complemented by two laboratory incubations to quantify soil N mineralization after the termination of cover crops in 2020 and 2021.ResultsThe majority of residue N (> 60%) was lost in the first month of decomposition, suggesting no or minimal N release from cover crops beyond one cropping season. Mixtures enhanced N release relative to monocultures within the first two months; however, the timing of this synergistic effect depended on grass species in the mixture. Initial residue N concentration reasonably predicted the N loss trajectory of all residue types (r = -0.72; p < 0.05). Legumes showed the highest N mineralization rate, followed by mixtures and lastly grasses.Conclusions
Our findings reveal significant temporal variability in N release among different cover crop mixtures, despite the rapid decomposition across all cover crop treatments. Selection of appropriate species in cover crop mixtures helps to facilitate the synchronization of N release and crop update in subtropical systems where N management is extremely time sensitive.
... According to Grime's mass-ratio hypothesis, litter CWM traits can drive decomposition, that is, the relative abundances of the particular traits are more important (Garnier et al., 2004). The niche complementarity hypothesis states that functionally unique species are more important for decomposition than other species, and that complementary resources can be assessed by functional dissimilarity in litter mixtures, which is expressed as Rao's quadratic entropy (Botta-Dukat, 2005;Epps et al., 2007). Henceforth, we calculated "CWM" and "Rao" traits as the mass-ratio and niche complementarity mechanism indices, respectively, then, we calculated the litter CWM and Rao values according to the following equation: ...
Plant litter-derived dissolved compounds leaching is an important process for soil carbon (C) sequestration and nutrient cycling. However, knowledge of the biotic and abiotic drivers of dissolved compound release from litter mixture remains limited. Here, we evaluated the loss of soluble C, N, and P during litter mixtures decomposition across an alpine treeline ecotone, and we sought to assess the relative importance of environmental conditions, litter diversity (functional dissimilarity (Rao) and community-weighted mean (CWM) traits), litter chemistry (C quality, nutrients, and stoichiometry) and microbe drive dissolved compound release during the decomposition process. The results showed that dissolved compound release from litter mixtures deviated from predictions based on litter monoculture, with predominantly synergistic effects, and the hierarchical drivers suggested: temperature strongly regulated the release of dissolved compounds and its non-additivity. In particular, freeze-thaw cycles and seasonal snow accelerated the synergistic effects on dissolved compound loss. Litter CWM and Rao traits only accelerated soluble C release and the synergistic effects of soluble P at the last stage of dissolved compound loss, respectively. Litter nutrients directly drove the release of soluble C and P at different stages. Litter C quality and microbes regulated the release of soluble C and P via direct effects, and stoichiometry had an indirect impact, which mainly before 40 % of initial mass loss. Yet, litter chemistry showed a minimal effect on soluble N release, so controls established for the release of soluble C and P might not be valid for soluble N during decomposition. Collectively, our findings advocate the decomposition environment and litter nutrients are key factors for controlling the dissolved compounds leaching, then followed by the interactions of litter C quality, stoichiometry, litter functional diversity, and microbe, which is important for understanding soil organic matter pool and soil fertility in alpine ecosystems.
... The difference in SOC accumulation between birch and pine plots found here may also be explained by differences in quality of leaf litter (Brovkin et al., 2012;Dorrepaal, Cornelissen, Aerts, Wallén, & Van Logtestijn, 2005;Epps, Comerford, Reeves, Cropper, & Araujo, 2007;Parker et al., 2018) and root exudates (Smith, 1976), resulting in slower C turnover in the coniferous pine stands relative to the deciduous birch stands (Melvin et al., 2015; Figure 4). The combined above-and below-ground C stocks in the pine plots were similar to heather control plots 12 years after planting, indicating that planting pine trees onto heather moorlands may lead to little change in ecosystem C sequestration in the short to medium term (~12 years). ...
Tree planting is increasingly being proposed as a strategy to combat climate change through carbon (C) sequestration in tree biomass. However, total ecosystem C storage that includes soil organic C (SOC) must be considered to determine whether planting trees for climate change mitigation results in increased C storage. We show that planting two native tree species (Betula pubescens and Pinus sylvestris), of widespread Eurasian distribution, onto heather (Calluna vulgaris) moorland with podzolic and peaty podzolic soils in Scotland, did not lead to an increase in net ecosystem C stock 12 or 39 years after planting. Plots with trees had greater soil respiration and lower SOC in organic soil horizons than heather control plots. The decline in SOC cancelled out the increment in C stocks in tree biomass on decadal timescales. At all four experimental sites sampled, there was no net gain in ecosystem C stocks 12–39 years after afforestation—indeed we found a net ecosystem C loss in one of four sites with deciduous B. pubescens stands; no net gain in ecosystem C at three sites planted with B. pubescens; and no net gain at additional stands of P. sylvestris. We hypothesize that altered mycorrhizal communities and autotrophic C inputs have led to positive ‘priming’ of soil organic matter, resulting in SOC loss, constraining the benefits of tree planting for ecosystem C sequestration. The results are of direct relevance to current policies, which promote tree planting on the assumption that this will increase net ecosystem C storage and contribute to climate change mitigation. Ecosystem‐level biogeochemistry and C fluxes must be better quantified and understood before we can be assured that large‐scale tree planting in regions with considerable pre‐existing SOC stocks will have the intended policy and climate change mitigation outcomes.
... Some studies have supported a chemical diversity approach toward elucidating the belowground effects of aboveground diversity (Hoorens et al. 2003;Smith and Bradford 2003). Epps et al. (2007) demonstrated that accounting for chemical variation was more informative regarding decomposition than was species diversity. While the usefulness of trait-based dissimilarity approaches remains somewhat equivocal (Frainer et al. 2015), there is increasing support for such trait-based approaches in explaining variation in leaf litter decomposition (Fortunel et al. 2009;Finerty et al. 2016;Jewell et al. 2017;Fujii et al. 2017). ...
Above- and belowground systems are linked via plant chemistry. In forested systems, leaf litter chemistry and quality mirror that of green foliage and have important afterlife effects. In systems where belowground inputs dominate, such as grasslands, or in ecosystems where aboveground biomass is frequently removed by burning or harvesting, foliar traits may provide important information regarding belowground inputs via exudates and fine-root turnover. Many, if not most, of the plant traits that drive variation in belowground processes are also measurable via remote sensing technologies. The ability of remote sensing techniques to measure fine-scale biodiversity and plant chemistry over large spatial scales can help researchers address ecological questions that were previously prohibitively expensive to address. Key to these potential advances is the idea that remotely sensed vegetation spectra and plant chemistry can provide detailed information about the function of belowground processes beyond what traditional field sampling can provide.
... Chemical diversity was assessed both in terms of compound richness (the total number of compounds per sample), and through calculation of a chemical diversity index (H C ) per sample, following previous authors (Epps et al., 2007;Meier and Bowman, 2008). Calculation of this index used the same equation as for Shannon-Wiener diversity (computed using the vegan 'diversity' function). ...
Crop domestication can lead to weakened expression of plant defences, with repercussions for herbivore and pathogen susceptibility. However, little is known about how domestication alters traits that mediate other important ecological interactions in crops, such as pollination. Secondary metabolites, which underpin many defence responses in plants, also occur widely in nectar and pollen and influence plant-pollinator interactions. Thus, domestication may also affect secondary compounds in floral rewards, with potential consequences for pollinators. To test this hypothesis, we chemically analysed nectar and pollen from wild and cultivated plants of highbush blueberry (Vaccinium corymbosum L.), before conducting an artificial diet bioassay to examine pollinator-pathogen interactions. Our results indicated that domestication has significantly altered the chemical composition of V. corymbosum nectar and pollen, and reduced pollen chemical diversity in cultivated plants. Of 20 plant metabolites identified in floral rewards, 13 differed significantly between wild and cultivated plants, with a majority showing positive associations with wild compared to cultivated plants. These included the amino acid phenylalanine (4.5 times higher in wild nectar, 11 times higher in wild pollen), a known bee phagostimulant and essential nutrient; and the antimicrobial caffeic acid ester 4-O-caffeoylshikimic acid (two times higher in wild nectar). We assessed the possible biological relevance of variation in caffeic acid esters in bioassays, using the commercially available 3-O-caffeoylquinic acid. This compound reduced Bombus impatiens infection by a prominent gut pathogen (Crithidia) at concentrations that occurred in wild but not cultivated plants, suggesting that domestication may influence floral traits with consequences for bee health. Appreciable levels of genetic variation and heritability were found for most floral reward chemical traits, indicating good potential for selective breeding. Our study provides the first assessment of plant domestication effects on floral reward chemistry and its potential repercussions for pollinator health. Given the central importance of pollinators for agriculture, we discuss the need to extend such investigations to pollinator-dependent crops more generally and elaborate on future research directions to ascertain wider trends, consequences for pollinators, mechanisms, and breeding solutions.
... In our system, complementarity was the main process underlying diversity-decomposition relationships under ambient conditions, when detritivore abundance followed the palatability of the litter species. Although our experiment does not explore the reasons for this complementarity, in other systems litter mixtures are thought to provide a more balanced diet for detritivores (Epps et al. 2007). This effect has been often attributed to the elemental and structural differences between litter species (Schimel andH€ attenschwiler 2007, Gessner et al. 2010). ...
Climate change and biodiversity loss are expected to simultaneously affect ecosystems, however research on how each driver mediates the effect of the other has been limited in scope. The multiple stressor framework emphasizes non‐additive effects, but biodiversity may also buffer the effects of climate change, and climate change may alter which mechanisms underlie biodiversity–function relationships. Here, we performed an experiment using tank bromeliad ecosystems to test the various ways that rainfall changes and litter diversity may jointly determine ecological processes. Litter diversity and rainfall changes interactively affected multiple functions, but how depends on the process measured. High litter diversity buffered the effects of altered rainfall on detritivore communities, evidence of insurance against impacts of climate change. Altered rainfall affected the mechanisms by which litter diversity influenced decomposition, reducing the importance of complementary attributes of species (complementarity effects), and resulting in an increasing dependence on the maintenance of specific species (dominance effects). Finally, altered rainfall conditions prevented litter diversity from fueling methanogenesis, because such changes in rainfall reduced microbial activity by 58%. Together, these results demonstrate that the effects of climate change and biodiversity loss on ecosystems cannot be understood in isolation and interactions between these stressors can be multifaceted.
... The discrepancies in litter quality present in mixtures may play a more important role where more litter accumulates due to, for example, time-mediated vertical differences in the decomposition stage across thicker litter layers. Chemical dissimilarity (Epps et al., 2007;Hättenschwiler, 2005;Hättenschwiler and Jørgensen, 2010) and its impact on the selective feeding of decomposers Palmer, 2006a, 2006b) has also been demonstrated to play a role in litter mixtures effects. These selective feeding may depend on the proportion of high quality detritus in mixtures, and therefore, strongly depend on the amount of litter biomass in the standing stock. ...
Leaf litter mixtures and the amount of litter biomass in the litter standing stocks can affect the decomposition rates by modifying physical properties and resource heterogeneity in the litter layers. However, the potential interactive effects of litter mixtures and the amount of litter biomass on decomposition have been overlooked in the literature, even though both aspects of litter layer may be highly variable in space and time, within and across ecosystems. In a field experiment conducted in a seasonally dry tropical forest (also known as restinga forest), we investigated the individual and interactive effects of litter mixing and litter biomass on the decomposition of leaf litter from four species of trees, at both species- and assemblage-level. We hypothesized that the mixing of litter and higher litter biomass would both promote litter decomposition, and that litter mixture effects on decomposition at assemblage- and species specific-level would be stronger under higher litter biomass. Mixing of litter and the amount of litter in the standing stocks had no significant individual effects on decomposition, neither at the assemblage- or species specific-level. However, we observed an interactive effect between both experimental factors for the decomposition of a single species, where, contrary to our predictions, the decomposition of Andira legalis at low litter biomass was slightly reduced in the litter mixture. Our results indicate that litter decomposition in the restinga ecosystem should be highly predictable with knowledge of species composition and species-specific decomposition rates, and suggest that, at least for seasonally dry tropical ecosystems, the mixing of litter may have only a small effect on the decomposition process.
... Ball et al., 2008;Lecerf et al., 2011;Barantal et al., 2014;Handa et al., 2014). These effects arise from the variation of species-specific physical and chemical litter traits represented in litter mixtures, as predicted theoretically by Epps et al. (2007), and reported empirically for example by Barantal et al. (2014) and Handa et al. (2014). By contrast, Grime's biomass ratio hypothesis (Grime, 1998) predicts that any litter composition effect is driven by community-weighted mean (CWM) traits (Garnier et al., 2004), that is, the average trait values calculated from the species-specific values and the relative abundance of the species present in the mixture, which a priori excludes nonadditive effects. ...
It is estimated that 4.5 trillion cigarette butts are discarded annually, making them numerically the most common type of litter on Earth. To accelerate their disappearance after disposal, a new type of cigarette filters made of cellulose, a readily biodegradable compound, has been introduced in the market. Yet, the advantage of these cellulose filters over the conventional plastic ones (cellulose acetate) for decomposition, remains unknown. Here, we compared the decomposition of cellulose and plastic cigarettes filters, either intact or smoked, on the soil surface or within a composting bin over a six-month field decomposition experiment. Within the compost, cellulose filters decomposed faster than plastic filters, but this advantage was strongly reduced when filters had been used for smoking. This indicates that the accumulation of tars and other chemicals during filter use can strongly affect its subsequent decomposition. Strikingly, on the soil surface, we observed no difference in mass loss between cellulose and plastic filters throughout the incubation. Using a first order kinetic model for mass loss of for used filters over the short period of our experiment, we estimated that conventional plastic filters take 7.5-14 years to disappear, in the compost and on the soil surface, respectively. In contrast, we estimated that cellulose filters take 2.3-13 years to disappear, in the compost and on the soil surface, respectively. Our data clearly showed that disposal environments and the use of cellulose filters must be considered when assessing their advantage over plastic filters. In light of our results, we advocate that the shift to cellulose filters should not exempt users from disposing their waste in appropriate collection systems.
... It is well established that the chemical nature of leaf litter affects the rates of decomposition in terrestrial ecosystems [26,27]. Generally, at the ecosystem level, litter quality is most often related to the chemical characteristics of the litter such as carbon content, nitrogen content, C-to-N ratio, lignin, condensed tannins, hydrolyzable tannins, phenols, and carbohydrates (e.g., cellulose and hemicellulose) [3,12,28] (Table 2). ...
Litter decomposition is controlled by chemical traits such as lignin, tannins, phenols, carbohydrates, nitrogen content, and C-to-N ratio. These chemicals may change the soil biogeochemistry and enter the soil from litter. This paper (1) provides a broad overview of litter chemistry and decomposition (2) as well as their effects on biogeochemistry of soil in forest ecosystems. Most studies focus on litter chemical effects on decomposition. Here we discussed litter chemistry and its relation to decomposition. This study discusses how litter chemistry has significant effects on soil biogeochemistry and looks into the relationships between litter chemistry, soil chemistry and microbial activity. Further investigations into the relationship among the litter creating substrate - microbe - soil chemistry are needed. In particular identification of mechanisms of interactions between tannins, tannin-like phenolics, and soil organic matter is needed. The fate of lignin and phenolics after they enter the soil, is of ecological and environmental importance but remains incompletely understood.
... Ball et al., 2008;Lecerf et al., 2011;Barantal et al., 2014;Handa et al., 2014). These effects arise from the variation of species-specific physical and chemical litter traits represented in litter mixtures, as predicted theoretically by Epps et al. (2007), and reported empirically for example by Barantal et al. (2014) and Handa et al. (2014). By contrast, Grime's biomass ratio hypothesis (Grime, 1998) predicts that any litter composition effect is driven by community-weighted mean (CWM) traits (Garnier et al., 2004), that is, the average trait values calculated from the species-specific values and the relative abundance of the species present in the mixture, which a priori excludes nonadditive effects. ...
Different tree species influence litter decomposition directly through species‐specific litter traits, and indirectly through distinct modifications of the local decomposition environment. Whether these indirect effects on decomposition are influenced by tree species diversity is presently not clear.
We addressed this question by studying the decomposition of two common substrates, cellulose paper and wood sticks, in a total of 209 forest stands of varying tree species diversity across six major forest types at the scale of Europe.
Tree species richness showed a weak but positive correlation with the decomposition of cellulose but not with that of wood. Surprisingly, macroclimate had only a minor effect on cellulose decomposition and no effect on wood decomposition despite the wide range in climatic conditions among sites from Mediterranean to boreal forests. Instead, forest canopy density and stand‐specific litter traits affected the decomposition of both substrates, with a particularly clear negative effect of the proportion of evergreen tree litter.
Our study suggests that species richness and composition of tree canopies modify decomposition indirectly through changes in microenvironmental conditions. These canopy‐induced differences in the local decomposition environment control decomposition to a greater extent than continental‐scale differences in macroclimatic conditions.
... Since this correlation was weak (marginal R 2 0.07), in the opposite direction of that provided in our a priori hypothesis, and since we can expect to find one significant correlation by chance for every 20 traits tested, we treat this result with caution. However, although fast plant relative growth rate is often associated with high litter quality and therefore rapid decomposition (Garnier and Navas 2012), a negative correlation between EV-10 on the identity of the species included in the litter mixture (Epps et al. 2007). It is then perhaps not surprising that litter chemical diversity (with its direct link to synergistic mechanisms) and not taxonomic richness would increase decomposition rates. ...
The decomposition of plant material is an important ecosystem process influencing both carbon cycling and soil nutrient availability. Quantifying how plant diversity affects decomposition is thus crucial for predicting the effect of the global decline in plant diversity on ecosystem functioning. Plant diversity could affect the decomposition process both directly through the diversity of the litter, and/or indirectly through the diversity of the host plant community and its affect on the decomposition environment. Using a biodiversity experiment with trees in which both functional and taxonomic diversity were explicitly manipulated independently, we tested the effects of the functional diversity and identity of the living trees separately and in combination with the functional diversity and identity of the decomposing litter on rates of litter decomposition and soil respiration. Plant traits, predominantly leaf chemical and physical traits, were correlated with both litter decomposition and soil respiration rates. Surface litter decomposition, quantified by mass loss in litterbags, was best explained by abundance-weighted mean trait values of tree species from which the litter was assembled (functional identity). In contrast, soil respiration, which includes decomposition of dissolved organic carbon and root respiration, was best explained by the variance in trait values of the host trees (functional diversity). This research provides insight into the effect of loss of tree diversity in forests on soil processes. Such understanding is essential to predicting changes in the global carbon budget brought on by biodiversity loss.
... Since this correlation was weak (marginal R 2 0.07), in the opposite direction of that provided in our a priori hypothesis, and since we can expect to find one significant correlation by chance for every 20 traits tested, we treat this result with caution. However, although fast plant relative growth rate is often associated with high litter quality and therefore rapid decomposition (Garnier and Navas 2012), a negative correlation between EV-10 on the identity of the species included in the litter mixture (Epps et al. 2007). It is then perhaps not surprising that litter chemical diversity (with its direct link to synergistic mechanisms) and not taxonomic richness would increase decomposition rates. ...
Description
No.Sp – number of species CO2 – rates of soil respiration in µmolCO2m-2s-1 K – decomposition rate of home litter in d-1 ComsubK – decomposition rate of common substrate (“Common litter experiment”) Pred.CO2 – soil respiration rates predicted from those in monospecific plots Pred.K – decomposition rates of home litter predicated from those in monospecific plots Pred.ComsubK – decomposition rates of the common substrate predicted from the same common substrate decomposition in monoculture plots Dev.pred – (observed – predicted) CWM – community-weighted mean FD- functional Diversity Traits maxH – max height GR – growth rate LS – leaf size WD – wood density WDR – wood decay resistence Sem – seed mass RoH – root habut AM - Arbuscular mycorrhizas (Endomycorrhiza ) EM - Ectomycorrhizas Rdiam – root diameter Llo – lead longevity Lma – leaf mass per area Nleaf – leaf nitrogen content C – litter carbon content N – litter carbon content LDMC – leaf dry matter content SLA – specific leaf area
... Since this correlation was weak (marginal R 2 0.07), in the opposite direction of that provided in our a priori hypothesis, and since we can expect to find one significant correlation by chance for every 20 traits tested, we treat this result with caution. However, although fast plant relative growth rate is often associated with high litter quality and therefore rapid decomposition (Garnier and Navas 2012), a negative correlation between EV-10 on the identity of the species included in the litter mixture (Epps et al. 2007). It is then perhaps not surprising that litter chemical diversity (with its direct link to synergistic mechanisms) and not taxonomic richness would increase decomposition rates. ...
The decomposition of plant material is an important ecosystem process influencing both carbon cycling and soil nutrient availability. Quantifying how plant diversity affects decomposition is thus crucial for predicting the effect of the global decline in plant diversity on ecosystem functioning. Plant diversity could affect the decomposition process both directly through the diversity of the litter, and/or indirectly through the diversity of the host plant community and its affect on the decomposition environment. Using a biodiversity experiment with trees in which both functional and taxonomic diversity were explicitly manipulated independently, we tested the effects of the functional diversity and identity of the living trees separately and in combination with the functional diversity and identity of the decomposing litter on rates of litter decomposition and soil respiration. Plant traits, predominantly leaf chemical and physical traits, were correlated with both litter decomposition and soil respiration rates. Surface litter decomposition, quantified by mass loss in litterbags, was best explained by abundance-weighted mean trait values of tree species from which the litter was assembled (functional identity). In contrast, soil respiration, which includes decomposition of dissolved organic carbon and root respiration, was best explained by the variance in trait values of the host trees (functional diversity). This research provides insight into the effect of loss of tree diversity in forests on soil processes. Such understanding is essential to predicting changes in the global carbon budget brought on by biodiversity loss. This article is protected by copyright. All rights reserved.
... At the plant community level, studies have shown that aggregated traits, i.e., traits that are weighted by the abundance of each species, can be closely correlated with the decomposition rate of the litter mixtures (Garnier et al. 2004;Quested et al. 2007;Quétier, Thebault & Lavorel 2007;Fortunel et al. 2009). Rather than aggregated traits values, the dissimilarity of litter traits within plant communities can also be used to explain how the plant community composition influences the decomposition of mixed litter (Epps et al. 2007;Barantal et al. 2011). However, these approaches do not account for the widely observed synergistic or antagonistic interactions between the decomposing litter of different plant species through litter mixing effects (Gartner & Cardon 2004;Santonja et al. 2015;Chomel et al. 2016). ...
A broad and diversified group of compounds, secondary metabolites, are known to govern species interactions in ecosystems. Recent studies have shown that secondary metabolites can also play a major role in ecosystem processes, such as plant succession or in the process of litter decomposition, by governing the interplay between plant matter and soil organisms.
We reviewed the ecological role of the three main classes of secondary metabolites and the methodological challenges and novel avenues for their study. We highlight emerging general patterns of the impacts of secondary metabolites on decomposer communities and litter decomposition and argue for the consideration of secondary compounds as key drivers of soil functioning and ecosystem functioning.
Synthesis . Gaining a greater understanding of plant–soil organisms relationships and underlying mechanisms, including the role of secondary metabolites, could improve our ability to understand ecosystem processes. We outline some promising directions for future research that would stimulate studies aiming to understand the interactions of secondary metabolites across a range of spatio‐temporal scales. Detailed mechanistic knowledge could help us to develop models for the process of litter decomposition and nutrient cycling in ecosystems and help us to predict future impacts of global changes on ecosystem functioning.
... Plant species traits are predominant control on litter decomposition rates, and litter quality (i.e., N:C ratios) alters decomposers' respiration rates and the decomposition of single-species litters ( Cornwell et al. 2008;Manzoni et al. 2008). However, the composition and diversity of chemical compounds in litter are potentially important functional traits and affect decomposition ( Epps et al. 2007). For example, condensed tannins in plants consistently slow rates of litter decomposition ( Schweitzer et al. 2008). ...
Forest Ecosystems exchange energy, water, and nutrients and, in particular, carbon (C) with surrounding ecosystems, and play a major role in the global C cycle. Forests are major terrestrial C sinks, have large C densities and sequester large amounts of atmospheric carbon dioxide (CO2). By various natural processes, C is entering forest ecosystems in dissolved, gaseous and particulate form. The C is temporarily stored, and sequestered in above- and belowground pools in vegetation, detritus and soil. Efflux processes result in C losses to adjacent ecosystems. This chapter describes C in- and efflux processes, the C turnover within forest ecosystems and how C is sequestered in the different forest ecosystem pools with a focus on processes occurring in trees and soil.
... Species richness is often used but does not account specifically for functional differences among species, making mechanismdriven predictions of biodiversity-functioning relationships difficult. An increasing number of species does not necessar-ily reflect a parallel increase in functional differences among species (Epps et al. 2007, Cadotte et al. 2011) and can even decrease ecosystem process rates due to antagonistic interactions (e.g. competition), as shown experimentally with bacterial communities (Jousset et al. 2011). ...
... Species richness is often used but does not account specifically for functional differences among species, making mechanismdriven predictions of biodiversity-functioning relationships difficult. An increasing number of species does not necessar-ily reflect a parallel increase in functional differences among species (Epps et al. 2007, Cadotte et al. 2011) and can even decrease ecosystem process rates due to antagonistic interactions (e.g. competition), as shown experimentally with bacterial communities (Jousset et al. 2011). ...
The role of biodiversity for soil processes remains poorly understood. Existing evidence suggests that functional diversity rather than species richness is relevant for soil functioning. However, the importance of functional diversity has rarely been assessed simultaneously at more than one trophic level, critically limiting the prediction of consequences of biodiversity loss for soil functioning. In a laboratory microcosm experiment, we tested the hypothesis that increasing functional dissimilarity of both litter-feeding soil fauna and litter mixtures interactively affects the rates of five different soil processes related to litter decomposition. We created trait-based functional dissimilarity gradients using five assemblages of two detritivore species and five mixtures of two plant litter species commonly found in Mediterranean shrubland ecosystems of southern France. With increasing drought periods predicted for Mediterranean ecosystems in the future, we additionally included two different watering frequencies to evaluate the impact of drought on soil processes and how drought interacts with functional dissimilarity. The different fauna assemblages and litter mixtures showed strong effects on litter mass loss, soil organic carbon and nitrogen leaching, as well as on soil microbial activities. Up to 20% of the variation in response variables was explained by functional dissimilarity, suggesting an ecologically relevant impact of functional diversity on soil process rates. Detritivore functional dissimilarity tended to have stronger effects when combined with increasingly dissimilar litter mixtures, suggesting that trait dissimilarity interacts across trophic levels. Drought affected several soil processes but did not modify the relationships between functional dissimilarity and process rates. Our results indicate that trait diversity of detritivore assemblages and litter mixtures is an important predictor of soil process rates. The common and easily measurable traits used in our study suggest straightforward application across different types of ecosystems and environmental conditions.
... Changes in species diversity or the quality of a species in a mix might have a disproportionate impact on root decomposition and subsequent soil organic matter accrual because roots are in direct contact with the soil matrix and thus the decomposer community. In general, plant species diversity has been a poor predictor of leaf litter decomposition rates ( Bardgett and Shine, 1999;Hattenschwiler et al., 2005;Meier and Bowman, 2008;Spehn et al., 2005;Wardle et al., 1997), but the chemical diversity among tissue types is a good predictor of C-mineralization rates ( Epps et al., 2007;Hoorens et al., 2002;Meier and Bowman, 2008;Orwin et al., 2006). In our study, mixing the roots of three species produced under ambient CO 2 significantly enhanced C-mineralization rates relative to the predicted decomposition rate for each species. ...
Background/Question/Methods
Up to 40% of photosynthetically fixed carbon (C) enters the soil via plant roots as labile root exudates. Root exudates control the microbial community structure and its activity and as a result, could regulate the turnover of more recalcitrant plant detritus. Yet, the extent by which root exudates mediate the microbial community structure, its activity and ultimately decomposition rates of more recalcitrant plant material is uncertain. With this study we aimed to 1) determine whether turnover of plant material is regulated by root exudation rates, and 2) identify how changes in root exudation rates impact the soil microbial community structure. In a 14-day laboratory incubation study, we added a synthetic exudate cocktail at 5 different rates of C release (0, 0.72, 1.4, 3.6, 7.2 and 14.4 mg C g-1 dry soil) to soils amended with 13C labeled plant material. We also included soils that received the exudates, but no plant material.
Results/Conclusions Each increase in exudate application rates to soil significantly enhanced total microbial C respiration (i.e. C derived from soil + exudates + roots). After partitioning between soil- and plant-derived C respiration, we found that addition of the low amounts of exudates (i.e. 0.72 mg, 1.4 mg, 3.6 mg C g-1 soil) significantly stimulated decomposition of plant residue by 29%, 13% and 10% respectively, whereas adding exudates at rates exceeding 7.2 mg C g-1 significantly reduced decomposition rates of the plant material by 30% to 50%. These changes were accompanied by a shift in the microbial community structure as determined by Q-PCR. Exudate concentrations in excess of 3.6 mg C g-1 significantly promoted r-strategist fungal and bacterial groups, leading to preferential substrate utilization and a negative priming effect. In contrast, exudate additions at concentrations smaller than 3.6 mg C g-1 soil day-1 did not significantly enhance bacterial or fungal biomass, but triggered metabolic activity of the microbial community resulting in a positive priming effect. These results highlight the importance of root exudation for controlling decomposition rates of plant detritus and determining the structure of microbial communities. Efforts to quantify how labile root derived C inputs affect overall decomposition rates for better estimates of soil C cycling are warranted.
... Systematic shifts in plant traits also affect ecosystem functions, including water uptake, litter decomposition, and biomass production (Cornelissen and Thompson 1997, Diaz et al. 2004, Cornwell et al. 2008, Suding et al. 2008. Processes at the ecosystem scale reflect a complex set of interactions among the species present, their relative abundances, and their trait values (Garnier et al. 2004, Epps et al. 2007. Declines in species diversity within communities can, but need not, reduce the range of traits present there. ...
Background/Question/Methods
Human-induced changes in habitat quantity, disturbance regimes, and propagule pressure have markedly altered Wisconsin upland forest community diversity and structure. Changes we see at the community level are the combined result of individual species responding due to their traits. We investigated how whole-understory traits and metrics of functional diversity have changed over fifty years across Wisconsin. Mesification and plant invasion is likely to shift community-averaged traits towards values typified by weedy, shade-tolerant species. To test this hypothesis, we assembled a database of 30 traits for 230+ Wisconsin understory plant species. Categorical traits were evaluated from the literature or field. For quantitative traits, a minimum of ten individuals across three locations were sampled and averaged. We calculated abundance-weighted trait values for each site.
Results/Conclusions
We found significant variation in measured traits both within and across species. Quantitative traits were significantly different between northern and southern Wisconsin and between time periods. In particular, specific leaf area (SLA) was larger in southern Wisconsin in both time periods, consistent with more graminoids, ferns, and evergreen-leaved species in the north. SLA increased significantly over time in southern Wisconsin, but not in the north. This supports previous work showing increases in shade-tolerant species in the south. In contrast to SLA, other traits including height moved in similar directions in both areas of the state. Our results confirm that landscape-level changes are having significant impacts on the characteristics of plants in Wisconsin forests. Changes in functional attributes at the community scale will have important consequences for ecosystem functioning.
... Systematic shifts in plant traits also affect ecosystem functions, including water uptake, litter decomposition, and biomass production (Cornelissen and Thompson 1997, Diaz et al. 2004, Cornwell et al. 2008, Suding et al. 2008. Processes at the ecosystem scale reflect a complex set of interactions among the species present, their relative abundances, and their trait values (Garnier et al. 2004, Epps et al. 2007. Declines in species diversity within communities can, but need not, reduce the range of traits present there. ...
Temperate North American forest communities have changed considerably in response to logging, fragmentation, herbivory, and other global change factors. Significant changes in the structure and composition of seemingly undisturbed Wisconsin forest communities have occurred over the past 50 years, including widespread declines in alpha and beta species diversity. To investigate how shifts in species composition have affected distributions of plant functional traits, we first compiled extensive data on understory plant species traits. We then computed community-weighted trait means and functional diversity metrics for communities in both the 1950s and 2000s. We examined how trait values and diversity varied across environmental gradients and among Wisconsin's four main ecoregions. Trait means and diversity values reflect conspicuous gradients in species composition, soils, and climatic conditions. Over the past 50 years, values of most traits have changed as communities shifted toward species with higher leaf nutrient levels and specific leaf area, particularly in the southern ecoregions. Trait richness and diversity have declined, particularly in historically species- and trait-rich unglaciated southwestern Wisconsin. Reductions in within-site trait diversity may be diminishing the ability of these forest communities to resist or resiliently respond to shifts in environmental conditions. Despite changes in trait and community composition, trait–environment relationships measured directly via fourth-corner analysis remain strong for most plant traits. Nevertheless, accelerating ecological change (including climate change) could outstrip the ability of plant species and traits to match their environment, particularly in more fragmented landscapes.
... Non-additive litter decomposition in mixtures may be either synergistic or antagonistic resulting in faster or slower decomposition of litter in mixtures as compared to the additive model. It has been suggested that primarily chemical and physical interactions between litter species contribute to non-additive effects (Hoorens et al. 2003, Epps et al. 2007, Liu et al. 2007. For example, according to Hättenschwiler et al. (2005) the transfer of inhibitory litter constitutes and nutrients can either decelerate or accelerate the decomposition of cooccurring litter species within litter mixtures. ...
Synergistic effects on decomposition in litter mixtures have been suggested to be due to the transfer of nitrogen from N-rich to N-poor species. However, the dominant pathway and the underlying mechanisms remain to be elucidated. We conducted an experiment to investigate and quantify the control mechanisms for nitrogen transfer between two litter species of contrasting nitrogen status (¹⁵N labeled and unlabeled Fagus sylvatica and Fraxinus excehior) in presence and absence of micro-arthropods. We found that ¹⁵N was predominantly transferred actively aboveground by saprotrophic fungi, rather than belowground or passively by leaching. However, litter decomposition remained unaffected by N-dynamics and was poorly affected by micro-arthropods, suggesting that synergistic effects in litter mixtures depend on complex environmental interrelationships. Remarkably, more ¹⁵N was transferred from N-poor beech than N-rich ash litter. Moreover, the low transfer of ¹⁵N from ash litter was insensitive to destination species whereas the transfer of ¹⁵N from labeled beech litter to unlabeled beech was significantly greater than the amount of 15 N transferred to unlabeled ash suggesting that processes of nitrogen transfer fundamentally differ between litter species of different nitrogen status. Microbial analyses suggest that nitrogen of N-rich litter is entirely controlled by bacteria that hamper nitrogen capture of microbes in the environment supporting the source-theory. In contrast, nitrogen of N-poor fungal dominated litter is less protected and transferable depending on the nitrogen status and the transfer capacity of the microbial community of the co-occurring litter species supporting the gradient-theory. Thus, our results challenge the traditional view regarding the role of N-rich litter in decomposing litter mixtures. We rather suggest that N-rich litter is only a poor nitrogen source, whereas N-poor litter, can act as an important nitrogen source in litter mixtures. Consequently both absolute and relative differences in initial litter C/N ratios of co-occurring litter species need to be considered for understanding nitrogen dynamics in decomposing litter mixtures.
... Studies have long recognized the non-additive effects of plant species diversity on litter decomposition, but have failed to generalize the magnitude and direction of such effects (Gartner & Cardon 2004;H€ attenschwiler, Tiunov & Scheu 2005;Vos et al. 2011). Recently, chemical and physical leaf litter traits were proposed as better parameters explaining the effects of litter mixtures on decomposition (Epps et al. 2007;Meier & Bowman 2008;Barantal et al. 2011). When CWM and FD of these leaf litter traits were considered, the results of these works suggested that CWM plays a major role compared with FD on driving litter decomposition (Grigulis et al. 2013). ...
There is a growing consensus that the distribution of species trait values in a community can greatly determine ecosystem processes and services delivery. Two distinct components of community trait composition are hypothesized to chiefly affect ecosystem processes: (i) the average trait value of the species, quantified by community‐weighted mean trait values ( CWM ; related to the mass ratio hypothesis) and (ii) the degree to which trait values differ between species in a community, quantified by different indices of functional diversity ( FD ; related to non‐additive community effects). The uncertainty on the relative effect of these two components is stimulating an increasing number of empirical studies testing their effects on ecosystem processes and services delivery.
We suggest, however, that the interdependence between CWM and FD poses a challenge on disentangling their relative importance. We present a framework that allows designing experiments to decouple and assess the effects of these two community functional components on ecosystem processes and services. To illustrate the framework, we focused on leaf litter decomposition, as this is an essential process related to important ecosystem services. Using simulations, we applied the framework for plant leaf litter traits (litter nitrogen and phenolic content) that are related to litter decomposition.
CWM and FD generally showed a hump‐shaped relationship (i.e. at more extreme CWM values, communities can have only low FD values). Within this relationship, we showed that it is possible to select quasi‐orthogonal combinations of CWM and FD that can be treated statistically. Within these orthogonal CWM and FD combinations, it is also possible to select species assemblages controlling for other community parameters, such as total biomass, total density and species richness.
Synthesis . The framework provides a novel approach for designing experiments to decouple the effects of CWM and FD of communities on ecosystem processes, which otherwise cannot be easily disentangled. To apply the framework and design proper experimental layouts, it is essential to have a priori knowledge of the key traits by which species affect ecosystem processes and service delivery.
... Many studies show that the number of litter species is much less important in controlling litter mass loss than the taxonomic composition of litter mixture (Wardle et al., 1997;Kominoski et al., 2007;Schindler and Gessner, 2009;Swan et al., 2009). The functional trait approach represents a promising framework to explain patterns of non-additive litter mixing effects across species mixtures (Epps et al., 2007;Meier and Bowman, 2008;Hoorens et al., 2010). It is expected that non-additive litter mixing effects will be stronger in litter mixtures consisting of species with dissimilar physical and chemical traits than in litter mixtures made of functionally equivalent species (Schindler and Gessner, 2009 , temperature sensitivity of mixed litter mass loss (Q 10 ) (B) and non-additive effects (C and D) and S: shrub; F: forbs; G: graminoids. ...
Few studies of the effects of litter diversity on the temperature sensitivity of mixed litter mass loss (MLML) are available. We tested the hypothesis that high litter diversity would reduce the magnitude of effects of climate and environmental change on MLML with 0.5/1 mm litter bags and sampling once after 1 yr of decomposition, using 51 combinations of litter mixtures from 25 dominant species at 3200 and 3800 m elevations on the Tibetan Plateau. Generally, our study supported our hypothesis. High temperature (i.e. lower elevation) reduced the dependency of MLML and non-additive effects on species richness. Species composition significantly affected MLML and its Q10 (i.e. the ratio of litter mass loss rate at a temperature T1 that is 10 °C lower than a temperature T2) when species richness was less than 8. Shrubs significantly decreased the Q10 of MLML when the species richness of litter mixture was less than 4. These findings suggest that the influence of future warming on MLML may depend on the balance between the magnitude of the impacts of climate change on shrub invasion and loss of species diversity in alpine region.
... The functional trait approach represents a promising framework to explain patterns of nonadditive littermixing effects across species mixtures (Epps et al. 2007, Meier and Bowman 2008). Following recent findings on effects of litter chemical diversity on soil carbon and nitrogen dynamics (Meier and Bowman 2008) and current mechanistic understanding of litter mixture decomposition (Ha¨ttenschwiler et al. 2005), it is expected that nonadditive litter-mixing effects will be stronger in litter mixtures consisting of species with dissimilar physical and chemical traits than in litter mixtures made of functionally equivalent species (Schindler and Gessner 2009). ...
Plant diversity influences many fundamental ecosystem functions, including carbon and nutrient dynamics, during litter breakdown. Mixing different litter species causes litter mixtures to lose mass at different rates than expected from component species incubated in isolation. Such nonadditive litter-mixing effects on breakdown processes often occur idiosyncratically because their direction and magnitude change with incubation time, litter species composition, and ecosystem characteristics. Taking advantage of results from 18 litter mixture experiments in streams, we examined whether the direction and magnitude of nonadditive mixing effects are randomly determined. Across 171 tested litter mixtures and 510 incubation time-by-mixture combinations, nonadditive effects on breakdown were common and on average resulted in slightly faster decomposition than expected. In addition, we found that the magnitude of nonadditive effects and the relative balance of positive and negative responses in mixtures change predictably over time, and both were related to an index of functional litter diversity and selected environmental characteristics. Based on these, it should be expected that nonadditive effects are stronger for litter mixtures made of functionally dissimilar species especially in smaller streams. Our findings demonstrate that effects of litter diversity on plant mixture breakdown are more predictable than generally thought. We further argue that the consequences of current worldwide homogenization in the composition of plant traits on carbon and nutrient dynamics could be better inferred from long-duration experiments that manipulate both functional litter diversity and ecosystem characteristics in "hotspots of biodiversity effects,'' such as small streams.
Litter decomposition is the main driver of nutrient cycling process in terrestrial ecosystems. Afforestation completely altered vegetation composition and litter species, disrupting the long-term carbon balance in grassland ecosystem. However, there is a lack of understanding of how litter mixing effect (LME) affects soil carbon cycling in afforested ecosystem. Here, we investigated the effects of litter richness and quality of tree, shrub, and grass species and their litter mixture on soil CO2 fluxes. The results showed that cumulative soil CO2 flux in the early stage (1–28 days) was 1.75 times higher than that in the late stage (29–113 days), indicating litter decomposition was intensive at first and then decreased with time. Soil carbon flux changed with decomposition stages. In the early-stage of decomposition, soil CO2 flux increased with the concentrations of litter carbon, nitrogen and condense tannin. In the late phase of decomposition, all litter chemical traits were negatively related to the soil carbon flux. Additionally, plant litter richness was negatively correlated to early-stage soil CO2 flux, whereas it was positively related to late-stage soil carbon flux. Our results provide evidence that long-term carbon balance in grassland ecosystems was interrupted by afforestation, and the dominant litter chemical traits that controlling soil carbon cycling changed over time.
Biodiversity loss is altering key ecosystem processes as primary production and decomposition, however, the after-life effects of plant diversity (species-mixing effects) on instream organic matter (litter) decomposition is still under debate. Available evidence of litter species-mixing effect (or the lack of) comes from studies using dominant plant species, despite rare species comprising the majority of species in an ecosystem and can contribute to ecosystem functions or in the provisioning of essential elements. Here, we simulated different extinction scenarios of plant from rare species by incubating leaf litter in artificial channels located within a tropical stream. We thus, assessed whether the loss of litter from rare plant species alters functional diversity (resource dissimilarity) and litter quality (resource concentration) of species mixtures and change decomposition, N loss and fungal biomass production. We show that the loss of litter from rare plant species reduced the functional diversity of litter mixtures and consequently, reduced decomposition, N loss and fungal biomass production. Although species lost also changed the nutritional quality of litter mixtures (resource concentration), it did not affect decomposition or N loss but fungal biomass production. Also, when only similar rare species were present, processes were reduced to higher rates than in the scenario with only dissimilar rare species (except for N loss). Our findings reveal the relevance of litter from rare plant species to key ecosystem processes related to carbon and nutrient flow in tropical streams, especially when dissimilar traits are added to litter pools.
Plant litter decomposition is an essential ecosystem function in temperate streams. Both riparian vegetation and decomposer communities are major determinants of the decomposition efficiency and the interactions occurring within litter mixtures. However, the extent to which such litter mixture interactions are affected by combined shifts in litter traits and decomposer community is not well understood. We used leaf litter from 10 European tree species in order to study litter decomposition and litter mixture effects occurring in two-species litter mixtures in a temperate forested stream of northwestern France. The study distinguished between (1) decomposition involving microorganisms alone or together with invertebrates, and (2) decomposition involving litter mixtures of similar or dissimilar nutrient content. Increasing mean litter nutrient concentration favored both microbial activity and litter decomposition rate. Surprisingly, the highest litter mixture effects occurred in mixtures containing two nutrient-rich litters and occurred mainly in macroinvertebrate presence. Both the “mass ratio hypothesis,” expressed as the community-weighted mean traits (TraitCWM), and the “niche complementarity hypothesis,” expressed as the functional dissimilarity of litter traits (TraitFD), contributed to explain litter mixture effects. However, TraitCWM was found to be a better predictor than TraitFD. Finally, when evaluating the individual contributions of litter nutrients, calcium and magnesium appeared as important drivers of litter mixture effects. Our findings suggest that the mass ratio hypothesis overrules the niche complementarity hypothesis as a driver of litter diversity effects. Our study highlights the key importance of macroinvertebrates and of leaf nutrients, such as Ca and Mg, which are often neglected in decomposition studies in streams.
Climate and plant diversity are major determinants of carbon (C) and nitrogen (N) dynamics in decomposing plant litter. However, the direction and extent to which these dynamics are affected by combined changes in climate and biodiversity are not well understood. We used a field experiment in a Mediterranean shrubland ranging from one to four shrub species with partial rain exclusion (− 12%) to test how lower precipitation interacts with shrub species diversity to influence C and N release during decomposition. We also distinguished between first-year (0–12 months) and second-year decomposition (12–24 months) to test the hypothesis of stronger diversity effects at the beginning of the decomposition process. Litter C and N release increased with litter species richness during the first year, but not during the second year of decomposition. However, these richness effects were weak and less consistent than litter composition effects, which persisted over time and became even stronger for C release after 2 years of decomposition. Partial rain exclusion reduced N release by 17% only during the first year and had no effect on C release in either year. Community-weighted mean (CWM) traits and functional dissimilarity (FD) of litter traits contributed both to explain litter species composition effects. These litter trait effects were not altered by partial rain exclusion, but were more important after 2 years than after 1 year of decomposition. Our findings suggest increasing trait legacy effects with ongoing decomposition. More generally, our data showed that changes in the diversity of dominant shrub species had stronger effects on C and N release during litter decomposition than a moderate reduction in precipitation.
Litter decomposition is controlled by chemical traits such as lignin, tannins, phenols, carbohydrates, nitrogen content, and C-to-N ratio. These chemicals may change the soil biogeochemistry and enter the soil from litter. This paper (1) provides a broad overview of litter chemistry and decomposition (2) as well as their effects on biogeochemistry of soil in forest ecosystems. Most studies focus on litter chemical effects on decomposition. Here we discussed litter chemistry and its relation to decomposition. This study discusses how litter chemistry has significant effects on soil biogeochemistry and looks into the relationships between litter chemistry, soil chemistry and microbial activity. Further investigations into the relationship among the litter creating substrate - microbe - soil chemistry are needed. In particular identification of mechanisms of interactions between tannins, tannin-like phenolics, and soil organic matter is needed. The fate of lignin and phenolics after they enter the soil, is of ecological and environmental importance but remains incompletely understood.
Meta-analysis of the first generation of biodiversity experiments has revealed that there is a general positive relationship between diversity and ecosystem processes that is consistent across trophic groups and ecosystem types. However, the mechanisms generating these general patterns are still under debate. While there are unresolved conceptual issues about the nature of diversity and complementarity, the debate is partly due to the difficulty of performing a full-factorial analysis of the functional effects of all species in a diverse community. However, there are now several different analytical approaches that can address mechanisms even when full factorial analysis is not possible. This chapter presents an overview and users' guide to these methods. This chapter concludes that the current toolbox of methods allows investigation of the mechanisms for most, if not all, biodiversity and ecosystem functioning experiments conducted to date that manipulate species within a single trophic level (e.g. plant biodiversity experiments). Methods that can address mechanisms in multitrophic studies are a key need for future research.
Plant leaf litter generally decomposes faster as a group of different species than when individual species decompose alone, but underlying mechanisms of these diversity effects remain poorly understood. Because resource C : N : P stoichiometry (i.e. the ratios of these key elements) exhibits strong control on consumers, we supposed that stoichiometric dissimilarity of litter mixtures (i.e. the divergence in C : N : P ratios among species) improves resource complementarity to decomposers leading to faster mixture decomposition. We tested this hypothesis with: (i) a wide range of leaf litter mixtures of neotropical tree species varying in C : N : P dissimilarity, and (ii) a nutrient addition experiment (C, N and P) to create stoichiometric similarity. Litter mixtures decomposed in the field using two different types of litterbags allowing or preventing access to soil fauna. Litter mixture mass loss was higher than expected from species decomposing singly, especially in presence of soil fauna. With fauna, synergistic litter mixture effects increased with increasing stoichiometric dissimilarity of litter mixtures and this positive relationship disappeared with fertilizer addition. Our results indicate that litter stoichiometric dissimilarity drives mixture effects via the nutritional requirements of soil fauna. Incorporating ecological stoichiometry in biodiversity research allows refinement of the underlying mechanisms of how changing biodiversity affects ecosystem functioning.
* A graduate level text which incorporates the latest developments in the field of biodiversity and ecosystem functioning, one of the most controversial and high profile areas of ecological research
* The first volume to explore the economics of biodiversity and ecosystem services
* Summarizes the eagerly anticipated findings of two large and highly respected scientific networks, BioMERGE and DIVERSITAS
* Builds on the success and influence of the highly cited Biodiversity and Ecosystem Functioning (OUP, 2002)
* The first volume advancing the scientific foundation of the United Nation's global environmental assessment, Millennium Ecosystem Assessment, that links human well-being with the conservation of biodiversity
Carbon Sequestration in Forest Ecosystems is a comprehensive book describing the basic processes of carbon dynamics in forest ecosystems, their contribution to carbon sequestration and implications for mitigating abrupt climate change. This book provides the information on processes, factors and causes influencing carbon sequestration in forest ecosystems. Drawing upon most up-to-date references, this book summarizes the current understanding of carbon sequestration processes in forest ecosystems while identifying knowledge gaps for future research, Thus, this book is a valuable knowledge source for students, scientists, forest managers and policy makers.
Functional diversity is an important component of biodiversity, yet in comparison to taxonomic diversity, methods of quantifying functional diversity are less well developed. Here, we propose a means for quantifying functional diversity that may be particularly useful for determining how functional diversity is related to ecosystem functioning. This measure of functional diversity ''FD'' is defined as the total branch length of a functional dendrogram. Various characteristics of FD make it preferable to other measures of functional diversity, such as the number of functional groups in a community. Simulating species' trait values illustrates how the relative importance of richness and composition for FD depends on the effective dimensionality of the trait space in which species separate. Fewer dimensions increase the importance of community composition and functional redundancy. More dimensions increase the importance of species richness and decreases functional redundancy. Clumping of species in trait space increases the relative importance of community composition. Five natural communities show remarkably similar relationships between FD and species richness.
1. The goal of this research was to identify indigenous tree species with a positive influence on soil fertility, in order to design mixed-tree and tree/crop systems for the Atlantic forest region of Bahia, Brazil. The study focused on 20 native tree species growing in 14-15-year-old stands in an arboretum at Pau Brasil Ecological Station. Although the small size of the areas sampled and the lack of adequate replication limits the interpretation of the results, the pure tree stands offered a unique opportunity to evaluate the nutrient cycling characteristics of several species which could be useful for their future utilization in land rehabilitation systems. 2. Soils for chemical analysis and bulk density were sampled under a 25-year-old secondary forest, a mixed-species plantation, the native forest and under the 20 species in question. Forest-floor litter and live leaf samples were analysed for N, P, K, Ca, Mg and Al. 3. Soil fertility was higher in secondary than in primary forest. The mixed plantation had similar soil pH, C, N and Mg, slightly higher P, and lower K and Ca than the primary forest. Litter accumulation on the floor was larger in secondary than in primary forest. Litter nutricnts were also higher in secondary than in primary forest. 4. Positive effects on soils were noted under 15 out of the 20 species studied, among those Inga affinis, Parapiptadenia pterosperma (N-fixing species); Arapatiella psilophylla, Caesalpinia echinata, (leguminous, non-N-fixing); Eschweilera ovata, Lecythis pisonis, Licania hypoleuca (of other families). 5. Among the 20 species in the arboretum, the highest dry weights of forest-floor litter were found under Arapatiella psilophylla, Bombax macrophyllum, Inga affinis, Licania hypoleuca and Pithecellobium pedicellare; positive effects on soils were found under all these species, with P. pedicellare having the least influence. This suggests that forest-floor nutrients were incorporated in the soil via decomposition under these species. 6. Species that contribute to increased C and N, such as Caesalpinia echinata, Inga affinis, Parapiptadenia pterosperma and Plathymenia foliolosa, could be combined with those that increase soil pH, basic cations or both, such as Copaifera luscens, Eschweilera ovata, Lecythis pisonis and Licania hypoleuca. The inclusion of Arapatiella psilophylla, Bombax macrophyllum, Buchenavia grandis, Caesalpinia echinata, Cassia spp., Hymenaea aurea and Inga affinis could contribute to increased levels of extractable P in the surface soils. In addition to their potential effects on soil fertility, species choices must be guided by seed and seedling availability, as well as by farmers' preferences, local uses for the species and economic aspects (cost of establishment and market potential).
Summary •For biological community data (species-by-sample abundance matrices), Warwick & Clarke (1995) defined two biodiversity indices, capturing the structure not only of the distribution of abundances amongst species but also the taxonomic relatedness of the species in each sample. The first index, taxonomic diversity (), can be thought of as the average taxonomic ‘distance’ between any two organisms, chosen at random from the sample: this distance can be visualized simply as the length of the path connecting these two organisms, traced through (say) a Linnean or phylogenetic classification of the full set of species involved. The second index, taxonomic distinctness (*), is the average path length between any two randomly chosen individuals, conditional on them being from different species. This is equivalent to dividing taxonomic diversity, , by the value it would take were there to be no taxonomic hierarchy (all species belonging to the same genus). * can therefore be seen as a measure of pure taxonomic relatedness, whereas mixes taxonomic relatedness with the evenness properties of the abundance distribution. •This paper explores the statistical sampling properties of and *. Taxonomic diversity is seen to be a natural extension of a form of Simpson's index, incorporating taxonomic (or phylogenetic) information. Importantly for practical comparisons, both and * are shown not to be dependent, on average, on the degree of sampling effort involved in the data collection; this is in sharp contrast with those diversity measures that are strongly influenced by the number of observed species. •The special case where the data consist only of presence/absence information is dealt with in detail: and * converge to the same statistic (+), which is now defined as the average taxonomic path length between any two randomly chosen species. Its lack of dependence, in mean value, on sampling effort implies that + can be compared across studies with differing and uncontrolled degrees of sampling effort (subject to assumptions concerning comparable taxonomic accuracy). This may be of particular significance for historic (diffusely collected) species lists from different localities or regions, which at first sight may seem unamenable to valid diversity comparison of any sort. •Furthermore, a randomization test is possible, to detect a difference in the taxonomic distinctness, for any observed set of species, from the ‘expected’+ value derived from a master species list for the relevant group of organisms. The exact randomization procedure requires heavy computation, and an approximation is developed, by deriving an appropriate variance formula. This leads to a ‘confidence funnel’ against which distinctness values for any specific area, pollution condition, habitat type, etc., can be checked, and formally addresses the question of whether a putatively impacted locality has a ‘lower than expected’ taxonomic spread. The procedure is illustrated for the UK species list of free-living marine nematodes and sets of samples from intertidal sites in two localities, the Exe estuary and the Firth of Clyde.
For more than a century, scientists have considered whether mixtures of tree species may differ in nutrition and yield relative to monocultures. We review the empirical evidence on the nutritional interactions of tree species in mixtures, including information on foliar nutrition, soil nutrient supply, rates of nutrient input, and patterns of root dis - tribution. Linear effects were most common, with mixtures intermediate in value between monocultures. In some cases, values for mixtures were lower than expected, indicating an antagonistic interaction. A few cases that included nitrogen- fixing species showed a synergistic interaction, with mixtures showing higher values than monocultures. Nutrient con - centrations in foliage of Sitka spruce (Picea sitchensis (Bong.) Carrière) were improved in mixtures with other conifers in three studies, in contrast to four studies with mixtures of various conifers and hardwoods that showed no effect of mixtures on foliage nutrient concentrations. Mixtures that combine species with and without the ability to fix atmo - spheric nitrogen have shown a full range of foliar responses from decreases to increases in phosphorus, to increases in nitrogen, to no effect of mixtures. Rates of litter decomposition usually showed no effect of species mixtures, but a few cases demonstrated both increases and decreases in decomposition relative to monocultures. Pools of soil nutrients generally did not differ between mixtures and monocultures. Root distributions in mixtures of Norway spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) were altered in mixtures; compared with monocultures, spruce rooted more shallowly in mixtures with beech, and beech rooted more deeply in mixtures with spruce. General conclusions are limited by the small number of studies that directly addressed mixed-species effects in forests, and the wide variety of observed interactions. Further research would be particularly helpful in identifying situations where nonlinear inter- actions may develop, including the species and site conditions that promote nonlinear interactions. Neighborhood meth- ods, which analyze the relationship between stand composition and nutritional properties on a small spatial scale, offer great potential for exploring nutritional effects in mixed-species stands.
When pairwise differences (relatedness) between species are numerically given, the average of the species differences weighted by relative frequencies can be used as a species diversity index. This paper first theoretically develops the indices of this type, then applies them to forestry data. As examples of diversity indices, this paper explores the taxonomic diversity and the newly introduced amino acid diversity, which is a modification of the nucleotide diversity in genetics. The first, mathematical part shows that both indices can be decomposed into three inner factors; evenness of relative frequencies (=the Simpson index), the simple average over species differences regardless of relative frequencies, and the taxonomic or genetic balance in relative frequencies. The taxonomic diversity has another decomposition: the sum over the Simpson indices at all the taxonomic levels. The second part examines the effects of different forest management techniques on diversity. It is shown that a thinning operation for promoting survival of specific desirable species also contributed to increasing the taxonomic diversity. If we calculated only conventional indices that do not incorporate species relatedness, we would simply conclude that the thinning did not significantly affect the diversity. The theoretical developments of the first part complement the result, leading us to a better interpretation about contrasting vegetation structures. The mathematical results also reveal that the amino acid diversity involves redundant species, which is undesirable when measuring diversity; hence, this index is used to demonstrates crucial points when we introduce species relatedness. The results suggest further possibilities of applying diversity indices incorporating species differences to a variety of ecological studies.
Functional diversity is a component of biodiversity that generally concerns the range of things that organisms do in communities and ecosystems. Here, we review how functional diversity can explain and predict the impact of organisms on ecosystems and thereby provide a mechanistic link between the two. Critical points in developing predictive measures of functional diversity are the choice of functional traits with which organisms are distinguished, how the diversity of that trait information is summarized into a measure of functional diversity, and that the measures of functional diversity are validated through quantitative analyses and experimental tests. There is a vast amount of trait information available for plant species and a substantial amount for animals. Choosing which traits to include in a particular measure of functional diversity will depend on the specific aims of a particular study. Quantitative methods for choosing traits and for assigning weighting to traits are being developed, but need much more work before we can be confident about trait choice. The number of ways of measuring functional diversity is growing rapidly. We divide them into four main groups. The first, the number of functional groups or types, has significant problems and researchers are more frequently using measures that do not require species to be grouped. Of these, some measure diversity by summarizing distances between species in trait space, some by estimating the size of the dendrogram required to describe the difference, and some include information about species abundances. We show some new and important differences between these, as well as what they indicate about the responses of assemblages to loss of individuals. There is good experimental and analytical evidence that functional diversity can provide a link between organisms and ecosystems but greater validation of measures is required. We suggest that non-significant results have a range of alternate explanations that do not necessarily contradict positive effects of functional diversity. Finally, we suggest areas for development of techniques used to measure functional diversity, highlight some exciting questions that are being addressed using ideas about functional diversity, and suggest some directions for novel research.
The mass of fine litterfall and nutrient circulation through litterfall were determined in four Melrosideros polymorpha/Cibotium spp.-dominated rainforests that differed in substrate age, parent material texture and annual precipitation on Kilauea and Mauna Loa volcanoes on the island of Hawaii. Three of the sites had rates of litterfall of 5.2 Mg ha−1 y−1; the fourth, which was on the most fertile soil, produced 7.0 Mg ha−1 y−1 of litterfall with higher concentrations of nitrogen and phosphorus. Tree ferns of the genus Cibotium cycled relatively large amounts of nitrogen, phosphorus and potassium through litterfall; their contribution to nutrient circulation was disproportionate to their mass in the forest, or in litterfall. The forest on the youngest substrate, which also had the lowest concentrations of nitrogen in litterfall, was fertilized with complete factorial combinations of nitrogen, phosphorus and a treatment consisting of all other plant nutrients. Additions of nitrogen increased the quantity and nitrogen concentration in litterfall during the second year following the initiation of fertilization, while no other treatment had a significant effect. Additions of nitrogen had no effect on litterfall mass or nutrient concentrations in the most nutrient-rich site.
For biological community data (species‐by‐sample abundance matrices), Warwick & Clarke (1995) defined two biodiversity indices, capturing the structure not only of the distribution of abundances amongst species but also the taxonomic relatedness of the species in each sample. The first index, taxonomic diversity (δ), can be thought of as the average taxonomic ‘distance’ between any two organisms, chosen at random from the sample: this distance can be visualized simply as the length of the path connecting these two organisms, traced through (say) a Linnean or phylogenetic classification of the full set of species involved. The second index, taxonomic distinctness (δ * ), is the average path length between any two randomly chosen individuals, conditional on them being from different species. This is equivalent to dividing taxonomic diversity, δ, by the value it would take were there to be no taxonomic hierarchy (all species belonging to the same genus). δ * can therefore be seen as a measure of pure taxonomic relatedness, whereas δ mixes taxonomic relatedness with the evenness properties of the abundance distribution.
This paper explores the statistical sampling properties of δ and δ * . Taxonomic diversity is seen to be a natural extension of a form of Simpson's index, incorporating taxonomic (or phylogenetic) information. Importantly for practical comparisons, both δ and δ * are shown not to be dependent, on average, on the degree of sampling effort involved in the data collection; this is in sharp contrast with those diversity measures that are strongly influenced by the number of observed species.
The special case where the data consist only of presence/absence information is dealt with in detail: δ and δ * converge to the same statistic (δ ⁺ ), which is now defined as the average taxonomic path length between any two randomly chosen species. Its lack of dependence, in mean value, on sampling effort implies that δ ⁺ can be compared across studies with differing and uncontrolled degrees of sampling effort (subject to assumptions concerning comparable taxonomic accuracy). This may be of particular significance for historic (diffusely collected) species lists from different localities or regions, which at first sight may seem unamenable to valid diversity comparison of any sort.
Furthermore, a randomization test is possible, to detect a difference in the taxonomic distinctness, for any observed set of species, from the ‘expected’δ ⁺ value derived from a master species list for the relevant group of organisms. The exact randomization procedure requires heavy computation, and an approximation is developed, by deriving an appropriate variance formula. This leads to a ‘confidence funnel’ against which distinctness values for any specific area, pollution condition, habitat type, etc., can be checked, and formally addresses the question of whether a putatively impacted locality has a ‘lower than expected’ taxonomic spread. The procedure is illustrated for the UK species list of free‐living marine nematodes and sets of samples from intertidal sites in two localities, the Exe estuary and the Firth of Clyde.
This paper stresses that the mechanism of coexistence is the key to understanding the relationship between species richness and community productivity. Using model plant communities, we explored two general kinds of mechanisms based on resource heterogeneity and recruitment limitation, with and without any trade-off between reproductive and competitive abilities. We generated different levels of species richness by changing model parameters, in particular the number of species in the regional pool, the degree of recruitment limitation, and the level of heterogeneity. Different diversity–productivity patterns are obtained with different coexistence mechanisms, indicating there is no reason to expect any general relationship between species richness and productivity. We discuss these results in the context of the within-site and across-site aspects of the relationship between species richness and productivity. Furthermore, we extend these results to hypothesize the relationship between species richness and productivity for other coexistence mechanisms not explicitly considered here.
Question
Is Rao's quadratic entropy a suitable measure of functional diversity if several traits are considered?
Methods
It is checked whether Rao's quadratic entropy ( FD Q ) satisfies a priori criteria suggested by Mason et al. A real data set is used to show that there are often zeros in abundance distributions which maximize functional diversity.
Results and Conclusion
FD Q fulfils all a priori criteria and it surpasses other proposed indices, because it includes species abundances and more than one trait. Therefore, it seems to be an improvement compared to measures of functional diversity that are currently available. An unexpected property of FD Q is that its value may decrease if species richness increases. The reason is that functional diversity is influenced by both species‐abundance based diversity and differences among species. Introduction of a new species into the community increases the species‐abundance based diversity, while it may decrease the average dissimilarity among species.
There is currently much interest in understanding how loss of biodiversity might alter ecological processes vital to the functioning of ecosystems. Unfortunately, ecologists have reached little consensus regarding the importance of species diversity to ecosystem functioning because empirical studies have not demonstrated any consistent relationship between the number of species in a system and the rates of ecological processes. We present the results of a simple model that suggests there may be no single, generalizable relationship between species diversity and the productivity of an ecosystem because the relative contributions of species to productivity change with environmental context. The model determined productivity for landscapes varying in species diversity (the number of species in the colonist pool), spatial heterogeneity (the number of habitat types composing the landscape), and disturbance regimes (+/− a non-selective mortality). Linear regressions were used to relate species diversity and productivity for each of the environmental contexts. Disturbance changed the form of the diversity/productivity relationship by reducing the slope (i.e. the change in productivity per species added to the colonist pool), but spatial heterogeneity increased or decreased this slope depending on the particular habitat types composing the landscape. The cause of the diversity/productivity relationship also changed with environmental context. The amount of variation in productivity explained by species diversity always increased with spatial heterogeneity, while the amount of variation explained by species composition (i.e. the particular species composing the colonist pool) tended to increase with disturbance. These results lead us to conclude that the form and cause of the relationship between species diversity and productivity may be highly dynamic-changing over both time and space. Because the trends resulted from well-known mechanisms by which environmental variation alters the absolute and relative abundances of taxa, we suspect this conclusion may be applicable to many different systems.
Characterization of decomposition characteristics is important for sound management of organic residues for both soils and
livestock, but routine residue quality analysis is hindered by slow and costly laboratory methods. This study tested the accuracy
and repeatability of near-infrared spectroscopy (NIR) for direct prediction of in vitro dry matter digestibility (IVDMD) and C and N mineralization for a diverse range of organic materials (mostly crop and tree
residues) of varying quality (n=32). The residue samples were aerobically incubated in a sandy soil and amounts of C and N mineralized determined after
28days. IVDMD and quality attributes were determined using wet chemistry methods. Repeatability was higher with NIR than
the original wet chemistry methods: on average NIR halved the measurement standard deviation. NIR predicted IVDMD and C and
N mineralization more accurately than models based on wet chemical analysis of residue quality attributes: reduction in root
mean square error of prediction with NIR, compared with using quality attributes, was IVDMD, 6%; C mineralization after 28days,
8%; and N mineralization after 28days, 8%. Cross-validated r
2 values for measured wet chemistry vs. NIR-predicted values were: IVDMD, 0.88; C mineralization, 0.82; and N mineralization,
0.87. Direct prediction of decomposition and mineralization from NIR is faster, more accurate and more repeatable than prediction
from residue quality attributes determined using wet chemistry. Further research should be directed towards establishment
of diverse NIR calibration libraries under controlled conditions and direct calibration of soil quality, crop and livestock
responses in the field to NIR characteristics of residues.
The role of residue characteristics in enhancing the availability of P was investigated in a greenhouse study using two soils from the northern Guinea savanna (NGS) and four from the derived savanna (DS) zones of the West African moist savanna. Eight organic residues of varying C-to-P ratio were used and maize ( Zea mays) was grown for 7weeks. The effect of the organic residues on P availability (measured as resin P and maize P accumulation) differed among the soils. On average, the increase in resin P, calculated as {[(soil+residue)–control]/(control)100}, was between 8% (Davi, DS) and 355% (Danayamaka, NGS). Maize P accumulation was increased by ca. 11% in Davi and Niaouli (DS) soils and 600% in Danayamaka soil. The increase in maize total dry matter yield (DMY) ranged from 2% to 649%. Residues with C-to-P ratio >200 produced lower DMY than those with lower ratios. Residue organic P (Po) extractable with 0.2N H2SO4 (acid-Po) accounted for 92% ( P =0.0001) of the variation in DMY in a step-wise regression with residue parameters as independent variables and mean DMY as the dependent variable. The residue Po extractable with 0.5M NaHCO3 (HCO3-Po) correlated significantly with DMY in Danayamaka and Davi soils, and with P accumulation in Danayamaka soil. The relationships between the residue Po and DMY might imply that Po fractions in decomposing residues contribute to P availability. However, the suitability of using the Po content of organic residues to predict their agronomic value with respect to P nutrition needs further evaluation.
We explore empirical and theoretical evidence for the functional significance of plant-litter diversity and the extraordinary high diversity of decomposer organisms in the process of litter decomposition and the consequences for biogeochemical cycles. Potential mechanisms for the frequently observed litter-diversity effects on mass loss and nitrogen dynamics include fungi-driven nutrient transfer among litter species, inhibition or stimulation of microorganisms by specific litter compounds, and positive feedback of soil fauna due to greater habitat and food diversity. Theory predicts positive effects of microbial diversity that result from functional niche complementarity, but the few existing experiments provide conflicting results. Microbial succession with shifting enzymatic capabilities enhances decomposition, whereas antagonistic interactions among fungi that compete for similar resources slow litter decay. Soil-fauna diversity manipulations indicate that the number of trophic levels, species identity, and the presence of keystone species have a strong impact on decomposition, whereas the importance of diversity within functional groups is not clear at present. In conclusion, litter species and decomposer diversity can significantly influence carbon and nutrient turnover rates; however, no general or predictable pattern has emerged. Proposed mechanisms for diversity effects need confirmation and a link to functional traits for a comprehensive understanding of how biodiversity interacts with decomposition processes and the consequences of ongoing biodiversity loss for ecosystem functioning.
One year field exposures of leaf litter from replicated plots of Pinus caribaea var. hondurensis Barrett and Golfari, Carapa guianensis Aubl., Euxylophora paraensis Hub., a Leguminosae combination (Dalbergia nigra Fr. All., Dinizia excelsa Ducke, Parkia multijuga Benth.), and adjacent upland (terra firme) forest at the Curuá-Una Forest Reserve, Pará, Brazil were used to examine the factors controlling leaf litter decay and N dynamics in a lowland tropical environment. Initial leaf litter N concentrations ranged from 4.4 (P. caribaea) to 16.3 mg g−1 dry matter (Leguminosae), and initial lignin concentrations from 190.8 (Leguminosae) to 459.3 mg g−1 dry matter (forest). Pinus caribaea leaf litter lost the least mass (28%), and the Leguminosae leaf litter the most (61%), during the year long incubations. Initial and 1-y proximate C fractions, N concentrations and polyphenol concentrations were not related to mass loss. Annual N accumulation or depletion from leaf litter under the plantations and forest was related to C loss (R2=0.93, P=0.007) and holocellulose loss (R2=0.84, P=0.02). When leaf litter was placed outside its stand of origin, there was a significant location effect on decay rates, indicating that differences in the physical and biological microenvironments under the monospecific plots affected litter decomposition.
Interactions between biotic and abiotic processes complicate the design and interpretation of ecological experiments. Separating causality from simple correlation requires distinguishing among experimental treatments, experimental responses, and the many processes and properties that are correlated with either the treatments or the responses or both. When an experimental manipulation has multiple components, but only one of them is identified as the experimental treatment, erroneous conclusions about cause and effect relationships are likely because the actual cause of any observed response may be ignored in the interpretation of the experimental results. This unrecognised cause of an observed response can be considered a "hidden treatment". Three types of hidden treatments are potential problems in biodiversity experiments:
(1) abiotic conditions, such as resource levels, or biotic conditions, such as predation, which are intentionally or unintentionally altered in order to create differences in species numbers for"diversity" treatments;
(2) non-random selection of species with particular attributes that produce treatment differences that exceed those due to "diversity" alone;
(3) the increased statistical probability of including a species with dominant negative or positive effect (e.g. dense shade, or nitrogen fixation) in randomly selected groups of species of increasing number or "diversity".
In each of these cases, treatment responses that are actually the result of the "hidden treatment" may be inadvertently attributed to variation in species number. Case studies re-evaluating three different types of biodiversity experiments demonstrate that the increases found in such ecosystem properties as productivity, nutrient use efficiency, and stability (all of which were attributed to higher level of species diversity) were actually caused by "hidden treatments" that altered plant biomass and productivity.
The objective of this research was to determine whether diffuse reflectance calibrations using a Fourier transform spectrometer (FTS) could be improved by increasing the scanned sample area. A linear motion sample transport (TRANSCELL) was attached to the FTS, which increased the area scanned from 2 mm in diameter (stationary cell or STATCELL) to 2 × 50 mm. Sodium chlorite-treated forages and by-products (N = 174) were scanned in the near-infrared (NIR) and mid-infrared (MIR) with the use of the TRANSCELL and STATCELL. Samples were analyzed for fiber, digestibility, lignin, protein, and lignin nitrobenzene oxidation products (NOPs). Overall, the best results for fiber, lignin, and digestibility were achieved by using MIR spectra and the TRANSCELL. Results in the NIR (FTS) with the use of the TRANSCELL were also improved over those obtained with the STATCELL. While the TRANSCELL was an improvement over the STATCELL for Fourier NIR analysis of NOPs, in the MIR, results for NOPs were about equal for the TRANSCELL and STATCELL. In conclusion, the use of a TRANSCELL can improve calibrations from Fourier transform spectrometers, although the degree of improvement depends on the spectral region and specific calibration under study.
A detailed quantitative description is given of the tree flora of thirty-eight square plots of 10 × 10 m in four forest-types at c. 1550 m altitude on the ridge between John Crow Peak and Morce's Gap in the Blue Mountains in Jamaica. The four forest-types (Mor Ridge, Mull Ridge, Wet Slope and Gap) can be assigned to three associations: the Chaetocarpus globosus--Clusia cf. havetioides--Lyonia cf. octandra association (Mor Ridge), the Dendropanax pendulus-Hedyosmum arborescens-Podocarpus urbanii association (Mull Ridge and Wet Slope) and the Cyathea pubescens--Meriania purpurea--Solanum punctulatum association (Gap). The two Ridge forests have a higher basal area and more individuals per unit area than the Gap and Wet Slope forests. The distributions of individuals in girth size-classes show that most species are regenerating. The level of competition appears to fall in the sequence Gap > Mull Ridge > Mor Ridge and to be greater in Gap forest than Wet Slope forest. The amount of organic matter in the soil decreases in the series Mor Ridge > Mull Ridge > Gap > Wet Slope. In a mineralization test moderate quantities of nitrate were released in all soils except that of the Wet Slope forest. In a series of bioassays several species were found to fail completely on Mor Ridge forest soil. Two species showed a primary limitation by phosphorus on the other three soils, and one accumulated nitrogen to high levels. Holcus lanatus on soil from Mor Ridge forest showed a significant response to phosphate fertilizers but only after the pH was raised. Mean foliar levels of N, P, K and Ca increase along the sequence Mor Ridge, Mull Ridge-cum-West Slope, Gap. In contrast, the foliar levels in single species do not differ between forest-types except for K and Mg; the K level is markedly lower in Mor Ridge forest. It is tentatively suggested that the Mor Ridge forest is limited primarily by the extremely low soil pH (2.8-3.5), that the Mull Ridge forest is limited relative to the Gap forest by a slower circulation of nutrients, and that the Wet Slope forest is limited relative to Mull Ridge forest by the lack of support provided by the very shallow soil ( \geqslantless 30 cm deep) and the difficulty of establishment on a 30°-slope. Comparisons between the Jamaican forests and Lower Montane Rain forests in Puerto Rico and New Guinea show that the Jamaican forest soils are all low in total carbon (except Mor Ridge soil), total nitrogen and instantaneously exchangeable bases. Comparison of mean foliar mineral levels between the most widespread Jamaican forest-type (Mull Ridge-cum-Wet Slope) and a much taller Lower Montane Rain forest in New Guinea suggests that the Jamaican forest is not short of N, P, K or Ca, but it is emphasized that more critical studies on mineral cycling are needed to explore this question.
There has been a rapidly increasing recent interest in the effects of biological diversity on ecosystem properties, and while some studies have recently concluded that biodiversity improves ecosystem function, these views are based almost entirely on experiments in which species richness of live plants has been varied over all the species diversity treatments. However, most net ecosystem primary productivity eventually enters the decomposition subsystem as plant fitter where it has important ''afterlife effects''. We conducted a field experiment in which litter from 32 plant species (i.e. eight species of each of four plant ''functional groups'' with contrasting litter quality) was collected and placed into litter-bags so that each litter-bag contained between one and eight species; the species which were included in the multiple (greater than or equal to 2) species litter-bags were randomly selected. This litter diversity gradient was created within each functional group and across some functional groups. We found large non-additive effects of mixing litter from different species on litter decomposition rates, litter nitrogen contents, rates of nitrogen release from litter and the active microbial biomass present on the litter. The patterns and directions of these non-additive effects were dependent upon both plant functional group and lime of harvest, and these effects could be predicted in some instances by the initial litter nitrogen content and the degree of variability of nitrogen content of the component species in the litter-bag. There was no relationship between litter-bag species richness and any of the response variables that we considered, at least between two and eight species. Within plant functional groups our results provide some support for the species redundancy and idiosyncratic hypotheses about how biodiversity alters ecosystem function, but no support for the ecosystem rivet hypothesis or the view that species richness of plant litter is important for ecosystem function. We suggest that increased species diversity of plant litter is less important than that of live plants for determining ecosystem properties (and provide possible reasons for this) and conclude that perceived relationships between biodiversity and ecosystem function may be of diminished significance when the ecological importance of plant litter is fully appreciated.
Previous studies on biodiversity and soil food web composition have mentioned plant species identity, as well as plant species diversity as the main factors affecting the abundance and diversity of soil organisms. However, most studies have been carried out under limitations of time, space, or appropriate controls. In order to further examine the relation between plant species diversity and the soil food web, we conducted a three-year semi-field experiment in which eight plant species (4 forb and 4 grass species) were grown in monocultures and mixtures of two, four and eight plant species. In addition there were communities with 16 plant species. We analyzed the abundance and identity of the nematodes in soil and roots, including feeding groups from various trophic levels (primary and secondary consumers, carnivores, and omnivores) in the soil food web.
Plant species diversity and plant identity affected the diversity of nematodes. The effect of plant diversity was attributed to the complementarity in resource quality of the component plant species rather than to an increase in total resource quantity. The nematode diversity varied more between the different plant species than between different levels of plant species diversity, so that plant identity is more important than plant diversity. Nevertheless the nematode diversity in plant mixtures was higher than in any of the plant monocultures, due to the reduced dominance of the most abundant nematode taxa in the mixed plant communities. Plant species identity affected the abundances of the lower trophic consumer levels more than the higher trophic levels of nematodes. Plant species diversity and plant biomass did not affect nematode abundance. Our results, therefore, support the hypothesis that resource quality is more important than resource quantity for the diversity of soil food web components and that plant species identity is more important than plant diversity per se.
The objective of this research was to determine whether diffuse reflectance calibrations using a Fourier transform spectrometer (FTS) could be improved by increasing the scanned sample area. A linear motion sample transport (TRANSCELL) was attached to the FTS, which increased the area scanned from 2 mm in diameter (stationary cell or STATCELL) to 2 X 50 mm. Sodium chlorite-treated forages and by-products (N = 174) were scanned in the near-infrared (NIR) and mid-infrared (MIR) with the use of the TRANSCELL and STATCELL. Samples were analyzed for fiber, digestibility, lignin, protein, and lignin nitrobenzene oxidation products (NOPs). Overall, the best results for fiber, lignin, and digestibility were achieved by using MIR spectra and the TRANSCELL. Results in the NIR (FTS) with the use of the TRANSCELL were also improved over those obtained with the STATCELL. While the TRANSCELL was an improvement over the STATCELL for Fourier NIR analysis of NOPs, in the MIR, results for NOPs were about equal for the TRANSCELL and STATCELL. In conclusion, the use of a TRANSCELL can improve calibrations from Fourier transform spectrometers, although the degree of improvement depends on the spectral region and specific calibration under study.
Funktionelle Diversität wurde als ein Schlüssel zum Verständnis von Ökosystemprozessen, wie Produktivität, Nährstoffkreislauf und –speicherung, Kohlenstoffsequestration und Stabilität gegenüber Störung betrachtet. Dennoch ist immer noch unklar, wie funktionelle Diversität gemessen werden sollte. In dieser Veröffentlichung schlage ich eine Anzahl fundamentaler Kriterien vor, die ein bedeutsamer Index der funktionellen Diversität erfüllen sollte, damit er sich in der ökologischen Forschung vernünftig verwenden lässt. Wenn die funktionelle Diversität über die paarweisen funktionellen Distanzen zwischen den Arten einer gegebenen Ansammlung berechnet wird, sollten die in Frage kommenden Maße monoton sein, monoton hinsichtlich der Distance, und sie sollten die “twinning”-Bedingang (Weitzmann 1992) erfüllen. Auf der anderen Seite, wenn die funktionelle Diversität unter Berücksichtigung sowohl der paarweisen funktionellen Distanzen zwischen den Arten als auch ihren relativen Abundanzen berechnet wird, sollte das in Frage kommende Maß konkav sein, und so die additive Auftrennung der Diversität in αα- ββ- und γγ-Größen erlauben. Konformität mit den oben genannten Anforderungen könnte bei der Auswahl einer Familie von Maßen hilfreich sein, die am besten geeignet sind für eine korrekte Evaluation der Beziehungen zwischen biologischer Diversität und Ökosystemfunktion.
As studied at the Hubbard Brook Experimental Forest, rate constants (k) for annual leaf mass loss ranged from -0.08 to - 0.47. The rate constants had a negative linear correlation with the ratio of initial lignin concentration to initial N concentration. Decomposition dynamics of the litter materials were described by inverse linear relationships between the percentage of original mass remaining and the N concentration in the residual material. Initial lignin concentration was highly correlated with the slope of the inverse linear relationship for each of the litter types. -from Authors
Despite its importance for the understanding of element cycles in ecosystems, organic matter (OM) quality has remained an elusive property that is difficult to measure. In this study; two new approaches, both of which taking into account the complete biochemical composition of the organic material during the decomposition process, have been combined to solve this problem. First, following the continuous-quality theory where quality is defined as a measure of substrate availability to the decomposers, initial litter OM qualities of a range of plant species From two experiments on litter decomposition were estimated and resulted in highly accurate fits of observed mass loss during decomposition. Applying the same theory, dualities of the litters at all stages of decomposition were then calculated. By comparison, the initial qualities of the same litters were estimated from conventional chemical fractions and resulted in much lower accurate fits. Second, near-infrared reflectance spectroscopy (NIRS), a highly precise physical method of characterising biochemical composition of OM, was used to obtain a unique spectral signature of each sample. Calibrations were performed between spectral data and calculated qualities on the first half of the sample set and the calibration equations were applied to the second half of the sample set. Results show that theoretical litter OM quality can be calibrated and predicted precisely using NIRS. OM quality, defined according to a theoretical concept of substrate availability to decomposers, then contains and summarises all the relevant biochemical information. We demonstrate how the combination of NIRS and theory allows us to accurately measure OM quality. Measurement of OM quality provides an access to a fundamental property of organic matter and opens up new possibilities for studying element cycles in ecosystems.
Microarthropods have a variable but generally significant effect on litter disappearance and therefore on detrital standing crops. An average increase in litter decomposition rates of 23% was noted for 15 studies that ranged from 9-30 months in duration. Increased mineralization of N, P and K was seen in only about half of those studies reporting microarthropod effects on nutrient dynamics. Mass loss is more affected than are nutrients owing to stimulation of microbial respiration by microarthropods. This respiration results in carbon mineralization but converts other elements into microbial tissues, most of which is recycled within the detritus. Mineralization of N, P and cations will probably increase in older litter as a result of microarthropod feeding activities. Directions for future research are indicated.-from Author
Decomposition of leaf litter was surveyed during the ®rst nine months of decomposition in the ®eld. At three woodland sites that differ with respect to leaf litter species richness, as well as to microbial activity and the abundance of terrestrial isopods, being the most numerous representatives of the saprophagous macrofauna at these sites, changes in the chemical composition of the mixed leaf litter were monitored on a three-monthly basis. Six out of seven leaf litter compounds exhibited changes in their contents that were positively correlated with high microbial activity and/or high isopod abundance during decomposition. Further, site characteristics other than soil pH, water holding capacity (WHC) or percent sand, signi®cantly explained the variance in decomposition of ®ve different chemical compounds, as well as the overall mass loss of leaf litter. These site characteristics include the site-speci®c species richness of the litter layer. At the site with low microbial activity and low isopod numbers but a leaf litter mixture of nine species, decomposition did not proceed more slowly than at that site with high microbial activity and high isopod abundance but leaf litter made up by only ®ve species. From these results, I hypothesize that a diverse vegetation, resulting in leaf litter of high species richness, promotes decomposition processes, and thus nutrient recycling. q 2002 Published by Elsevier Science Ltd.
A general coefficient measuring the similarity between two sampling units is defined. The matrix of similarities between all pairs of sample units is shown to be positive semidefinite (except possibly when there are missing values). This is important for the multidimensional Euclidean representation of the sample and also establishes some inequalities amongst the similarities relating three individuals. The definition is extended to cope with a hierarchy of characters.
Literature on plant leaf litter decomposition is substantial, but only in recent years have potential interactions among leaves of different species during decomposition been examined. We review emerging research on patterns of mass loss, changes in nutrient concentration, and decomposer abundance and activity when leaves of different species are decaying in mixtures. Approximately 30 papers have been published that directly examine decomposition in leaf mixtures as well as in all component species decaying alone. From these litter-mix experiments, it is clear that decomposition patterns are not always predictable from single-species dynamics. (Characteristics of decomposition in litter-mixes that deviate from responses predicted from decomposition of single-species litters alone are designated "non-additive"; "additive" responses in mixes are predictable from component species decaying alone.) Non-additive patterns of mass loss were observed in 67% of tested mixtures; mass loss is often (though not always) increased when litters of different species are mixed. Observed mass loss in some mixtures is as much as 65% more extensive than expected from decomposition of single-species litter, but more often mass loss in mixtures exceeds expected decay by 20% or less. Nutrient transfer among leaves of different species is striking, with 76% of the mixtures showing non-additive dynamics of nutrient concentrations. Non-additive patterns in the abundance and activity of decomposers were observed in 55% and 65% of leaf mixes, respectively. We discuss some methodological details that likely contribute to conflicting results among mixed-litter studies to date. Enough information is available to begin formulating mechanistic hypotheses to explain patterns in litter-mix experiments. Emerging patterns in the mixed-litter decomposition literature have implications for relationships between biodiversity and ecosystem function (in this case, the function being decomposition), and for potential mechanisms through which invasive plant species could alter carbon and nutrient dynamics in ecosystems.
Plant species litter mixtures often result in nonadditive differences in eco-system processes when compared to the average of their individual components. However, these studies are just beginning to be extended to the genotype level and to our knowledge have not incorporated the effects of herbivory or genotype-by-herbivore interactions. With a two-year field study, using genotypes that differed by as few as three restriction length polymorphism (RFLP) molecular markers, we found three major patterns when we mixed leaf litters from different genotypes both with and without previous herbivory. First, leaf litter genotype mixtures, regardless of herbivory, demonstrated nonadditive rates of de-composition and nutrient flux. Second, mixed genotype litter without herbivory decomposed faster than the same genotypes with herbivory. Third, in genotype mixtures, with and without herbivory, we found that net rates of immobilization of both nitrogen and phosphorus can differ from expected values (based on genotype means) by as much as 57%. These results show that mixing litter genotypes can alter rates of decay and nutrient flux and that the effects are reduced with herbivory. Nonadditive effects at the genotype level that we report here are nearly as large as what has been recorded for plant species mixtures and may have important, though under-appreciated, roles in ecosystems. These data further suggest that genetic diversity and genotype-by-herbivore interactions can affect fundamental ecosystem processes such as litter decomposition and nutrient flux.
Human disturbances both decrease the number of species in ecosystems and change their relative abundances. Here we present field evidence demonstrating that shifts in species abundances can have effects on ecosystem functioning that are as great as those from shifts in species richness. We investigated spatial and temporal variability of leaf decomposition rates and community metrics of leaf-eating invertebrates (shredders) in streams. The shredder community composition dramatically influenced the diversity–function relationship; decomposition was much higher for a given species richness at sites with high species dominance than at sites where dominance was low. Decomposition rates also markedly depended on the identity of the dominant species. Further, dominance effects on decomposition varied seasonally and the number of species required for maintaining decomposition increased with increasing evenness. These findings reveal important but less obvious aspects of the biodiversity–ecosystem functioning relationship.
In recent decades numerous diversity indices have been introduced. Among them the quadratic entropy index Q expresses the mean difference between two individuals chosen from the community at random. Differing from diversity indices habitually employed, Q does not satisfy a property postulated earlier for those measures. Namely, the uniform distribution of species does not necessarily yield the maximal index value. Q is based on the difference matrix of species. For a given matrix one can seek for the vector yielding the maximum quadratic entropy. This task leads to a quadratic programming problem. Using the appropriate program of a program package, we determined the maximum vector for a genetic difference matrix of crane species, as published in the literature. We discovered that some components (frequencies) in the maximum vector are equal to zero. That is, by maximizing the quadratic diversity some species can be eliminated. We discuss briefly the possible implications of this observation. Moreover, even if all elements in the maximum vector are positive, the elements can differ.
This study tested an hypothesis concerning patterns in species abundance in ecological communities. Why do the majority of
species occur in low abundance, with just a few making up the bulk of the biomass? We propose that many of the minor species
are analogues of the dominants in terms of the ecosystem functions they perform, but differ in terms of their capabilities
to respond to environmental stresses and disturbance. They thereby confer resilience on the community with respect to ecosystem
function. Under changing conditions, ecosystem function is maintained when dominants decline or are lost because functionally
equivalent minor species are able to substitute for them. We have tested this hypothesis with respect to ecosystem functions
relating to global change. In particular, we identified five plant functional attributes—height, biomass, specific leaf area,
longevity, and leaf litter quality—that determine carbon and water fluxes. We assigned values for these functional attributes
to each of the graminoid species in a lightly grazed site and in a heavily grazed site in an Australian rangeland. Our resilience
proposition was cast in the form of three specific hypotheses in relation to expected similarities and dissimilarities between
dominant and minor species, within and between sites. Functional similarity—or ecological distance—was determined as the euclidean
distance between species in functional attribute space. The analyses provide evidence in support of the resilience hypothesis.
Specifically, within the lightly grazed community, dominant species were functionally more dissimilar to one another, and
functionally similar species more widely separated in abundance rank, than would be expected on the basis of average ecological
distances in the community. Between communities, depending on the test used, two of three, or three of four minor species
in the lightly grazed community that were predicted to increase in the heavily grazed community did in fact do so. Although
there has been emphasis on the importance of functional diversity in supporting the flow of ecosystem goods and services,
the evidence from this study indicates that functional similarity (between dominant and minor species, and among minor species)
may be equally important in ensuring persistence (resilience) of ecosystem function under changing environmental conditions.
Foresters are showing increasing interest in the advantages to timber production of certain mixtures of plantings. We have studied decomposition and nutrient release in litters from tree mixtures compared with pure stands. Comparisons have been made of nutrient dynamics in pure and two-species mixtures of oak (Quercus petraea), alder (Alnus glutinosa) and Norway spruce (Picea abies), planted in a replicated design in 1955.Nutrient availability and tree growth were enhanced in the spruce/pine and depressed in the spruce/alder and spruce/oak mixtures compared with single-species stands. Increased mobilization rates in the spruce/pine and decreased rates in the spruce/alder and spruce/oak were correlated with increased and decreased metabolic activity, respectively, and changes in the decomposer community of the forest floor.It is suggested that a species of litter with a relatively high nutrient concentration, when added to a low-quality litter may enhance decomposition and nutrient release of the latter. It is concluded that part of the explanation for modified growth of trees in mixtures compared with pure stands is to be found in the interactions between invertebrates and microorganisms in the litter, which result in changes in nutrient dynamics.
Leguminous plant materials used as mulches, green manures and cover crops are generally assumed to provide a readily-available source of N to crops. However, little is known about the chemical composition and N release patterns of the variety of legumes being used in tropical agroecosystems. N release patterns from the leaflets of 10 troplcal legumes and rice straw were determined in a laboratory experiment. Ground leaf material was allowed to decompose in an acid soil (pH 4.5) for 8 weeks and the soil was analyzed periodically for extractable NH4+-N and NO3∼, -N. N release in the soil plus plant material were compared to that of the soil without plant material added and related to the N, lignin and polyphenolic concentrations of the leaflets. Three patterns of net N mineralization emerged during the 8-weeks. One pattern exhibited by the control soil, rice straw and leaves of two of the leguminous plants was a low, positive net mineralization. Another pattern showed much higher rates of mineralization than the control soil and the third pattern showed initial net immobilization followed by low but positive net mineralization rates. The amount of N mineralized during the 8 weeks as compared to the control soil ranged from +46 to −20% of the N added in plant material. Net mineralization was not correlated to % N or % lignin in the leaf material but was found to be negatively correlated to the polyphenolic concentration, r = −0.63, or the polyphenolic-to-N ratio, r = −0.75. Mineralization in excess of the control soil was found only for materials with a polyphenolic-to-N ratio < 0.5. Mechanisms to explain the low mineralization by materials high in polyphenolics include the formation of stable polymers between polyphenolics and amino groups, and nitrosation, a chemical reaction of nitrite (NO2) with polyphenolics. Our results show that leguminous plant material with a high polyphenolic content or polyphenolic-to-N ratio may not be a readily-available source of N.
Three general methods for obtaining measures of diversity within a population and dissimilarity between populations are discussed. One is based on an intrinsic notion of dissimilarity between individuals and others make use of the concepts of entropy and discrimination. The use of a diversity measure in apportionment of diversity between and within populations is discussed.
Numerous investigators have suggested that herbivores almost always increase rates of nutrient and energy flow through terrestrial ecosystems by returning to the soil fecal material and urine with faster turnover rate than shed plant litter. These previous theories and models always treat the producer compartment as a homogenous pool. Essentially, they assume that consumers feed through a pureed cream of vegetable soup. However, many field observations and experiments have shown that consumers feed selectively (i.e., in a cafeteria) and that consumer choice is made on the same chemical basis that determines decomposition rates. Plants that are preferred food sources often have higher nutrient content, higher growth rates, and faster decomposition rates. As consumption reduces dominance of these species in favor of unpreferred species with slower decomposition, rates of nutrient cycling and energy flow should therefore decline. We analyze a model in which the consumer is given a choice among producers that vary in nutrient uptake rates, rates of nutrient return to decomposers, and consumer preference, and which is parameterized for plants and consumers characteristic of boreal regions. In this model, in an open, well-mixed system with one consumer and two such producers, the nutrient/energy flow will not exceed that of a system without the consumer. If the consumer has a choice between two such producers, it must choose one plant over the other at a greater ratio than that between the two plants in uptake and decay rates. In contrast, in a closed system the consumer must be less selective to coexist with the two plants. The system behavior is determined by the level of nutrient return through the consumer and the differences between the plants in nutrient uptake rates and consumer preference. Species richness affects properties of this model system to the extent that species are functionally distinct (i.e., have different rate constants) in a multivariate space of life history traits (i.e., nutrient uptake and palatability). We suggest that the biochemical variability of plant tissues that simultaneously determines both consumer preference and decomposition rates is an essential feature of food webs that cannot be ignored. Thus, ecosystem models should, at minimum, consider more than one producer type with consumer preference.
The influence of intraspecific variation on ecosystem functioning is relatively unknown. We investigated the effects of litter phenotype on carbon and nitrogen fluxes in the litter and soil, and on microarthropod and bacterial populations over a 3-year period. Different litter phenotypes significantly affected carbon and nitrogen fluxes. Short- and long-term fluxes within single phenotype treatments were significantly, but unpredictably, different from a mixed phenotype treatment. Fluxes were associated with variation in litter chemistry which has a significant genetic component. We found no effects of phenotype identity on soil bacterial or microarthropod communities. However, persistent litter phenotype effects upon carbon and nitrogen fluxes support our previous suggestion that losses in genetic diversity may influence ecosystem processes.
Often there are significant positive interspecific relationships between leaf area per unit dry mass (SLA) and foliar phosphorus and nitrogen concentrations ([P] and [N]). Most of these studies have been conducted on moderately acidic soils, and little is known of the generality of these relations as potentially affected by soil characteristics. We investigated foliage mineral composition in relation to leaf structure in a wooded meadow on calcareous alkaline soil, in a bog on strongly acidic soil, and in a flood plain on moderately acidic soil. Foliar nutrient contents and fertilization experiments indicated that foliage physiological activity was co-limited by both P and N availabilities in the wooded meadow, by P in the bog, and by N in the flood plain. In the wooded meadow and in the bog, there were positive relationships between SLA and P concentration ([P]), and no relationship between SLA and nitrogen concentration [N]. Given that the fraction of support tissues generally increases with decreasing SLA, the requirement for mineral nutrients is lower at low SLA. Thus, these contrasting relations between mineral nutrients and SLA suggest that P was distributed in a more “optimal” manner among the leaves with varying structure than N in P-limited communities. In the flood plain, SLA was positively related to both [P] and [N], possibly manifesting a strategy to cope with N limitations by enhancing N turnover, and accordingly, greater P requirement for nucleic acid formation in N-limited soils. Total variation in foliar structural and chemical characteristics was similar in all sites, and was mainly determined by variation among the species. Part of this variability was explained by life form and plant size. [P] was higher in trees than in shrubs, and [P] and P/N ratio increased with increasing total plant height, indicating that P nutrition was improved relative to N nutrition with increasing plant size. Since the capture of less mobile soil elements such as P is dependent on extensive root systems, but not that of readily mobile and temporarily variable elements such as N, this correlation was attributed to more extensive root systems in larger plants. Our study indicates that foliar structure vs. [N] and [P] relations may be separately regulated, but also that the generality of leaf structure vs. nutrient content relations may vary depending on soil conditions.
We examined the effects of decreasing plant diversity and functional group identity on root biomass, soil bulk density, soil nitrate and ammonium concentrations, microbial basal respiration, density of predaceous and non-predaceous nematodes, earthworm biomass and density and Shannon–Wiener indices of earthworm diversity in a temperate grassland. Plant species and functional group diversity did not have significant effects on any of these measured variables. However, functional group identity of the plants did significantly affect root biomass and soil abiotic factors. In addition, root biomass, Shannon–Wiener indices of earthworm diversity and density of epigeic earthworms were significantly higher in the presence of legumes, while we found no correlation between functional group identity and other groups of soil biota. We also found several significant relationships among root biomass density, soil microbial basal respiration, nematodes and earthworms.
In this study, we developed simple, phenomenological models that enabled us to examine whether litter mixtures of differing quality increased, decreased, or had no effect on the rate of net N mineralization relative to a model that extrapolated the expected result assuming no interaction among litters of differing quality. We found that the presence of low quality litter (e.g., litter with a high lignin:N ratio) held the rate of net N mineralization to a uniformly low level until > 70% of the litter mixture was dominated by species of high litter quality. After this point, there was a rapid increase in the rate of net N mineralization. Although there was a relatively small difference in the predicted rate of net N mineralization (1 kg ha(-1) 28 d(-1)) between the two models tone assuming an interaction among litter types and the second, no interaction), applied over larger spatial and temporal scales, this relatively subtle difference could lead to considerably different estimated rates of N supply to saplings and canopy trees over the course of forest succession. (C) 1998 Elsevier Science B.V.
This study tested a hypothesis concerning patterns in species abundance in ecological communities. Why do the majority of species occur in low abundance, with just a few making up the bulk of the biomass? We propose that many of the minor species are analogues of the dominants in terms of the ecosystem functions they perform, but differ in terms of their capabilities to respond to environmental stresses and disturbance. They thereby confer resilience on the community with respect to ecosystem function. Under changing conditions, ecosystem function is maintained when dominants decline or are lost because functionally equivalent minor species are able to substitute for them. We have tested this hypothesis with respect to ecosystem functions relating to global change. In particular, we identified five plant functional attributes - height, biomass, specific leaf area, longevity, and leaf litter quality - that determine carbon and water fluxes. We assigned values for these functional attributes to each of the graminoid species in a lightly grazed site and in a heavily grazed site in an Australian rangeland. Our resilience proposition was cast in the form of three specific hypotheses in relation to expected similarities and dissimilarities between dominant and minor species, within and between sites. Functional similarity - or ecological distance - was determined as the Euclidean distance between species in functional attribute space. The analyses provide evidence in support of the resilience hypothesis. Specifically, within the lightly grazed community, dominant species were functionally more dissimilar to one another, and functionally similar species more widely separated in abundance rank, than would be expected on the basis of average ecological distances in the community. Between communities, depending on the test used, two of three, or three of four minor species in the lightly grazed communities that were predicted to increase in the heavily grazed community did in fact do so.. Although there has been emphasis on the importance of functional diversity in supporting the flow of ecosystem goods and services, the evidence from this study indicates that functional similarity (between dominant and minor species) may be equally important in ensuring persistence (resilience) of ecosystem function under changing environmental conditions.
This paper uses theory and experiments to explore the effects of diversity on stability, productivity, and susceptibility to invasion. A model of resource competition predicts that increases in diversity cause community stability to increase, but population stability to decrease.. These opposite effects are, to a great extent, explained by how temporal variances in species abundances scale with mean abundance, and by the differential impact of this scaling on population vs. community stability. Community stability also depends on a negative covariance effect (competitive compensation) and on overyielding (ecosystem productivity increasing with diversity). A longterm study in Minnesota grasslands supports these predictions.
Models of competition predict, and field experiments confirm, that greater plant diversity leads to greater primary productivity. This diversity-stability relationship results both from the greater chance that a more productive species would be present at higher diversity (the sampling effect) and from the better "coverage" of habitat heterogeneity caused by a broader range of species traits in amore diverse community(the niche differentiation effect). Both effects cause more complete utilisation of limiting resources at higher diversity, which increases resource retention, further increasing productivity. Finally, lower levels of available limiting resources at higher diversity are predicted to decrease the susceptibility of an ecosystem to invasion, supporting the diversity-stability hypothesis. This mechanism provides rules for community assembly and invasion resistance.
In total, biodiversity should be added to species composition, disturbance, nutrient supply, and climate as a major controller of population and ecosystem dynamics and structure. By their increasingly great directional impacts on all of these controllers, humans are likely to cause major longterm changes in the functioning of ecosystems worldwide. A better understanding of these ecosystem changes is needed if ecologists are to provide society with the knowledge essential for wise management of the Earth and its biological resources.
Experimental investigations of the relationship between biodiversity and ecosystem functioning (BEF) directly manipulate diversity then monitor ecosystem response to the manipulation. While these studies have generally confirmed the importance of biodiversity to the functioning of ecosystems, their broader significance has been difficult to interpret. The main reasons for this difficulty concern the small scales of the experiment, a bias towards plants and grasslands, and most importantly a general lack of clarity in terms of what attributes of functional diversity (FD) were actually manipulated. We review how functional traits, functional groups, and the relationship between functional and taxonomic
diversity have been used in current BEF research. Several points emerged from our review.
First, it is critical to distinguish between response and effect functional traits when quantifying or manipulating FD. Second, although it is widely done, using trophic position as a functional group designator does not fit the effect-response trait division needed in BEF research. Third, determining a general relationship between taxonomic and FD is neither necessary nor desirable in BEF research. Fourth, fundamental principles in community and biogeographical ecology that have been largely ignored in BEF research could serve to dramatically improve the scope and predictive capabilities of BEF research. We suggest that distinguishing between functional response traits and functional effect traits both in combinatorial manipulations of biodiversity and in descriptive studies of BEF could markedly improve the power of such studies. We construct a possible framework for predictive, broad-scale BEF research that requires integrating functional, community, biogeographical, and ecosystem ecology with taxonomy.