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Warming reduces the cover, richness and evenness of lichen-dominated biocrusts but promotes moss growth: Insights from an 8 yr experiment
New Phytologist
Abstract
Despite the important role that biocrust communities play in maintaining ecosystem structure and functioning in drylands world-wide, few studies have evaluated how climate change will affect them. �
Using data from an 8-yr-old manipulative field experiment located in central Spain, we evaluated how warming, rainfall exclusion and their combination affected the dynamics of biocrust communities in areas that initially had low (<20%, LIBC plots) and high (>50%, HIBC plots) biocrust cover. �
Warming reduced the richness (35�6%), diversity (25�8%) and cover (82�5%) of biocrusts in HIBC plots. The presence and abundance of mosses increased with warming through time in these plots, although their growth rate was much lower than the rate of lichen death, resulting in a net loss of biocrust cover. On average, warming caused a decrease in the abundance (64�7%) and presence (38�24%) of species in the HIBC plots. Over time, lichens and mosses colonized the LIBC plots, but this process was hampered by warming in the case of lichens. �
The observed reductions in the cover and diversity of lichen-dominated biocrusts with warming will lessen the capacity of drylands such as that studied here to sequester atmospheric CO2 and to provide other key ecosystem services associated to these communities.
... In semiarid regions of Spain, rising temperatures have reduced the coverages of lichens and mosses [ 9 ]. In addition, a study found that warming reduced the cover of nitrogen-fixing lichens on the Colorado Plateau [ 10 ]. At the same time, warming will promote soil carbon emissions from biocrust soil, which negatively impacts carbon storage [ 11 ]. ...
... However, researchers have found that warming can promote the growth of cyanobacteria [ 25 ] and mosses [ 10 ], which may be due to differences in the adaptability of biocrusts to temperature conditions in different regions. Warming reduces the diversity of biocrusts in arid areas and alters community structure and function, which also leads to a decrease in biocrust adaptability to temperature [ 27 ]. ...
... Long-term climate conditions have created a unique tolerance range for temperature and moisture in local biocrusts. When the temperature exceeds the appropriate temperature range, it will negatively impact biocrust survival [ 10 ]. Furthermore, mosses typically revives during seasons with advantageous air humidity and soil moisture [ 28 ]. ...
Biological soil crusts (biocrusts), as an important component of dryland ecosystems, play a crucial role in regulating ecosystem stability and sustainability. However, how their distribution will respond to future climate change is still not fully discussed. We took the Loess Plateau (LP) region of China as the research area and used the maximum entropy (MaxEnt) model to simulate the potential distributions (PDs) of biocrusts from 1970 to 2100. This was achieved by coupling bioclimatic variables, soil factors, and terrain factor data under 3 shared socioeconomic pathways (SSP126, SSP245, and SSP585). The PDs of 3 types of biocrusts (cyanobacteria, mosses, and lichens) were simulated and analyzed. The results showed that (a) the minimum temperature in the coldest month, rainfall in the wettest month, and rainfall in the warmest season are the most important bioclimatic variables affecting the PDs of cyanobacteria, mosses, and lichens, respectively. Among the soil factors, soil nitrogen content had the greatest influence on the PD of biocrusts. (b) The PDs of cyanobacteria, mosses, and lichens will be minimized by 2100 under the SSP585 scenario, with suitable distribution areas decreasing by 68.7%, 75.8%, and 36.5%, respectively, compared to those in historical periods. (c) The PDs of biocrusts on the LP will shift to higher-altitude regions with low temperatures and less precipitation in future climate change. This study can help us understand the response mechanism of biocrusts to future climate change and provide a basis for the restoration of biocrusts in other vulnerable ecological regions worldwide.
... In habitats such as drylands, their survival relies on a delicate equilibrium between the tolerance to high temperatures and radiation and the need of occasionally getting wet to prevent severe structural harm due to prolonged desiccation Wu et al. 2013). Studies conducted over the last decade have shown that warming and altered rainfall regimes have a negative effect on the cover, diversity and photosynthetic capacity of biocrust communities dominated by mosses and lichens (Ferrenberg et al. 2015;Guan et al. 2019;Ladrón de Guevara et al. 2018;Ladrón de Guevara et al. 2014;Maestre et al. 2015;Maestre et al. 2013;Maphangwa et al. 2012). However, there are still important gaps in our understanding of the mechanisms underlying the negative effects of warming on the physiological performance (e.g., reduction of the length of the metabolic activity period and derived effects) and growth of biocrust constituents (Reed et al. 2016). ...
... Increases in temperature and reductions in relative moisture promoted by our warming treatment reduced the length of active period in Psora during the day, negatively impacting on the status of PSII and suggesting a stress response to this treatment. Our results point to water availability as an important regulator of the effect of warming over the functional performance of Psora, and provide a mechanistic physiological explanation for observed declines in the cover of biocrust-forming lichens with warming in field experiments (Ferrenberg et al. 2015;Ladrón de Guevara et al. 2018). Our findings also highlight the value of continuous physiological measurements, and of % of activity in particular, as a tool to monitor the response of biocrust constituents like lichens to ongoing climate change. ...
... This pattern confines metabolic activity in spring to cooler situations with lower light availability, thus reducing optimal situations to achieve optimal net photosynthetic values (Fig. 3). Ladrón de Guevara et al. (2018) showed that the limitation of soil surface moisture in artificially warmed biocrusts including Psora could underlie the reductions in cover, richness and evenness observed in the field. Colesie et al. (2016) demonstrated that Psora could exploit soil water as an extra metabolic activity driver through versatile rhizines. ...
Purpose
Biocrust communities, which are important regulators of multiple ecosystem functions in drylands, are highly sensitive to climate change. There is growing evidence of the negative impacts of warming on the performance of biocrust constituents like lichens in the field. Here, we aim to understand the physiological basis behind this pattern.
Methods
Using a unique manipulative climate change experiment, we monitored every 30 minutes and for 9 months the chlorophyll a fluorescence and microclimatic conditions (lichen surface temperature, relative moisture and photosynthetically active radiation) of Psora decipiens , a key biocrust constituent in drylands worldwide. This long-term monitoring resulted in 11,847 records at the thallus-level, which allowed us to evaluate the impacts of ~2.3 °C simulated warming treatment on the physiology of Psora at an unprecedented level of detail.
Results
Simulated warming and the associated decrease in relative moisture promoted by this treatment negatively impacted the physiology of Psora , especially during the diurnal period of the spring, when conditions are warmer and drier. These impacts were driven by a mechanism based on the reduction of the length of the periods allowing net photosynthesis, and by declines in Yield and Fv/Fm under simulated warming.
Conclusion
Our study reveals the physiological basis explaining observed negative impacts of ongoing global warming on biocrust-forming lichens in the field. The functional response observed could limit the growth and cover of biocrust-forming lichens in drylands in the long-term, negatively impacting in key soil attributes such as biogeochemical cycles, water balance, biological activity and ability of controlling erosion.
... Furthermore, the microtopography created by biocrust constituents like lichens could facilitate the capture of silt and clay particles from dust (Fick et al., 2020), increasing soil water and nutrient contents (Delgado-Baquerizo et al., 2015;Eldridge et al., 2020), promoting higher rates of microbial activity (Delgado-Baquerizo et al., 2015) and avoiding P losses via lixiviation (Belnap, 2011;Belnap et al., 2004). Different experiments have shown how warming and altered rainfall regimes such as those forecasted under climate change can dramatically decline the cover and abundance of lichen-and moss-dominated biocrusts (Ferrenberg et al., 2015;Ladrón de Guevara et al., 2018;Maestre et al., 2015), with cascading effects on the C and N cycles driven by this decline (Delgado-Baquerizo et al., 2014;Liu et al., 2016Liu et al., , 2017Maestre et al., 2013;Reed et al., 2012). However, there is no experimental evidence about whether dryland biocrusts can modulate all P soil fractions, which will determine its availability for plants at short, medium and long terms, in the topsoil under climate change. ...
... Previous experiments conducted in drylands have reported that simulated warming has been found to reduce microbial diversity and biomass (DeAngelis et al., 2015;Delgado-Baquerizo et al., 2014;Maestre et al., 2015), the cover of biocrust-forming lichens (Ladrón de Guevara et al., 2018) and higher UV degradation of plant and lichen litter (Almagro et al., 2015;Belnap, 2011;Berdugo et al., 2021;Castenholz and Garcia-Pichel, 2012). The death of biocrust-forming lichens (including the release of immobilized P by the microbes) and ...
... the subsequent decomposition of their tissues mediated by warming (Berdugo et al., 2021;Ladrón de Guevara et al., 2018) may explain the increase in labile P and organic P in the topsoil in our experiment. ...
Ongoing global warming and alterations in rainfall patterns driven by climate change are known to have large impacts on biogeochemical cycles, particularly on drylands. In addition, the global increase in atmospheric nitrogen (N) deposition can destabilize primary productivity in terrestrial ecosystems, and phosphorus (P) may become the most limiting nutrient in many terrestrial ecosystems. However, the impacts of climate change on soil P pools in drylands remain poorly understood. Furthermore, it is unknown whether biocrusts, a major biotic component of drylands worldwide, modulate such impacts.
Here we used two long‐term (8–10 years) experiments conducted in Central (Aranjuez) and SE (Sorbas) Spain to test how a ~2.5°C warming, a ~30% rainfall reduction and biocrust cover affected topsoil (0–1 cm) P pools (non‐occluded P, organic P, calcium bound P, occluded P and total P).
Warming significantly increased most P pools—except occluded P—in Aranjuez, whereas only augmented non‐occluded P in Sorbas. The rainfall reduction treatment had no effect on the soil P pools at any experimental site. Biocrusts increased most soil P pools and conferred resistance to simulated warming for major P pools at both sites, and to rainfall reduction for non‐occluded and occluded P in Aranjuez.
Synthesis. Our findings provide novel insights on the responses of soil P pools to warming and rainfall reduction, and highlight the importance of biocrusts as modulators of these responses in dryland ecosystems. Our results suggest that the observed negative impacts of warming on dryland biocrust communities will decrease their capacity to buffer changes in topsoil P driven by climate change.
... In contrast to the studies from the Colorado Plateau, the cover of mosses increased with warming in these experiments, but this did not suffice to compensate the drastic reduction in lichen cover observed (Escolar et al., 2012;Ladrón de Guevara et al., 2018). On a physiological level, warming experiments have revealed that only some lichen species are able to adapt to warmer temperatures by increasing net photosynthesis, and thus balancing higher respiratory losses, but others are not (Colesie et al., 2018). ...
... First, they are restricted to relatively small research areas and short time-scales: all experiments conducted to date have been running for 15 years or less (Dacal et al., 2020;Ferrenberg et al., 2015). Second, manipulative climate change treatments potentially introduce unintended side effects that can influence the results (Carlyle et al., 2011) and different manipulation methods can hamper the comparison between studies (Bokhorst et al., 2013;Klein et al., 2005;Ladrón de Guevara et al., 2018). Also, with experiments alone it is difficult to understand climate change impacts on individual physiological processes, and thus gaining a mechanistic understanding of how these impacts translate to the observed changes in growth, cover and composition at the community level. ...
... Additionally, studies have shown a similar physiological responses of biocrusts dominated by this and other species to micro-and macro-environmental variables (Raggio et al., , 2017, suggesting that results obtained for D. diacapsis might to some degree be generalisable. Empirical studies also show that this species is particularly affected by increased temperatures (Escolar et al., 2012;Ladrón de Guevara et al., 2018). ...
Manipulative experiments typically show a decrease in dryland biocrust cover and altered species composition under climate change. Biocrust‐forming lichens, such as the globally distributed Diploschistes diacapsis, are particularly affected and show a decrease in cover with simulated climate change. However, the underlying mechanisms are not fully understood, and long‐term interacting effects of different drivers are largely unknown due to the short‐term nature of the experimental studies conducted so far.
We addressed this gap and successfully parameterised a process‐based model for D. diacapsis to quantify how changing atmospheric CO2, temperature, rainfall amount and relative humidity affect its photosynthetic activity and cover. We also mimicked a long‐term manipulative climate change experiment to understand the mechanisms underlying observed patterns in the field.
The model reproduced observed experimental findings: warming reduced lichen cover, whereas less rainfall had no effect on lichen performance. This warming effect was caused by the associated decrease in relative humidity and non‐rainfall water inputs, which are major water sources for biocrust‐forming lichens. Warming alone, however, increased cover because higher temperatures promoted photosynthesis during early morning hours with high lichen activity. When combined, climate variables showed non‐additive effects on lichen cover, and effects of increased CO2 levelled off with decreasing levels of relative humidity.
Synthesis. Our results show that a decrease in relative humidity, rather than an increase in temperature, may be the key factor for the survival of the lichen D. diacapsis under climate change and that effects of increased CO2 levels might be offset by a reduction in non‐rainfall water inputs in the future. Because of a global trend towards warmer and drier air and the widespread global distribution of D. diacapsis, this will affect lichen‐dominated dryland biocrust communities and their role in regulating ecosystem functions worldwide.
... In temperate systems, soil-dwelling lichens and mosses are often most abundant in drier regions due to reduced competition from vascular plants (Corbin & Thiet, 2020;Zhang et al., 2016), and experimental evidence predicts largely unfavourable outcomes at the arid limits of their ranges (Ferrenberg et al., 2015;Maestre et al., 2015;Reed et al., 2012). Yet, some studies from the Iberian Peninsula have reported increased abundances of biocrust mosses under simulated warming in the arid zone (Escolar et al., 2012;Ladrόn de Guevara et al., 2018). While there are many interacting factors involved, such as trampling disturbance and wildfire (Ferrenberg et al., 2015;Joly et al., 2009), the mixed results from community-level experiments highlight the need to explore the idiosyncratic responses of lichens and mosses at the species level. ...
... Our first aim was to assess the relative importance of various climate and land use variables in controlling the distributions of selected lichens and mosses. Of all climate variables, temperature has often been shown to be the most important control on the distributions of lichens and mosses (Finger-Higgins et al., 2022;Ladrόn de Guevara et al., 2018). Notably, temperature in the wettest quarter is likely to be critical, since lichens and mosses are highly susceptible to thermal damage when hydrated (Nörr, 1974;Oukarroum et al., 2012). ...
Aim
Lichens and mosses play important functional roles in all terrestrial ecosystems, particularly in tundra and drylands. As with all taxa, to maintain their current niche in a changing climate, lichens and mosses will have to migrate. However, there are no published estimates of future habitat suitability or necessary rates of migration for members of these groups at the global scale.
Taxon
Lichens and mosses.
Location
Global.
Methods
Using global occurrence data, we conducted ensemble distribution models in the ‘biomod2’ R package, parameterised with a range of climatic, land use and soil variables, to estimate current and future (2100) habitat suitability in 16 abundant species of lichen and moss.
Results
Without considering dispersal limitation, suitable area was forecast to expand for eight species and decline for four species. For species with predominantly boreo‐arctic distributions, suitable area typically declined at the temperate range edge and expanded across the High Arctic. Future suitable area available to dryland‐adapted species generally declined overall, likely relating to the desiccation‐tolerant physiology of lichens and mosses. The average migration rates required for species to disperse into new suitable habitat ranged from 1.7 ( Placidium squamulosum ) to 9.0 km year ⁻¹ ( Syntrichia ruralis ), although most species will need to migrate >16 km year ⁻¹ to completely fill their potential future suitable habitat.
Main Conclusions
For mosses and lichens, as with all species, migration will be an important part of the adjustment to a warmer climate, but realisation of these potential migrations will require both rare dispersal events and habitat that is suitable in non‐climatic dimensions. Current evidence on dispersal in these groups suggests that these geographical shifts may be unlikely to be realised without intervention, especially in landscapes that are highly modified by humans.
... Multiple studies suggest negative impacts of warmer, drier air on the growth of NVP (e.g. Nascimbene et al., 2016;Ladr on de Guevara et al., 2018;Norby et al., 2019;Finger-Higgens et al., 2022). Moreover, indirect effects, such as increased competition with vascular plants, may further reduce NVP cover, especially in the Arctic tundra and in high-elevation ecosystems (Cornelissen et al., 2001). ...
... Key ecosystem functions of NVP on open ground vary between ecosystem types, leading to differential impacts of climate change. In drylands, warming experiments suggest negative effects on cover and diversity of biocrusts, likely due to reduced active time resulting from drier and warmer air and also higher respiration (Maestre et al., 2013;Ladr on de Guevara et al., 2018;Baldauf et al., 2021), which, however, may depend on the type of biocrust (Tucker et al., 2019;Li et al., 2021). The negative effects of warming may be exacerbated by a shift in climate variability, such as a higher number of small rainfall events, which may cause high carbon losses through maintenance respiration (Reed et al., 2012;Phillips et al., 2022). ...
Nonvascular photoautotrophs (NVP), including bryophytes, lichens, terrestrial algae, and cyanobacteria, are increasingly recognized as being essential to ecosystem functioning in many regions of the world. Current research suggests that climate change may pose a substantial threat to NVP, but the extent to which this will affect the associated ecosystem functions and services is highly uncertain. Here, we propose a research agenda to address this urgent question, focusing on physiological and ecological processes that link NVP to ecosystem functions while also taking into account the substantial taxonomic diversity across multiple ecosystem types. Accordingly, we developed a new categorization scheme, based on microclimatic gradients, which simplifies the high physiological and morphological diversity of NVP and world‐wide distribution with respect to several broad habitat types. We found that habitat‐specific ecosystem functions of NVP will likely be substantially affected by climate change, and more quantitative process understanding is required on: (1) potential for acclimation; (2) response to elevated CO2; (3) role of the microbiome; and (4) feedback to (micro)climate. We suggest an integrative approach of innovative, multimethod laboratory and field experiments and ecophysiological modelling, for which sustained scientific collaboration on NVP research will be essential.
... suggest that biocrusts are also sensitive to variations in climate and exhibit declines in late-successional community organisms (lichens and mosses) with increases in temperature or altered precipitation patterns (7,(20)(21)(22)(23). Warming experiments in the drylands of Spain found that increasing temperatures can reduce lichen species cover and richness (20)(21)(22), while moss species have shown sensitivity to altered precipitation patterns on the Colorado Plateau of North America (7,9,23). ...
... suggest that biocrusts are also sensitive to variations in climate and exhibit declines in late-successional community organisms (lichens and mosses) with increases in temperature or altered precipitation patterns (7,(20)(21)(22)(23). Warming experiments in the drylands of Spain found that increasing temperatures can reduce lichen species cover and richness (20)(21)(22), while moss species have shown sensitivity to altered precipitation patterns on the Colorado Plateau of North America (7,9,23). Additionally, climate manipulations show similar community compositional shifts as physical disturbance (7,9), as do global synthesis and modeling projects (14), thereby calling into question biocrust state stability in a warming world. ...
Significance
Across many global drylands, biocrusts form a protective barrier on the soil surface and fill many critical roles in these harsh yet fragile environments. Previous short-term research suggests that climate change and invasive plant introduction can damage and alter biocrust communities, yet few long-term observations exist. Using a globally unique long-term record of continuous biocrust surveys from a rare never-grazed, protected grassland on the US Colorado Plateau, we found lichen species diversity and cover to be negatively correlated with increasing summer air temperatures, while moss species showed more sensitivity to variation in precipitation and invasive grass cover. These results suggest that dryland systems may be at a critical tipping point where ongoing warming could result in biological soil crust degradation.
... For example, altered precipitation frequency caused rapid mortality of biocrust mosses along with a decrease in cyanobacterial abundance and shift in composition, while warming temperatures also caused substantial mortality of mosses and lichens in a long-term climate change experiment in the Colorado Plateau ecosystem, USA (Ferrenberg et al., 2015;Reed et al., 2012). Warming also led to reduced cover and diversity of biocrusts in a long-term experiment in Mediterranean-semiarid central Spain (Guevara et al., 2018). Despite the potential for global change pressures to alter biocrust community states, and for these changes to subsequently alter various ecological processes, the direct and indirect influences of biocrusts on biogeochemical pools and processes remains too poorly quantified to support forecasting of impacts to ecosystem functioning . ...
... At the same time, positive correlations among biocrusts and overall levels of biotic activity and concentrations of soil C, N, and P have been found across an array of drylands globally (Eldridge et al., 2020a). While our community types and biogeochemical results tend to align with those from experiments where warming or watering treatments have driven a reduction in lichens and mosses, and a concomitant increase in the proportion of the ground surface covered by cyanobacteria (i.e., Ferrenberg et al., 2015;Guevara et al., 2018;Reed et al., 2012), the potential for different drivers to lead to similar biogeochemical outcomes cannot be dismissed. For example, changes in biogeochemical pools and processes along natural gradients versus manipulative experiments not only result from changes in the processes supported by members of the biocrust communities (Housman et al., 2006;Maestre et al., 2013;Torres-Cruz et al., 2018;Tucker et al., 2019;Zhou et al., 2020), but also from changes in the heterotrophic microbes within biocrusts and mineral soils Ochoa-Hueso et al., 2018). ...
Biocrusts influence soil biogeochemistry by fixing carbon (C) and nitrogen (N) and through leachate inputs to soils. Functional rates can vary among biocrust community states and in response to edaphic properties, heterotrophic microbial activity, and global change. Using soils and biocrusts from the Colorado Plateau, Utah, USA, we aimed to quantify the influence of early-successional (ES) and late-successional (LS) biocrust community states on soil biogeochemistry. In a field setting, we found soil was less “fertile” under ES than LS biocrust, but ES biocrust had a relative influence 1.3 times greater than LS biocrust on soil fertility. Leachate collected from LS biocrust had, on average, 6 times more organic C and 1.7 times more dissolved N than ES biocrust, but concentrations of phosphorus (P) and inorganic N did not differ among the two biocrust types. To disentangle influences of biocrusts and soil properties on biogeochemical pools, we constructed mesocosms from homogenized soil and left the surface bare or covered with ES or LS biocrust, before assignment to ambient or warmed (+5 °C) temperature treatments for 3 months. Multivariate biogeochemical properties differed among cover types, yet all exhibited losses of P, N, and organic C and nearly half of the biogeochemical variables considered did not differ among cover types. Mesocosms with LS biocrust retained more dissolved N, supported 8 additional, significant correlations among biogeochemical pools of the biocrust and mineral soil layer on average, and lost fewer of these correlations under warming. Overall, while soils under LS biocrusts were more fertile (i.e., had higher nutrient concentrations) than under ES, we did not find evidence implicating leachate as the primary driver of this difference. Biocrust influences on soil fertility were greater when mineral soil nutrients were in lower concentrations, highlighting the value of even incipient biocrusts for dryland functioning.
... The contrasting results between our study and previous studies for both biocrust-forming lichens and mosses are likely attributed to differences in the methods, experimental designs, experimental periods, and climatic regimes of the study sites (Lange, 2001;Belnap et al., 2006;Escolar et al., 2012;Reed et al., 2012;Maestre et al., 2013;Ferrenberg et al., 2015;Maestre et al., 2015;Darrouzet-Nardi et al., 2018;Ladrón de Guevara et al., 2018;Lafuente et al., 2018). In particular, previous studies mainly simulated higher warming (2-6 • C) coupled with additional rainfall Tucker et al., 2019) or reduced rainfall using a rain shade during short (≤5 years) and medium (≤8 years) periods (Ladrón de Guevara et al., 2014;Ladrón de Guevara et al., 2018;Maestre et al., 2013). ...
... The contrasting results between our study and previous studies for both biocrust-forming lichens and mosses are likely attributed to differences in the methods, experimental designs, experimental periods, and climatic regimes of the study sites (Lange, 2001;Belnap et al., 2006;Escolar et al., 2012;Reed et al., 2012;Maestre et al., 2013;Ferrenberg et al., 2015;Maestre et al., 2015;Darrouzet-Nardi et al., 2018;Ladrón de Guevara et al., 2018;Lafuente et al., 2018). In particular, previous studies mainly simulated higher warming (2-6 • C) coupled with additional rainfall Tucker et al., 2019) or reduced rainfall using a rain shade during short (≤5 years) and medium (≤8 years) periods (Ladrón de Guevara et al., 2014;Ladrón de Guevara et al., 2018;Maestre et al., 2013). However, our study shows how biocrust components are affected by long-term small increases in warming associated with small reductions in rainfall. ...
Global warming coupled with increased drought is predicted to have a significant negative impact on desert ecosystems. In arid desert regions, a large proportion of the ground surface is covered by specialized organisms such as mosses and lichens that form biocrusts, which play a vital role in ecosystems. However, the long-term effects of warming and drought on these key biotic components of desert ecosystems remain poorly understood. Using a manipulative experiment conducted for 12 years in the Tengger Desert, northwestern China, we evaluated how both mosses and lichens in biocrust communities responded to 0.5°C and 1.5°C increases in temperature coupled with 5% and 8% reductions in total annual precipitation, respectively, using two groups of open-top chambers to approximate climate change conditions that are predicted to occur in this study region. Furthermore, surface soil carbon uptake by the biocrusts was also evaluated. Twelve years of warming coupled with increased drought resulted in a significant decrease in the cover and biomass of mosses but did not change the cover or biomass of lichens. These changes in the mosses were positively correlated with the duration and intensity of the treatments. Warming coupled with reduced precipitation significantly reduced the carbon uptake of the moss-dominated biocrusts by reducing the availability of moisture content. However, lichen carbon uptake was insensitive to the warming and reduced precipitation treatments. The reduction in cover and biomass of moss-dominated biocrusts might be attributed to large amounts of carbon loss, which further alters biocrust multifunctionality in desert ecosystems. In addition, our findings suggest that coupled warming and drought conditions could increase the dominance of lichens in biocrust communities to partly maintain the multifunctionality of biocrusts in this desert ecosystem.
... Previous research indicates that the physiological performance and growth of biocrust constituents will be negatively affected by ongoing climate change in drylands (Escolar et al., 2012;Maphangwa et al., 2012;Reed et al., 2012;Ferrenberg et al., 2015). However, this research has mainly considered biocrust communities as a whole, that is, without exploring specific responses of coexisting species within the same phylum/class (but see Maphangwa et al., 2012;Ladrón de Guevara et al., 2018). Specifically, how climate change will affect the tissue composition of biocrust constituents and associated soil properties in drylands has barely been studied, despite the potential consequences for ecosystem processes such as nutrient cycling. ...
... These species show marked differences in thallus morphology, colour and chemistry (Supporting Information Fig. S1), and exert species-specific effects on soil chemistry and microbial communities (Concostrina-Zubiri et al., 2013;Delgado-Baquerizo et al., 2015). Their performance and abundance in the field are also affected by simulated warming (Escolar et al., 2012;Ladrón de Guevara et al., 2018). ...
Biocrusts are key drivers of ecosystem functioning in drylands, yet our understanding of how climate change will affect the chemistry of biocrust‐forming species and their impacts on carbon (C) and nitrogen (N) cycling is still very limited.
Using a manipulative experiment conducted with common biocrust‐forming lichens with distinct morphology and chemistry (Buellia zoharyi, Diploschistes diacapsis, Psora decipiens and Squamarina lentigera), we evaluated changes in lichen total and isotopic C and N and several soil C and N variables after 50 months of simulated warming and rainfall reduction.
Climate change treatments reduced δ¹³C and the C : N ratio in B. zoharyi, and increased δ¹⁵N in S. lentigera. Lichens had species‐specific effects on soil dissolved organic N (DON), NH4+, β‐glucosidase and acid phosphatase activity regardless of climate change treatments, while these treatments changed how lichens affected several soil properties regardless of biocrust species. Changes in thallus δ¹³C, N and C : N drove species‐specific effects on dissolved organic nitrogen (DON), NH4+, β‐glucosidase and acid phosphatase activity.
Our findings indicate that warmer and drier conditions will alter the chemistry of biocrust‐forming lichens, affecting soil nutrient cycling, and emphasize their key role as modulators of climate change impacts in dryland soils.
... A study on specific biocrustforming lichens and mosses yielded similar findings (Mallen-Cooper et al. 2023). Rising air temperature and reduction of dew events can directly lead to the death of biocrusts due to carbon starvation (Grote et al. 2010;Ladrón de Guevara et al. 2018;Phillips et al. 2022), although it can also play a role on ecohydrological processes of evaporation and transpiration (Kalma et al. 2008). However, a dynamic global vegetation model -Libry considered hydrological, biogeochemical, physiological, disturbance processes performs not good enough to predict global biocrust distribution, and demands high-quality data, which are generally missing or difficult to obtain (Porada et al. 2013). ...
Aims
Biocrusts, communities dominated by mosses, lichens, cyanobacteria, algae, and fungi living on the soil surface, constitute a vital biotic component of dryland ecosystems that play critical roles in maintaining their structure and functioning. However, there are substantial knowledge gaps regarding the global distribution of biocrusts, which has primarily been estimated using statistical methods. Given that water is a key limiting factor for dryland biota, it holds significant potential as a key driver of the global distribution of biocrusts.
Methods
Here we utilized a novel global biocrust dataset comprising 2348 data points from six continents (excluding Antarctica) and adapted an existing ecohydrological model to predict biocrust cover across global drylands.
Results
We found that in the regions with sufficient data, such as the Loess Plateau in China, the ecohydrological model reached good correlation coefficients between the simulated and observed biocrust cover (average correlation coefficient of 100 simulations was 0.727, with a corresponding RMSE of 0.311). However, at a global scale the model was unable to reproduce observed biocrust cover (correlation coefficient < 0.352, RMSE > 0.331). The high variability observed in biocrust cover globally may contribute to the low performance of the model at this scale.
Conclusions
Our findings indicate that ecohydrological models show promise to map biocrust distribution at the regional scale when accompanied with region-specific detailed information about biocrusts and improved environmental data. They also provide a stepping-stone for future research to advance towards a mechanism-based prediction of global biocrust distribution.
... Similar to the effects of anthropogenic disturbances, climate change can cause well-developed biocrusts to regress to early-successional and species-poor communities, significantly compromising their capacity to fix C and N (Ferrenberg et al., 2015;Housman et al., 2006;Lange, 2001;Tucker et al., 2019). Evaporative stress and increasing aridity associated with warming temperatures have also been shown to increase moss mortality (Ladrón de Guevara et al., 2018;Maestre et al., 2013), decline the abundance and diversity of fungi and bacteria (Maestre, Delgado-Baquerizo, et al., 2015;Rodríguez et al., 2024), and reduce the cover of N-fixing lichens (Finger-Higgens et al., 2022). Moreover, a growing body of evidence shows how warming coupled with infrequent precipitation diminishes the photosynthetic capacity of biocrusts, compromising their ability to maintain net C uptake (Maestre et al., 2013;Reed et al., 2012;Tucker et al., 2020). ...
In drylands, where water scarcity limits vascular plant growth, much of the primary production occurs at the soil surface. This is where complex macro- and microbial communities, in an intricate bond with soil particles, form biological soil crusts (biocrusts). Despite their critical role in regulating C and N cycling in dryland ecosystems, there is limited understanding of the fate of biologically fixed C and N from biocrusts into the mineral soil, or how climate change will affect C and N fluxes between the atmosphere, biocrusts, and subsurface soils. To address these gaps, we subjected biocrust–soil systems to experimental warming and drought under controlled laboratory conditions, monitored CO2 fluxes, and applied dual isotopic labeling pulses (13CO2 and 15N2). This allowed detailed quantification of elemental pathways into specific organic matter (OM) pools and microbial biomass via density fractionation and phospholipid fatty acid analyses. While biocrusts modulated CO2 fluxes regardless of the temperature regime, drought severely limited their photosynthetic C uptake to the extent that the systems no longer sustained net C uptake. Furthermore, the effect of biocrusts extended into the underlying 1 cm of mineral soil, where C and N accumulated as mineral-associated OM (MAOM<63μm). This was strongly associated with increased relative dominance of fungi, suggesting that fungal hyphae facilitate the downward C and N translocation and subsequent MAOM formation. Most strikingly, however, these pathways were disrupted in systems exposed to warming, where no effects of biocrusts on the elemental composition of the underlying soil nor on MAOM were determined. This was further associated with reduced net biological N fixation under combined warming and drought, highlighting how changing climatic conditions diminish some of the most fundamental ecosystem functions of biocrusts, with detrimental repercussions for C and N cycling and the persistence of soil organic matter pools in dryland ecosystems.
... A study on specific biocrustforming lichens and mosses yielded similar findings (Mallen-Cooper et al. 2023). Rising air temperature and reduction of dew events can directly lead to the death of biocrusts due to carbon starvation (Grote et al. 2010;Ladrón de Guevara et al. 2018;Phillips et al. 2022), although it can also play a role on ecohydrological processes of evaporation and transpiration (Kalma et al. 2008). However, a dynamic global vegetation model -Libry considered hydrological, biogeochemical, physiological, disturbance processes performs not good enough to predict global biocrust distribution, and demands high-quality data, which are generally missing or difficult to obtain (Porada et al. 2013). ...
Ecosystems may exist in alternative stable states and thereby extremely differ in ecosystem structure and functions, including gross primary productivity (GPP), which is crucial for assessing an ecosystem’s ability to capture atmospheric carbon dioxide, especially under the context of climate change. This study applied alternative stable states theory to evaluate GPP in global dryland forests, and analyzed multi-year average GPP data alongside environmental factors such as the Aridity Index and mean annual precipitation. Here, we found the existence of alternative stable states of GPP along the aridity gradient. Mean GPP were 893.12 gC/m²/year and 1539.86 gC/m²/year under lower and higher branches of alternative stable states, respectively, compared to the current mean value of 1203.02 gC/m²/year. Notably, we observed striking regional disparities in GPP, with Africa and Oceania predominantly in the higher alternative stable state, while North America and Asia were in the lower alternative stable state. However, GPP along mean annual precipitation did not exhibit alternative stable states, but a significant variation during the medium range of mean annual precipitation (241-402 mm year-1). The relationships between GPP data and environmental factors were consistent across different forest types. This study sheds light on dryland forest productivity and indicates adaptive management strategies that should be used to bolster ecosystem function in the context of climate change.
... We anticipate that because additional changes in the Great Basin include increases in cool season moisture (Bradford et al. 2020), these changes may translate into expansions of the moderate R&R 2014 category, which is also where we most frequently observed mosses. Increases in the abundance of mosses has been observed following warming in experimental settings (de Guevara et al. 2018). ...
Biological soil crusts (biocrusts) can thrive under environmental conditions that are stressful for vascular plants such as high temperatures and/or extremely low moisture availability. In these settings, and in the absence of disturbance, cover of biocrusts commonly exceeds cover of vascular plants. Arid landscapes are also typically slow to recover from disturbance and prone to altered vegetation and invasion by exotic species. In the sagebrush ecosystems, cover of annual, exotic, invasive grasses are lower where cover of biocrusts and vascular plants are greater, suggesting that biocrusts play a role in helping arid sites avoid conversion to dominance by invasive grasses. The conceptual framework for assessing ecological resistance and resilience (R&R) is used across the region to estimate the risk of invasion by annual grasses and the likelihood of recovery of native plants following disturbance. However, this framework does not currently account for biocrusts. We used data collected by the Bureau of Land Management Assessment, Inventory, and Monitoring program to relate biocrusts, specifically the presence of lichens and mosses, to the R&R framework. Lichens frequently occur on warm, dry sites, classified as lower R&R. Mosses frequently occur on sites classified as moderate or moderately low R&R. Without management practices that favor biocrusts in low‐moderate R&R, these areas may be more vulnerable to transitioning from being dominated by shrubs to annual grasses. Under climate change scenarios, the area occupied by lower R&R sites is likely to increase, suggesting that the role of biocrusts in maintaining site resistance to invasion may also increase.
... Annual Mean Temperature, contributing 11.72% to the microbiome variation, regulates resource availability, primary productivity (Pierre et al., 2020) and microbial interactions (Apple et al., 2006;Knapp & Huang, 2022). The influence of these variables on lichen physiology, growth and metabolism, including their effects on metabolic rates, water availability and nutrient dynamics, aligns with already existing research (Finger-Higgens et al., 2022;Ladr on de Guevara et al., 2018;Mallen-Cooper et al., 2023;Nascimbene et al., 2016). Notably, while temperature-related variables emerge as key contributors, precipitation-related variables, such as precipitation seasonality and annual precipitation, play a comparatively minor role. ...
The Lobaria pulmonaria holobiont comprises algal, fungal, cyanobacterial and bacterial components. We investigated L. pulmonaria's bacterial microbiome in the adaptation of this ecologically sensitive lichen species to diverse climatic conditions. Our central hypothesis posited that microbiome composition and functionality aligns with subcontinental‐scale (a stretch of ~1100 km) climatic parameters related to temperature and precipitation. We also tested the impact of short‐term weather dynamics, sampling season and algal/fungal genotypes on microbiome variation. Metaproteomics provided insights into compositional and functional changes within the microbiome. Climatic variables explained 41.64% of microbiome variation, surpassing the combined influence of local weather and sampling season at 31.63%. Notably, annual mean temperature and temperature seasonality emerged as significant climatic drivers. Microbiome composition correlated with algal, not fungal genotype, suggesting similar environmental recruitment for the algal partner and microbiome. Differential abundance analyses revealed distinct protein compositions in Sub‐Atlantic Lowland and Alpine regions, indicating differential microbiome responses to contrasting environmental/climatic conditions. Proteins involved in oxidative and cellular stress were notably different. Our findings highlight microbiome plasticity in adapting to stable climates, with limited responsiveness to short‐term fluctuations, offering new insights into climate adaptation in lichen symbiosis.
... unbalanced factors related to the water cycle, including rainfall, humidity, dew condensation, will be responsible for detrimental consequences of climate change, which in turn will be reflected in changes at the level of lichen biota (Baldauf et al., 2021;Ladrón de Guevara et al., 2018). Heatwaves are a phenomenon that appeared previously and will unfortunately become more common in many parts of the world as the climate warms (Della-Marta & Beniston, 2008;Meehl & Tebaldi, 2004). ...
Being poikilohydric, lichens are inherently exposed to alternating desiccation and hydration cycles. They can exhibit extraordinary resistance to extreme temperatures in a dehydrated state but thermal thresholds for hydrated lichens are lower. The ability of the lichen Cetraria aculeata to recovery after high temperature treatment (40°C, 60°C) at different air humidity levels (relative humidity [RH]: <15%, 25%, 50%, 75%, ≅100%) was examined to find a linkage between passive dehydration of the lichen and its physiological resistance to heat stress. The response to heating was determined by measuring parameters related to photosynthesis and respiration after 2‐ and 24‐h recovery. A higher RH level resulted in a slower decline in relative water content (RWC) in hydrated thalli. In turn, the stress resistance of active thalli depended on the ambient humidity and associated RWC reduction. Elevated temperature had a negative impact on bioenergetic processes, but only an unnatural state of permanent full hydration during heat stress resulted in a lethal effect. Hydrated lichen thalli heated at 40°C and 50% relative humidity (RH) tended to be least susceptible to stress‐induced damage. Although atypical climatic conditions may lead lichens to lethal thresholds, the actual likelihood of deadly threat to lichens due to heat events per se is debatable.
... Thus, our pioneering work that was focused on cyanobacteria BSC opens the door for a new line of research into the mechanistic details of this trophic interaction across different consumers and BSC communities. This understanding is crucial since the structure of BSC communities is expected to change dramatically in response to climate change (Ladrón de Guevara et al., 2018;Reed et al., 2012), and mechanisms that currently govern dryland ecosystems are expected to become more important also in other areas of our warming and drying world (Grünzweig et al., 2022). ...
Animals assimilate macronutrients and mineral nutrients in specific quantities and ratios to maximise fitness. To achieve this, animals must ingest different foods that contain the needed nutrients or facilitate the digestion of those nutrients. We explored how these multidimensional considerations affect the desert isopods (Hemilepistus reaumuri) curious food selection, using field and laboratory experiments. Wild isopods consumed three‐fold more macronutrient‐poor biological soil crust (BSC) than plant litter. Isopods tightly regulated macronutrient and calcium intake, but not phosphorus when eating the two natural foods and when artificial calcium and phosphorus sources substituted the BSC. Despite the equivalent calcium ingestion, isopods performed better when eating BSC compared to artificial foods. Isopods that consumed BSC sterilised by gamma‐radiation ate more but grew slower than isopods that ate live BSC, implying that ingested microorganisms facilitate litter digestion. Our work highlights the need to reveal the multifaceted considerations that affect food‐selection when exploring trophic‐interactions.
... As we continue to monitor biocrust ranges in the future, new remote sensing techniques will be pivotal in enhancing the spatial and temporal resolution of surveys (Baxter et al., 2021). Manipulative experiments suggest that the contraction of the biocrust community will be a gradual collapse of lichen and bryophytes species, followed by cyanobacteria, after about 2-4°C of additional warming Ladrón de Guevara et al., 2018;Phillips et al., 2022). Another longterm experiment testing smaller temperature increases (0.5 and 1°C above ambient) found that mosses, but not lichens, declined (Li et al., 2021). ...
The ranges of many species globally have already shifted to maintain climatic equilibrium in the face of climate change.
Biocrusts—soil surface dwelling communities of lichens, bryophytes and microbes—play important functional roles in many ecosystems, particularly in drylands. Compared to better studied animal and plant taxa, dryland biocrusts have different establishment requirements and have never been assessed for historical range shifts.
Here, we revisited the sites (N = 204) of a 25‐year‐old biocrust survey across a large area (400,000 km²) of drylands in south‐eastern Australia. We used quadratic models to quantify changes in the climate niches of 15 lichen, eight moss and five liverwort taxa, as well as biocrust cover and richness.
Our models showed that the observed climatic niches of most taxa have become hotter and drier in the past quarter century, yet the responses of the vast majority of taxa are consistent with remaining in the same geographic space. A similar pattern was observed at the community level, where the peak of biocrust cover and richness now occurs in a hotter, drier environment. Notable exceptions were the liverwort Riccia lamellosa and lichens in the genera Cladonia and Xanthoparmelia, which showed signs of contraction at their arid range edges.
Unlike more mobile taxa, most biocrust species have yet to shift geographically and may already be lagging behind the pace of climate change. One explanation for the mortality lag is that long‐term climate variability in the system is extensive, which may have selected for the ability to withstand multi‐year warm periods as long as there is an eventual return to milder conditions. However, no forecasts of future climate include a return to milder conditions, suggesting there will be an eventual loss of ecosystem multifunctionality at the contracting front. Expansion lags are most likely due to delays in the mortality of competing vascular plants.
Synthesis: Our study provides a valuable contribution to the knowledge of range shifts in understudied taxa and highlights a future need to promote the expansion of biocrusts to maintain the provision of ecosystem functions and services across their range.
... Due to the importance of biocrusts in ecosystem functioning, their growth and survival have been extensively studied through different methodological approaches (e.g. Ladrón de Guevara et al., 2018;Lange et al., 2006;Porada et al., 2019). An established measure to quantify the growth of biocrusts is their long-term carbon balance (hereafter, C balance), which corresponds to the (accumulated) net carbon flux across the system boundaries, including all relevant carbon gains and losses. ...
Biocrusts are a worldwide phenomenon, contributing substantially to ecosystem functioning. Their growth and survival depend on multiple environmental factors, including climatic ones, and the relations of these factors to physiological processes. Responses of biocrusts to individual environmental factors have been examined in a large number of field and laboratory experiments. These observational data, however, have rarely been assembled into a comprehensive, consistent framework that allows quantitative exploration of the roles of multiple environmental factors and physiological properties for the performance of biocrusts, in particular across climatic regions. Here we used a data-driven mechanistic modelling framework to simulate the carbon balance of biocrusts, a key measure of their growth and survival. We thereby assessed the relative importance of physiological and environmental factors for the carbon balance at six study sites that differ in climatic conditions. Moreover, we examined the role of seasonal acclimation of physiological properties using our framework, since the effects of this process on the carbon balance of biocrusts are poorly constrained so far. We found substantial effects of air temperature, CO2 concentration, and physiological parameters that are related to respiration on biocrust carbon balance, which differ, however, in their patterns across regions. The ambient CO2 concentration is the most important factor for biocrusts from drylands, while air temperature has the strongest impact at alpine and temperate sites. Metabolic respiration cost plays a more important role than optimum temperature for gross photosynthesis at the alpine site; this is not the case, however, in drylands and temperate regions. Moreover, we estimated a small annual carbon gain of 1.5 gm-2yr-1 by lichen-dominated biocrust and 1.9 gm-2yr-1 by moss-dominated biocrust at a dryland site, while the biocrusts lost a large amount of carbon at some of the temperate sites (e.g. -92.1 for lichen-dominated and -74.7 gm-2yr-1 for moss-dominated biocrust). These strongly negative values contradict the observed survival of the organisms at the sites and may be caused by the uncertainty in environmental conditions and physiological parameters, which we assessed in a sensitivity analysis. Another potential explanation for this result may be the lack of acclimation in the modelling approach, since the carbon balance can increase substantially when testing for seasonally varying parameters in the sensitivity analysis. We conclude that the uncertainties in air temperature, CO2 concentration, respiration-related physiological parameters, and the absence of seasonal acclimation in the model for humid temperate and alpine regions may be a relevant source of error and should be taken into account in future approaches that aim at estimating the long-term biocrust carbon balance based on ecophysiological data.
... The cover was measured using the point-sampling method. A stainless steel wire mesh of 10 cm in side with a 1 × 1 cm grid (100 sampling points) was placed over the biocrusts, and the proportion of sampling points over the biological component to the total number of points was regarded as the biocrust cover (Ladron de Guevara et al., 2018). ...
Biocrusts are prevalent and participate in many soil organic carbon (C) processes in drylands. The predicted increase in aridity will expand the biocrust cover and significantly impact soil organic C dynamics. However, how biocrusts change soil organic C decomposition and what factors drive the effect in response to climate warming remains largely unknown at a continental scale.
We measured microbial respiration and its temperature sensitivity (Q10) in bare soil lacking biocrusts and two universal biocrusted soils (cyanobacterial‐ and moss‐crusted soil) from 43 sites across a precipitation gradient from 39 to 443 mm to evaluate the relative effects of biocrusts on Q10 and the driving forces in northern China's dryland.
Microbial respiration increased and Q10 decreased with increasing precipitation in bare soil, cyanobacterial‐ and moss‐crusted soil. Biocrusts positively affected microbial respiration, with a more substantial magnitude by moss crusts than cyanobacterial crusts. Biocrusts negatively impacted Q10, and the magnitudes were similar between moss and cyanobacterial crusts. Most importantly, the relative effects of biocrusts on microbial respiration and Q10 increased with decreasing precipitation.
The positive effects of biocrusts on soil organic C content and microbial biomass carbon were positively correlated with the level of increased microbial respiration. Contrastingly, the magnitude of reduced Q10 was attributed to the biocrusts' positive effects on soil organic C quality and adverse effects on the ratio of fungal to bacterial PLFAs (F:B).
Our study provides strong evidence that biocrusts decrease the temperature sensitivity of microbial respiration in northern China's dryland. This result suggests that the predicted expanding biocrust cover is crucial for maintaining the soil organic C stability by buffering the positive impacts of climate warming on soil organic C decomposition in drylands.
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... So far, studies on diversity-stability relationships have been focused almost exclusively on vascular plant communities (Valencia et al., 2020), whereas very little is known about such relationships for cryptogams (Klanderud & Totland, 2008;Ladron de Guevara et al., 2018), despite their dominance in many northern ecosystems. The main reason that cryptogams are much understudied is that they are relatively difficult to identify to species, which may have caused ecologists to focus on the vascular components or to lump the cryptogams into more general groups that obscure species-level patterns (Martin & Mallik, 2017). ...
Community stability is a fundamental factor sustaining ecosystem functioning and is affected by species richness and species evenness. The Arctic is warming more rapidly than other biomes, and cryptogam plant species (specifically lichens and bryophytes in this study) are major contributors to tundra biodiversity and productivity. However, to our knowledge, the impacts of warming on cryptogam community stability and the underlying mechanisms have not been investigated. We conducted a 13‐year summer warming experiment in mesic birch hummock tundra vegetation near Daring Lake in the continental interior of low Arctic Canada and recorded patterns of cryptogam species abundance in several different growing seasons. Warming decreased the stability of total community abundance, had no effects on species richness, but increased species evenness and species synchrony. Structural equation model analyses indicated that higher species richness was the principal factor associated with the stronger community abundance stability in the control plots and that this effect was driven primarily by a negative correlation with species synchrony. By contrast, higher species evenness was the principal factor associated with the weakened community abundance stability in the warming plots, and this effect was driven primarily by a positive correlation with species synchrony. Our study suggests that climate warming could reduce cryptogam plant community stability in low Arctic tundra and, therefore, decrease important ecosystem services, including carbon storage and food availability to caribou in northern regions.
... Ongoing climate change is causing a profound alteration in the structure and functioning of global drylands (see Maestre et al., 2016 and references therein). In particular, increases in temperature and reductions in precipitation affect biocrust abundance and diversity (Ferrenberg et al., 2015;Ladr on de Guevara et al., 2018), with important consequences to dryland C and N nutrient cycling (Concostrina-Zubiri et al., 2021;Zelikova et al., 2012). In contrast, our understanding of how ongoing climate change impacts the effects of biocrusts on soil P cycling is still very limited. ...
Drylands are important reservoirs of soil phosphorus (P) at the global scale, although large uncertainties remain regarding how climate change will affect P cycling in these ecosystems. Biocrust‐forming lichens are important regulators of abiotic and biotic processes occurring in the soil surface, including nutrient availability and redistribution, across global drylands. However, their role as modulators of climate change impacts on soil P cycling is poorly known. We conducted a manipulative microcosm experiment to evaluate how six biocrust‐forming lichens ( Buellia zoharyi , Diploschistes diacapsis , Fulgensia subbracteata , Psora decipiens , Squamarina lentigera and Toninia sedifolia ) with diverse morphology and chemistry affect soil available P concentration and the activity of acid phosphatase after 50 months of simulated ~2°C warming and 35% rainfall reduction. Lichens increased soil available inorganic and total available P, and the activity of acid phosphatase, although the magnitude of these effects was highly species‐specific. Climate change treatments increased available organic P regardless of lichen species. Our findings provide novel experimental evidence of the importance of biocrusts as modulators of P cycling in drylands and highlight the necessity to take into account the identity of biocrust constituents when evaluating their effects on soil fertility.
Highlights
Biocrust‐forming lichens effects on soil phosphorus under simulated climate change were evaluated
A microcosm experiment with warming and rainfall reduction and six lichen species was conducted
Lichens increased available inorganic and total available P, and the activity of acid phosphatase
Biocrust‐forming lichens have species‐specific effects on phosphorus cycling in dryland soils
... The coupling of carbon deficits with high temperatures and constrained moisture was plausibly used also for explaining similar results in biocrusts dominated by mosses [63]. Warming reduced the cover, richness and evenness of lichen-dominated biocrusts in drylands [64]. Therefore, the photosynthetic activities of lichens and carbon fixation are expected to be sensitive to warming in the short term [48]. ...
Climate change and atmospheric nitrogen (N) deposition on drylands are greatly threatening these especially vulnerable areas. Soil biocrust-forming lichens in drylands can provide early indicators of these disturbances and play a pivotal role, as they contribute to key ecosystem services. In this study, we explored the effects of different long-term water availability regimes simulating climate changes and their interaction with N addition on the physiological response of the soil lichen Cladonia rangiferina. Three sets of this lichen were subjected to control, reduced watering, and reduced watering and N addition (40 kg NH4NO3 ha−1 year−1) treatments for 16 months. Finally, all samples were subjected to daily hydration cycles with N-enriched water at two levels (40 and 80 kg NH4NO3 ha−1 year−1) for 23 days. We found that reduced watering significantly decreased the vitality of this lichen, whereas N addition unexpectedly helped lichens subjected to reduced watering to cope with stress produced by high temperatures. We also found that long-term exposure to N addition contributed to the acclimation to higher N availability. Overall, our data suggest that the interactions between reduced watering and increased N supply and temperature have an important potential to reduce the physiological performance of this soil lichen.
... These studies have shown that increased precipitation either maintains biocrust-vascular plant coexistence or leads to a vascular plantdominated state Kinast et al., 2014). In contrast, increasing aridity can increase biocrust dominance, owing to its higher drought resistance and the release of competition pressure with decreased vascular plant growth Ladron de Guevara et al., 2018). However, episodic drought likely maintains the abundance of vascular plants due to the persistent suppression of litterfall and standing litter on biocrusts (Berkeley et al., 2005;. ...
Dryland ecosystems exist in various vegetation landscapes with contrasting compositions of vascular plants and biocrusts (surface‐soil mats comprised of soil particles, cyanobacteria, lichens, mosses and fungi), and they are very vulnerable to ongoing global change. However, compared to vascular plants, the responses of biocrusts and their coexistence with vascular plants to global change remain elusive.
We conducted a 5‐year experiment involving multi‐level precipitation and nitrogen addition in a desert shrubland of northern China to examine these responses.
We found that shrubs, perennial herbs and annuals exhibited facilitative, competitive and insignificant effects on biocrusts respectively. Biocrusts coexisted with vascular plants below a threshold of herbaceous productivity of approximately 70 g/m² and tended to be replaced by herbs beyond this threshold, resulting from the balance between the shade tolerance of biocrusts and herb‐induced light limitation. Increased precipitation and nitrogen enrichment altered biocrust–vascular plant composition by influencing this balance and tended to shift from a biocrust‐dominated to a vascular plant‐dominated state when the threshold was crossed.
Synthesis. Our results suggest that biocrusts can coexist with dwarf shrubs and annuals, but cannot withstand perennial herbs when the herbaceous productivity threshold was exceeded. Our findings provide new insights into the threshold and mechanisms of biocrust–vascular plant coexistence, which may greatly contribute to managing dryland ecosystems for global change.
... Dado que el efecto de las biocostras en la mayoría de las propiedades y procesos del suelo aumenta con su cobertura y su estadio evolutivo, tanto la pérdida de cobertura, como la alteración de su distribución, morfología y composición, actúan de forma sinérgica y dan lugar a fuertes impactos negativos sobre: la biodiversidad del suelo (Ladrón de Guevara et al. 2018) los ciclos biogeoquímicos (Maestre et al. 2013), el ciclo del agua (Chamizo et al. 2016) la erosión hídrica y eólica (Chamizo et al. 2012), las emisiones de polvo atmosférico (Pointing y Belnap 2012) o el balance radiactivo (Rutherford et al. 2017) y sus interacciones (Fig. 2). Por lo tanto, los efectos negativos del cambio global en las biocostras suponen una amenaza para el funcionamiento y la resiliencia de las tierras secas (García-Pichel et al. 2013;Maestre et al. 2013) que puede retroalimentar los procesos de desertificación. ...
Las biocostras son comunidades de organismos autótrofos y heterótrofos que viven en la superficie del 12% de los suelos de la Tierra, donde actúan como ingenieras del ecosistema. Son muy sensibles al cambio climático y a las alteraciones ocasionadas por diferentes actividades antrópicas. En este trabajo, revisamos los impactos de ambos tipos de perturbaciones, que afectan negativamente a los ciclos biogeoquímicos, al balance de agua y al de energía, aceleran los procesos erosivos y la emisión de polvo y reducen la biodiversidad disminuyendo la capacidad de los ecosistemas para proveer servicios. Exploramos la capacidad de estas comunidades para recuperarse naturalmente, que, en general, requiere mucho tiempo el establecimiento de las comunidades de etapas sucesionales más tardías. Por ello, han surgido nuevas biotecnologías para acelerar su restauración, basadas en la inoculación de organismos formadores de biocostra. Se revisan los principales resultados de dos grupos de estrategias atendiendo al origen de los propágulos de biocostras: a) la translocación de fragmentos de biocostras de un área donante en favor de una degradada. Se recomienda para alteraciones planificadas en las que se use la biocostra existente antes de la alteración; b) cultivo a gran escala de organismos formadores de biocostra (cianobacterias, líquenes, musgos o la comunidad completa) en laboratorio o vivero para ser inoculados, posteriormente, en áreas degradadas. Finalmente, se identifican los retos futuros para maximizar el éxito de la restauración y conservación de las biocostras.
... According to global change scenarios, their global coverage is expected to decrease dramatically by the end of this century (Rodríguez-Caballero et al., 2018a). Besides this overall reduction in biocrust coverage, climate manipulation experiments also showed that warming, and changes in precipitation patterns (i.e. an increase in the frequency of small water pulses during warm periods) will cause changes in cyanobacteria composition and a reduction of lichen or bryophyte coverage (Maphangwa et al., 2012;Reed et al., 2012;Escolar et al., 2012;García-Pichel et al., 2013;Maestre et al., 2013;Ladrón de Guevara et al., 2014;Ladrón de Guevara et al., 2018), with important implications for ecosystem functioning (Escolar et al., 2012;Maphangwa et al., 2012;Delgado-Baquerizo et al., 2013;Couradeau et al., 2016;Rutherford et al., 2017). Disturbance derived from land use intensification (e.g., trampling) has also been demonstrated to be a relevant threat for biocrusts. ...
Biological soil crusts (biocrusts) form a regular and relevant feature in drylands, as they stabilize the soil, fix nutrients, and influence water cycling. However, biocrust forming organisms have been shown to be dramatically vulnerable to climate and land use change occurring in these regions.
In this study, we used Normalized Difference Vegetation Index (NDVI) data of biocrust-dominated pixels (NDVIbiocrust) obtained from hyperspectral and LANDSAT-7 data to analyse biocrust development over time and to forecast future NDVIbiocrust development under different climate change and livestock density scenarios in southern Africa. We validated these results by analysing the occurrence and composition of biocrusts along a mesoclimatic gradient within the study region.
Our results show that NDVIbiocrust, which reached maximum values of 0.2 and 0.4 in drier and wetter years, respectively, mainly depended on water availability. A predicted decrease in rainfall events according to all future climate scenarios combined with increased temperatures suggested a pronounced decrease in NDVIbiocrust by the end of the 21st century caused by reduced biocrust coverage. Livestock trampling had similar effects and exacerbated the negative impacts of climate change on biocrust coverage and composition. Data assessed in the field concurred with these results, as reduced biocrust cover and a shift from well-developed to early stages of biocrust development were observed along a gradient of decreasing precipitation and increasing temperatures and livestock density.
Our study demonstrates the suitability of multi-temporal series of historical satellite images combined with high-resolution mapping data and Earth system models to identify climate change patterns and their effects on biocrust and vegetation patterns at regional scales.
... As final considerations, the reduction of cover and diversity in lichen-dominated biocrusts is shown to lower the capacity to sequester atmospheric CO 2 [104] while lichens can affect successional processes including the establishment and performance of vascular plants [80,105], and growth form also influences lichen ability to prevent erosion, by retaining soil particles [106,107]. ...
Community ecology has experienced a major transition, from a focus on patterns in taxonomic composition, to revealing the processes underlying community assembly through the analysis of species functional traits. The power of the functional trait approach is its generality, predictive capacity such as with respect to environmental change, and, through linkage of response and effect traits, the synthesis of community assembly with ecosystem function and services. Lichens are a potentially rich source of information about how traits govern community structure and function, thereby creating opportunity to better integrate lichens into ‘mainstream’ ecological studies, while lichen ecology and conservation can also benefit from using the trait approach as an investigative tool. This paper brings together a range of author perspectives to review the use of traits in lichenology, particularly with respect to European ecosystems from the Mediterranean to the Arctic-Alpine. It emphasizes the types of traits that lichenologists have used in their studies, both response and effect, the bundling of traits towards the evolution of life-history strategies, and the critical importance of scale (both spatial and temporal) in functional trait ecology.
... Climate manipulation experiments, in which temperature and/ or precipitation are controlled, are essential for the elucidation of plant adaptation and species interaction responses and mechanisms, and they reduce degrees of uncertainty of vegetation dynamics under specific climate scenarios (Jentsch et al., 2007;Wu et al., 2011;Beier et al., 2012;Langley et al., 2018). For example, empirical experimental data show contrasting spatiotemporal patterns and directions in plant community responses to climate change (Andresen et al., 2016;Estiarte et al., 2016;Harrison et al., 2020), such as increases in biomass accumulation at high latitudes and altitudes (Elmendorf et al., 2012a(Elmendorf et al., ,b, 2015Metcalfe et al., 2018) and decreases in plant growth under dry and arid conditions (Kr€ oel-Dulay et al., 2015;Ladr on de Guevara et al., 2018;Liu et al., 2020). Although changes in species diversity, richness, and composition are expected with increasing temperature and greater variability in precipitation (Knapp et al., 2002;Smith et al., 2009;Komatsu et al., 2019), the temporal patterns of change are not well understood. ...
Grasslands are key repositories of biodiversity and carbon storage and are heavily impacted by effects of global warming and changes in precipitation regimes. Patterns of grassland dynamics associated with variability in future climate conditions across spatiotemporal scales are yet to be adequately quantified. Here, we performed a global meta‐analysis of year and growing season sensitivities of vegetation aboveground biomass (AGB), aboveground net primary productivity (ANPP), and species richness (SR) and diversity (Shannon index, H) to experimental climate warming and precipitation shifts. All four variables were sensitive to climate change. Their sensitivities to shifts in precipitation were correlated with local background water availability, such as mean annual precipitation (MAP) and aridity, and AGB and ANPP sensitivities were greater in dry habitats than in nonwater‐limited habitats. There was no effect of duration of experiment (short vs long term) on sensitivities. Temporal trends in ANPP and SR sensitivity depended on local water availability; ANPP sensitivity to warming increased over time and SR sensitivity to irrigation decreased over time. Our results provide a global overview of the sensitivities of grassland function and diversity to climate change that will improve the understanding of ecological responses across spatiotemporal scales and inform policies for conservation in dry climates.
... Second, and related to the first point, extensive research efforts are being made in order to better understand natural biocrust recovery after disturbance (Nejidat et al., 2016;Concostrina-Zubiri et al., 2017;Xiao et al., 2019). Third, modelling and impact of expected climate change on biocrusts communities has become a strong research line in terms of amount of recent publications and scientific impact (Darrouzet-Nardi et al., 2015;Rutherford et al., 2017;Ladrón de Guevara et al., 2018;Porada et al., 2019). Finally, a better understanding of the services provided to ecosystems (mostly drylands) by biocrust communities, with special emphasis in the enhancement of ecosystems multifunctionality (Delgado-Baquerizo et al., 2016;Liu et al., 2017;Jia et al., 2018;Rodríguez-Caballero et al., 2018b). ...
The Soil Crust International (SCIN) project was a multidisciplinary attempt to obtain a complete understanding of biocrusts communities across Europe, including among the monitored locations the Tabernas badlands in Spain, the driest habitat in the whole continent. Here we provide an overview in a Mini-Review format of our research about the functional performance of the more relevant biocrust forming organisms involved, looking for similarities and differences in the behavior of these communities in regions with contrasting environmental conditions, allowing a deeper understanding of habitat over biocrusts functioning. New unpublished results linked to SCIN are also included in order to reinforce or clarify some general ideas proposed within the text. The general perspective provided to the data through this unique multi-site comparison, will allow in depth studies of relevant functional traits that can shed some light over the possibility of biocrusts behaving as functional types under some circumstances. Poikilohydry is proposed as an essential driving force involved, at different extents, in all key traits ruling biocrusts ecophysiology.
... Meanwhile, warming-triggered moss mortality was likely also a reason for the different effects of warming on lichen-dominated and moss-dominated crusts (Darrouzet-Nardi et al., 2018;Li et al., 2018b). However, other researchers found that 8-year warming reduced the coverage and richness of lichen-dominated crusts while promoting the growth of moss-dominated crusts (Ladrón de Guevara et al., 2018;García-Palacios et al., 2018). Further studies are needed to identify the mechanisms underlying the differential responses of different types of BSCs to warming. ...
Biological soil crusts (BSCs) across desert ecosystems play an important role in modulating terrestrial carbon cycles. Global warming and changes in precipitation patterns are expected to be important triggers for biological activity in BSC-dominated desert ecosystems. Therefore, it is crucial to study the effects of warming and rainfall pulses on soil respiration dynamics at BSC-dominated microsites to predict terrestrial carbon cycling under climate change. In this study, soil respiration rates were monitored continuously during three types of natural precipitation events in lichen-dominated and moss-dominated crusts in both control and warming treatments. Our results revealed that soil respiration was inhibited in BSC-dominated microsites in the warming treatment because of reduced soil water content induced by the warmer conditions, and that the extent of inhibition was lower in the lichen-dominated crusts than in the moss-dominated crusts. During all the precipitation events, soil respiration rates were significantly increased by rainfall pulses and gradually declined thereafter. Over the daily cycle, the clockwise diel hysteresis loop between soil respiration and soil temperature was modified by soil water availability, which was affected by the magnitude of rainfall pulses. Moreover, the effect of photosynthetically active radiation and the mismatch between the depth of carbon dioxide (CO2) production and soil temperature measurement may have contributed to the diel hysteresis pattern. Our results indicated that warming and different types of precipitation events in BSC-dominated desert ecosystems impact soil carbon release through changes in the magnitude of soil respiration.
Aims
One of the most important questions of our time is how ecosystems will be transformed by climate change. Here, we used a five-year field experiment to investigate the effects of climate warming on the cover and function of a sub-Arctic alpine ecosystem in the highlands of Iceland dominated by biocrust, mosses and vascular plants.
Methods
We used Open Top Chambers (OTCs) to simulate warming; standard surface and Normalised Difference Vegetation Index (NDVI) analyses to measure plant cover and function; gas analyzers to monitor biocrust respiration; and the Tea Bag Index approach to estimate mass loss, decomposition and soil carbon stabilization rates.
Results
Contrary to our initial hypothesis of warming accelerating an ecological succession of plants growing on biocrust, we observed a warming-induced decreased abundance of vascular plants and mosses —possibly caused by high temperature summer peaks that resemble heat waves— and an increase in the cover of biocrust. The functional responses of biocrust to warming, including increased litter mass loss and respiration rates and a lower soil carbon stabilization rates, may suggest climate-driven depletion of soil nutrients in the future.
Conclusion
It remains to be studied how the effects of warming on biocrusts from high northern regions could interact with other drivers of ecosystem change, such as grazing; and if in the long-term global change could favor the growth of vascular plants on biocrust in the highlands of Iceland and similar ecosystems. For the moment, our experiment points to a warming-induced increase in the cover and activity of biocrust.
Biocrusts are a prevalent form of living cover in worldwide drylands, and their presence are intimately associated with herbaceous community, forming a spatially mosaic distribution pattern in dryland ecosystems. The role of biocrusts as modulators of herbaceous community assembly is extensively studied, whereas, less is known whether their interactions are permanent or changeable with various environmental conditions. This study conducted a field survey of herbaceous community accompanied by three types of biocrusts (cyanobacterial, cyanobacterial-moss mixed, and moss crusts) in two contrasting (dry and wet) semiarid climate regions in the Chinese Loess Plateau, to explore whether or not climatic aridity gradient affects the interactions between biocrusts and herbaceous community. Our results showed that in dry semiarid climate, the biomass, species richness, and diversity of herbaceous community from biocrust plots were 89 %, 179 %, and 52 % higher than that from the uncrusted plots, respectively, while in wet semiarid climate, those herbaceous community indices from biocrust plots were 68 %, 43 %, and 23 % lower than that from the uncrusted plots, respectively. The impacts of biocrusts on herbaceous community were highly dependent on the types and coverage of biocrusts. Regardless of aridity gradient, the richness and diversity of herbaceous community were the lowest in the moss-covered plots, followed by the cyanobacteria-covered plots and the plots with a mixed cyanobacteria and moss population. Along with increasing biocrust coverage, the species richness and diversity of herbaceous plants initially increased and then decreased in dry semiarid climate, while in wet semiarid climate they decreased linearly with biocrust coverage. Structural equation modeling revealed that the factors of biocrust types and coverage affected herbaceous community indirectly through soil properties in dry semiarid climate, whereas in wet semiarid climate they directly affected herbaceous community through biotic interactions. Together, our findings indicated that cyanobacterial and moss biocrusts facilitate the development of herbaceous community in dry semiarid climate by increasing soil stability and nutrient levels, but in wet semiarid climate they restrict herbaceous plant growth through competing niche space. These results highlight the divergent relationships between biocrusts and herbaceous community across aridity gradient in dryland ecosystems, and this knowledge may be critically important in light of the projected global climate change which is going to change the aridity of global drylands.
Aims
One of the most important questions of our time is how ecosystems will be transformed by climate change. Here, we used a five-year field experiment to investigate the effects of climate warming on the cover and function of a sub-Arctic alpine ecosystem in the highlands of Iceland dominated by biocrust, mosses and vascular plants.
Methods
We used Open Top Chambers (OTCs) to simulate warming; standard surface and NDVI analyses to measure plant cover and function; gas analyzers to monitor biocrust respiration; and the Tea Bag Index approach to estimate mass loss, decomposition and soil carbon stabilization rates.
Results
Contrary to our initial hypothesis of warming accelerating an ecological succession of plants growing on biocrust, we observed a warming-induced decreased abundance of vascular plants and mosses —possibly caused by high temperature summer peaks that resemble heat waves— and an increase in the cover of biocrust. The functional responses of biocrust to warming, including increased litter mass loss and respiration rates and a lower soil carbon stabilization rates, may suggest climate-driven depletion of soil nutrients in the future.
Conclusion
It remains to be studied how the effects of warming on biocrusts from high northern regions could interact with other drivers of ecosystem change, such as grazing; and if in the long-term global change could favor the growth of vascular plants on biocrust in the highlands of Iceland and similar ecosystems. For the moment, our experiment points to a warming-induced increase in the cover and activity of biocrust.
The Lobaria pulmonaria holobiont comprises algal, fungal, cyanobacterial, and bacterial components. We investigated L. pulmonaria’s bacterial microbiome in the adaptation of this ecologically sensitive lichen species to diverse climatic conditions. Our central hypothesis posited that microbiome composition and functionality aligns with continental-scale climatic parameters related to temperature and precipitation. We also tested the impact of short-term weather dynamics, sampling season, and algal/fungal genotypes on microbiome variation. Metaproteomics provided insights into compositional and functional changes within the microbiome. Climatic variables explained 41.64% of microbiome variation, surpassing the combined influence of local weather and sampling season at 31.63%. Notably, annual mean temperature and temperature seasonality emerged as significant climatic drivers. Microbiome composition correlated with algal, not fungal genotype, suggesting similar environmental recruitment for the algal partner and microbiome. Differential abundance analyses revealed distinct protein compositions in sub-atlantic lowland and alpine regions, indicating differential microbiome responses to contrasting environmental/climatic conditions. Proteins involved in oxidative and cellular stress were notably different. Our findings highlight microbiome plasticity in adapting to stable climates, with limited responsiveness to short-term fluctuations, offering new insights into climate adaptation in lichen symbiosis.
This chapter contains detailed information on life cycle, morphology and classification of the three divisions of Bryophytes: Marchantiophyta (liverworts), Bryophyta (mosses) and Anthocerotophyta (hornworts). Additional sections cover the importance of asexual reproduction in Bryophytes, central aspects of their physiology and physiological ecology and the essentials of Bryophyte ecology (autecology, population/community ecology and systems ecology).
Mediterranean drylands are rich in biodiversity and play an important role in global ecosystem sustainable management. This study summarizes the characteristics, dynamic change, and change drivers of Mediterranean drylands. The drylands showed strong spatial heterogeneity, hyperarid and arid regions were dominant in North Africa and West Asia, and semiarid and dry subhumid regions were widely distributed in European countries. Mediterranean dryland is experiencing a warming trend that would become stronger under representative concentration pathways (RCP) 4.5 and 8.5, which would increase the risk of land degradation and desertification. Arid North Africa and West Asia faced rapid population growth that put considerable pressure on food supply and water consumption. The conflicts among land, water, food, and the ecosystem intensified under the warming trend. The significant expansion of cropland and urbanization was widely observed in arid areas, such as Egypt, while the rotation of land reclamation, degradation, abandonment, and reclamation was observed in arid areas and caused large-scale cross-border migration. The Mediterranean region had low food self-sufficiency due to a booming population, and the crop structure of cash crops was dominant. The expansion of cropland also significantly increased the water consumption in the arid area of the Mediterranean region, and water consumption increased by 684.54 × 10 ⁶ m ³ from 2000 to 2020 in Egypt. More robust models and fine spatial resolution data should be developed for the sustainable development of Mediterranean drylands.
Biocrusts are ecosystem engineers in drylands and structure the landscape through their ecohydrological effects. They regulate soil infiltration and evaporation but also surface water redistribution, providing important resources for vascular vegetation. Spatially-explicit ecohydrological models are useful tools to explore such ecohydrological mechanisms, but biocrusts have rarely been included in them. We contribute to closing this gap and assess how biocrusts shape spatio-temporal water fluxes and availability in a dryland landscape and how landscape hydrology is affected by climate-change induced shifts in the biocrust community. We extended the spatially-explicit, process-based ecohydrological dryland model EcoHyD by a biocrust layer which modifies water in- and outputs from the soil and affects surface runoff. The model was parameterized for a dryland hillslope in South-East Spain using field and literature data. We assessed the effect of biocrusts on landscape-scale soil moisture distribution, plant-available water and the hydrological processes behind it. To quantify the biocrust effects, we ran the model with and without biocrusts for a wet and dry year. Finally, we compared the effect of incipient and well-developed cyanobacteria- and lichen biocrusts on surface hydrology to evaluate possible paths forward if biocrust communities change due to climate change. Our model reproduced the runoff source-sink patterns typical of the landscape. The spatial differentiation of soil moisture in deeper layers matched the observed distribution of vascular vegetation. Biocrusts in the model led to higher water availability overall and in vegetated areas of the landscape and that this positive effect in part also held for a dry year. Compared to bare soil and incipient biocrusts, well-developed biocrusts protected the soil from evaporation thus preserving soil moisture despite lower infiltration while at the same time redistributing water toward downhill vegetation. Biocrust cover is vital for water redistribution and plant-available water but potential changes of biocrust composition and cover can reduce their ability of being a water source and sustaining dryland vegetation. The process-based model used in this study is a promising tool to further quantify and assess long-term scenarios of climate change and how it affects ecohydrological feedbacks that shape and stabilize dryland landscapes.
Experimental work suggests that biological soil crusts, dominant primary producers in drylands and tundra, are particularly vulnerable to disturbances that cause reverse ecological succession. To model successional transitions in biocrust communities, we propose a resource-firing game that captures succession dynamics without specifying detailed function forms. The model is evaluated in idealized terrestrial ecosystems, where disturbances are modeled as a reduction in available resources that triggers inter-species competition. The resource-firing game is executed on a finite graph with nodes representing species in the community and a sink node that becomes active when every species is depleted of resources. First, we discuss the theoretical basis of the resource-firing game, evaluate it in the light of existing literature, and consider the characteristics of a biocrust community that has evolved to equilibrium. We then examine the dependence of resource-firing and game stability on species richness, showing that high species richness increases the probability of very short and long avalanches, but not those of intermediate length. Indeed, this result suggests that the response of the community to disturbance is both directional and episodic, proceeding towards reverse succession in bursts of variable length. Finally, we incorporate the spatial structure of the biocrust community into a Cayley Tree and derive a formula for the probability that a disturbance, modeled as a random attack, initiates a large species-death event.
Unlabelled:
Accumulating evidence suggests that warming associated with climate change is decreasing the total amount of soil organic carbon (SOC) in drylands, although scientific research has not given enough emphasis to particulate (POC) and mineral-associated organic carbon (MAOC) pools. Biocrusts are a major biotic feature of drylands and have large impacts on the C cycle, yet it is largely unknown whether they modulate the responses of POC and MAOC to climate change. Here, we assessed the effects of simulated climate change (control, reduced rainfall (RE), warming (WA), and RE + WA) and initial biocrust cover (low (< 20%) versus high (> 50%)) on the mineral protection of soil C and soil organic matter quality in a dryland ecosystem in central Spain for 9 years. At low initial biocrust cover levels, both WA and RE + WA increased SOC, especially POC but also MAOC, and promoted a higher contribution of carbohydrates, relative to aromatic compounds, to the POC fraction. These results suggest that the accumulation of soil C under warming treatments may be transitory in soils with low initial biocrust cover. In soils with high initial biocrust cover, climate change treatments did not affect SOC, neither POC nor MAOC fraction. Overall, our results indicate that biocrust communities modulate the negative effect of climate change on SOC, because no losses of soil C were observed with the climate manipulations under biocrusts. Future work should focus on determining the long-term persistence of the observed buffering effect by biocrust-forming lichens, as they are known to be negatively affected by warming.
Supplementary information:
The online version contains supplementary material available at 10.1007/s10021-022-00779-0.
The complex web of interactions between ecological communities and the physical landscape (biogeomorphology) is being affected by the global scale environmental changes of the Anthropocene. Climate change, habitat destruction, invasions and extinctions are having profound impacts on biogeomorphological process regimes through changes in the composition and activity of ecological communities. However, on the other hand, deliberately-targeted human interventions to biogeomorphic systems have the potential to help mitigate against, and adapt to, the Anthropocene, by managing biogeomorphic processes to enhance resilience. To evaluate these relationships, we propose a conceptual framework based on the ecological concept of functional traits. We review how the Anthropocene is causing changes in species composition, abundance and the prevalence of functional traits to produce changes to biogeomorphic processes and functions that are, as yet, only partly understood. We use examples of fluvial, dryland and coastal biogeomorphic systems to illustrate how purposeful manipulation of biogeomorphic systems (as a type of Nature-based solution) can conserve, enhance or add biogeomorphic functions that are capable of enhancing geomorphic resilience. By focussing on function, this approach offers a range of advantages/avenues for biogeomorphological research. This includes the detection and prediction of human impacts, and an improved understanding of how biogeomorphology can contribute to tackling environmental challenges in the Anthropocene.
Drylands play a significant role in the global biogeochemical cycling of nutrients (carbon, nitrogen, and phosphorus) through abiotic (geological, atmospheric, and hydrological) and biotic (animals, insects, plants, and microorganisms) pathways. They act as important carbon reservoirs and are estimated to store over 30% of the global soil organic carbon reserve. However, nitrogen and phosphorus availability are major limiting factors for biological activity in these oligotrophic environments, affecting community structure, species diversity, and other ecosystem functions (e.g., nutrient cycling and productivity). Nutrient cycling in desert soils is primarily achieved by plant and microbial communities, in particular soil microbial communities, biological soil crusts, hypoliths, and endoliths. Drylands are highly sensitive and prone to disturbance and land degradation resulting from desertification. Changes induced by climate (e.g., precipitation and temperature), structural and temporal variability (nutrient accumulation and distribution of minerals, seasonal variation, and differences in turnover rates), and human activity often alter nutrient cycles that negatively affect the structure and function of these ecosystems (e.g., decreasing carbon storage capacity, increasing NOx emissions, and reducing phosphorus cycling). Comprehending the extent, nature, magnitude, and reversibility of such changes is urgent, given the global importance of drylands in terms of carbon sequestration, greenhouse gas emissions, ecology and biodiversity, and human habitation.
The interest in understanding the role of biocrusts as ecosystem engineers in drylands has substantially increased during the last two decades. Mosses are a major biocrust component that dominate its late successional stages. In general, their impacts on most ecosystem functions are greater than those of early-stage biocrust constituents. However, it is common to find contradictory results regarding how moss interactions with different biotic and abiotic factors affect ecosystem processes. This review aims to: i) describe the adaptations and environmental constraints of biocrust-forming mosses in drylands, ii) identify their primary ecological roles in these ecosystems, and iii) synthesise their responses to climate change. Our review emphasises the importance of interactions between specific functional traits of mosses (e.g., height, radiation reflectance, morphology, shoot densities) with both the environment (e.g., climate, topography and soil properties) and other organisms to understand their ecological roles and responses to climate change. It also highlights key areas that we should research in the future to fulfil essential gaps in our understanding of the ecology and responses to ongoing climate change of biocrust-forming mosses. These include a better understanding of intra- and interspecific interactions and mechanisms driving mosses' carbon balance of during desiccation/rehydration cycles.
The upland and mountainous regions of northern Europe provide a wide variety of ecosystem services. However, these ecosystem services are highly vulnerable to environmental and land-use change. To ensure their future conservation, it is therefore, essential to understand whether upland plant communities will respond positively or negatively to a range of environmental factors such as grazing pressure and landscape-scale factors such as changes in atmospheric SO2 and NOx deposition. To understand this, here, we describe the long-term trends in four UK upland communities (high-level grassland, intermediate grassland, blanket bog, high-level bog) using four replicated long-term experiments examining the effects of sheep grazing compared to no-sheep grazing in Moor House (from 1954 to 2016). Our results showed that species richness and abundance recovered in grazed plots after 2000, with improvements in species richness and abundance of vascular plants, mosses, and liverworts. Unfortunately, no improvement was found for lichens. Species richness, vascular plants, and mosses recovered the fastest, and much faster than liverworts. There was no evidence of slower recovery of species richness and abundance in plots where sheep grazing was removed. These results are consistent with longitudinal studies suggesting recovery after 2000 as a result of reduced atmospheric deposition. Although trends in diversity and abundance in the grazed and ungrazed plots were not identical, they were not markedly different either. The similar richness and abundance trends in the grazed and ungrazed plots found in each plant community suggest that within-community dynamics may overcome initial differences between the grazing treatments over time. In contrast, differences in richness and abundance among plant communities over time suggest that some landscape-scale trends, such as those caused by a reduction in nutrient inputs, initiate community-dependent recovery.
Background and Aims：The outstanding ability of biological soil crusts (BSCs) in soil microenvironments regulation is mainly attribute to microorganisms that colonizing in biocrusts. We aimed to investigate the changes of bacterial community structure and function with biocrust succession, as well as their responses to climatic changes across large geographical scales.
Methods: Algal BSCs and lichen BSCs were sampled along an aridity gradient on alpine grasslands. Bacterial communities in biocrusts were measured using high-throughput sequencing, and soil underlying biocrusts (0-5 cm) was collected for nutrients determination.
Results: Our results indicated that compared with algal BSCs, bacterial community in lichen BSCs was characterized by lower diversity, more complex co-occurrence network and mutually beneficial relationships. The bacterial community assembly was governed mainly by stochastic processes for lichen BSCs, which was different from the almost equally important roles of stochastic and deterministic processes for algal BSCs. Geographical location had a significant effect on bacterial communities in both algal and lichen BSCs, while had a greater effect on lichen BSCs. It is noteworthy that the bacterial diversity of algal BSCs was positively correlated with aridity index, while that of lichens was negatively correlated with aridity index. Moreover, we determined lower soil pH and higher soil phosphorus content underlying lichen BSCs, implying their advantages in soil improvement.
Conclusions: Aridity index was one of important driving factors of bacterial community in biocrusts, and its effects were biocrust type dependent. Lichen BSCs had greater effects on soil improvement than that of algal BSCs.
Biological soil crusts (BSCs) develop when various combinations of diminutive cyanobacteria, eukaryotic algae, non-lichenized fungi, lichens, and/or bryophytes occupy the upper few millimeters of the soil and raw material. They can be present in a wide range of ecological, including successional, and climatic conditions when and where disturbance and/or aridity have resulted in opportunities for colonization. However, they are most prevalent in arid, semiarid and polar ecosystems where vascular plant cover and diversity are characteristically low, leaving large areas available for colonization by some combination of the organismal groups mentioned above. The ecological roles of BSCs are numerous and diverse, and include the collection, accumulation and cycling of essential airborne and soil nutrients, redistribution of precipitated water, and soil formation and stabilization.
Biocrusts (topsoil communities formed by mosses, lichens, bacteria, fungi, algae, and cyanobacteria) are a key biotic component of dryland ecosystems. Whilst climate patterns control the distribution of biocrusts in drylands worldwide, terrain and soil attributes can influence biocrust distribution at landscape scale. Multi‐source UAV imagery was used to map and study biocrust ecology in a typical dryland ecosystem in central Spain. RGB imagery was processed using Structure from Motion techniques to map terrain attributes related to microclimate and terrain stability. Multispectral imagery was used to produce accurate maps (accuracy > 80%) of dryland ecosystem components (vegetation, bare soil and biocrust composition). Finally, thermal infrared (TIR) and multispectral imagery was used to calculate the apparent thermal inertia (ATI) of soil and to evaluate how ATI was related to soil moisture (r2= 0.83). The relationship between soil properties and UAV‐derived variables was first evaluated at the field plot level. Then, the maps obtained were used to explore the relationship between biocrusts and terrain attributes at ecosystem level through a redundancy analysis. The most significant variables that explain biocrust distribution are: ATI (34.4% of variance, F= 130.75; p<0.001), Elevation (25.8%, F=97.6; p<0.001), and potential incoming solar radiation (PSIR) (52.9%, F=200.1; p<0.001). Differences were found between areas dominated by lichens and mosses. Lichen‐dominated biocrusts were associated with areas with high slopes and low values of ATI, with soil characterized by a higher amount of soluble salts, and lower amount of organic carbon, total phosphorus (Ptot) and total nitrogen (Ntot). Biocrust‐forming mosses dominated lower and moister areas, characterised by gentler slopes and higher values of ATI with soils with higher contents of organic carbon, Ptot and Ntot. This study shows the potential to use UAVs to improve our understanding of drylands and to evaluate the control that the terrain has on biocrust distribution.
Lichens are unequivocally responding to global change. Direct effects are so far apparent during the past three decades (since c. 1990) and in the temperate regions only. Interestingly, contrasting responses of lichens and other cryptogams to recent changes have been reported. Lichens have indirectly suffered from global change effects in arctic regions. In this chapter, predicted, observed, and uncertain effects related to lichen and climate change are discussed together with the habitats of vulnerable lichens, with special attention to mountain tops in the tropics—the most likely place for possible extinction of lichens as a result of global warming. The most severe effects of climate change, leading to probable extinctions, is expected (but has not been observed as yet) on high mountains in tropical regions.
Despite the high relevance of communities dominated by lichens, mosses and cyanobacteria living on the soil surface (biocrusts) for ecosystem functioning in drylands, no study to date has investigated the decomposition of biocrust-forming lichen litter in situ. Thus, we do not know whether the drivers of its decomposition are similar to those for plant litter (for example, importance of abiotic degradation through UV radiation), the magnitude of lichen decomposition rates and whether they will be affected by ongoing climate change. Here we report the results from a litter decomposition experiment carried out with two biocrust-forming lichens (Diploschistes diacapsis and Cladonia convoluta) that differ in litter chemical quality (C:N ratio) in central Spain. We evaluated how lichen decomposition was affected by warming, rainfall exclusion and their combination. We also manipulated the incidence of UV radiation using mesh material that blocked 10% or 90% of incoming UV radiation. Our results indicate that lichens decompose as fast as some plants typical of the study area (k ~ 0.3 y−1). We observed differences among the species studied in line with what is expected according to their chemical composition. Warming increased decomposition rates of both lichen species by 28% and mediated the effects of photodegradation. Although UV exposure accelerated the decomposition of D. diacapsis, it slowed that of C. convoluta. Our results indicate that biocrust-forming lichens can decompose in the field at a rate similar to that of vascular plants and that this process will be affected by warming. The findings presented emphasize the need of considering biocrusts and the decomposition of their tissues when honing ecosystem models aiming to forecast carbon cycling responses to climate change in drylands.
This review describes the latest progress of dryland ecosystem dynamic change in the Mediterranean region. Recent findings indicate that extent of dryland in the Mediterranean region has been expanding in the past decades and will continue to expand in the coming decades due to the stronger warming effect than other regions. The warming trend with intensified human activities has generated a series of negative impacts on productivity, biodiversity, and stability of the dryland ecosystem in Mediterranean region. Increased population, overgrazing and, grazing abandonment intensified the land degradation and desertification. The coverage, richness, and abundance of biological soil crust have been reduced due to the decline of soil water availability and increased animals. Future studies are required to further our understanding of the process and mechanism of the dryland dynamics, including the identification of essential variables, discriminating human and climate-induced changes, and modeling future trajectories of dryland changes.
Biological soil crust (BSC) is a key biotic factor in desert areas and can significantly alter nutrient cycling. The interaction between seasonal climatic change and BSC can further modify nutrient cycling. Thus far, limited information has been provided regarding the effect of BSC on net soil nitrogen (N) transformation and their seasonal pattern in temperate desert areas. Therefore, we assessed the seasonal patterns of net soil N mineralization and nitrification in three microhabitats (moss-covered, cyanobacteria-lichen-covered, and bare soils) from October 2011 to September 2012 by using an intact soil core in situ incubation method. Seasonal variations in inorganic N pools, net N mineralization, and nitrification rates were observed. The seasonal patterns of net N transformation rates were greatly modified by soil temperature and moisture (highest in August and lowest in January). During non-growing season, net N immobilization was observed in the three microsites; a higher inorganic N content was observed in the moss-covered soil than in other soils. BSC increased the net soil N transformation rates during the early growing season but reduced the inorganic N content during the peak growing season. On the basis of these findings, we concluded that seasonal variation in climate significantly affected N transformation. The colonization and the development of BSC stimulated N cycling and storage in arid desert systems.
Supporting Information of the paper: Warming reduces the cover, richness and evenness of lichen-dominated biocrusts but promotes moss growth: Insights from an eight-year experiment
Biocrusts are model ecosystems of global change studies. However, light and non-rainfall water (NRW) were previously few considered. Different biocrust types further aggravated the inconsistence. So carbon-exchange of biocrusts (cyanobacteria crusts-AC1/AC2; cyanolichen crust-LC1; chlorolichen crust-LC2; moss crust-MC) utilizing NRW at various temperatures and light-intensities were determined under simulated and insitu mesocosm experiments. Carbon input of all biocrusts were negatively correlated with experimental temperature under all light-intensity with saturated water and stronger light with equivalent NRW, but positively correlated with temperature under weak light with equivalent NRW. LCPs and R/Pg of AC1 were lowest, followed in turn by AC2, LC2 and MC. Thus AC1 had most opportunities to use NRW, and 2.5 °C warming did cause significant changes of carbon exchange. Structural equation models further revealed that air-temperature was most important for carbon-exchange of ACs, but equally important as NRW for LC2 and MC; positive influence of warming on carbon-input in ACs was much stronger than the latter. Therefore, temperature effect on biocrust carbon-input depends on both moisture and light. Meanwhile, the role of NRW, transitional states between ACs, and obvious carbon-fixation differences between lichen crusts should be fully considered in the future study of biocrusts responding to climate change.
The loss of biological soil crusts represents a challenge for the restoration of disturbed environments, specifically in particular substrates hosting unique lichen communities. However, the recovery of lichen species affected by mining is rarely addressed in restoration projects. Here, we evaluate the translocation of Diploschistes diacapsis, a representative species of gypsum lichen communities affected by quarrying. We tested how a selection of adhesives could improve thallus attachment to the substrate and affect lichen vitality (as CO2 exchange and fluorescence) in rainfall-simulation and field experiments. Treatments included: white glue, water, hydroseeding stabiliser, gum arabic, synthetic resin, and a control with no adhesive. Attachment differed only in the field, where white glue and water performed best. Adhesives altered CO2 exchange and fluorescence yield. Notably, wet spoils allowed thalli to bind to the substrate after drying, revealing as the most suitable option for translocation. The satisfactory results applying water on gypsum spoils are encouraging to test this methodology with other lichen species. Implementing these measures in restoration projects would be relatively easy and cost-effective. It would help not only to recover lichen species in the disturbed areas but also to take advantage of an extremely valuable biological material that otherwise would be lost.
The loss of biological soil crusts represents a challenge for the restoration of disturbed environments, specifically in particular substrates hosting unique lichen communities. However, the recovery of lichen species affected by mining is rarely addressed in restoration projects. Here, we evaluate the translocation of Diploschistes diacapsis, a representative species of gypsum lichen communities affected by quarrying. We tested how a selection of adhesives could improve thallus attachment to the substrate and affect lichen vitality (as CO2 exchange and fluorescence) in rainfall-simulation and field experiments. Treatments included: white glue, water, hydroseeding stabiliser, gum arabic, synthetic resin, and a control with no adhesive. Attachment differed only in the field, where white glue and water performed best. Adhesives altered CO2 exchange and fluorescence yield. Notably, wet spoils allowed thalli to bind to the substrate after drying, revealing as the most suitable option for translocation. The satisfactory results applying water on gypsum spoils are encouraging to test this methodology with other lichen species. Implementing these measures in restoration projects would be relatively easy and cost-effective. It would help not only to recover lichen species in the disturbed areas but also to take advantage of an extremely valuable biological material that otherwise would be lost.
Consequences of shifting species distributions
Climate change is causing geographical redistribution of plant and animal species globally. These distributional shifts are leading to new ecosystems and ecological communities, changes that will affect human society. Pecl et al. review these current and future impacts and assess their implications for sustainable development goals.
Science , this issue p. eaai9214
Drylands represent the planet’s largest terrestrial biome, and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts) ‒ soil-surface communities of lichens, mosses, and/or cyanobacteria ‒ comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness—changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+4oC above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (>30 %). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate.
Understanding how drylands respond to ongoing environmental change is extremely important for global sustainability. In this review, we discuss how biotic attributes, climate, grazing pressure, land cover change, and nitrogen deposition affect the functioning of drylands at multiple spatial scales. Our synthesis highlights the importance of biotic attributes (e.g., species richness) in maintaining fundamental ecosystem processes such as primary productivity, illustrates how nitrogen deposition and grazing pressure are impacting ecosystem functioning in drylands worldwide, and highlights the importance of the traits of woody species as drivers of their expansion in former grasslands. We also emphasize the role of attributes such as species richness and abundance in controlling the responses of ecosystem functioning to climate change. This knowledge is essential to guide conservation and restoration efforts in drylands, as biotic attributes can be actively managed at the local scale to increase ecosystem resilience to global change. Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics Volume 47 is November 01, 2016. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
Biological soil crusts (BSCs) are small-scale communities of lichens, mosses, algae, and cyanobacteria that cover much of the surface area in regions where vascular plant growth is restricted due to harsh environmental conditions, such as perpetually ice-free areas in terrestrial Antarctic environments and alpine areas above the tree line. To our knowledge, none of the available studies provides a direct Antarctic-alpine comparison of BSC activity periods and the water use, both key traits to understand their physiological behavior and therefore related growth and fitness. Here, activity patterns and water relations were studied at two sites, one in continental Antarctica (Garwood Valley 78°S) and one in the High Alps of Austria (Hochtor, Großglockner 2350m). BSCs in continental Antarctica were only rarely active, and if so, then during melt after snowfalls and by fog. In the Austrian Alps, BSCs were continuously active and additionally activated by rainfall, fog, and dew. Consequently, high alpine BSCs can be expected to have much higher photosynthetic productivity supporting higher growth rates than the same functional vegetation unit has in continental Antarctica.
Soil surface temperature, an important driver of terrestrial biogeochemical processes, depends strongly on soil albedo, which can be significantly modified by factors such as plant cover. In sparsely vegetated lands, the soil surface can be colonized by photosynthetic microbes that build biocrust communities. Here we use concurrent physical, biochemical and microbiological analyses to show that mature biocrusts can increase surface soil temperature by as much as 10 °C through the accumulation of large quantities of a secondary metabolite, the microbial sunscreen scytonemin, produced by a group of late-successional cyanobacteria. Scytonemin accumulation decreases soil albedo significantly. Such localized warming has apparent and immediate consequences for the soil microbiome, inducing the replacement of thermosensitive bacterial species with more thermotolerant forms. These results reveal that not only vegetation but also microorganisms are a factor in modifying terrestrial albedo, potentially impacting biosphere feedbacks on past and future climate, and call for a direct assessment of such effects at larger scales.
Drylands are home to more than 38% of the total global population and are one of the most sensitive areas to climate change and human activities1, 2. Projecting the areal change in drylands is essential for taking early action to prevent the aggravation of global desertification3, 4. However, dryland expansion has been underestimated in the Fifth Coupled Model Intercomparison Project (CMIP5) simulations5 considering the past 58 years (1948–2005). Here, using historical data to bias-correct CMIP5 projections, we show an increase in dryland expansion rate resulting in the drylands covering half of the global land surface by the end of this century. Dryland area, projected under representative concentration pathways (RCPs) RCP8.5 and RCP4.5, will increase by 23% and 11%, respectively, relative to 1961–1990 baseline, equalling 56% and 50%, respectively, of total land surface. Such an expansion of drylands would lead to reduced carbon sequestration and enhanced regional warming6, 7, resulting in warming trends over the present drylands that are double those over humid regions. The increasing aridity, enhanced warming and rapidly growing human population will exacerbate the risk of land degradation and desertification in the near future in the drylands of developing countries, where 78% of dryland expansion and 50% of the population growth will occur under RCP8.5.
Studies of cryptogam responses to climate change in the polar regions are scarce because these slow-growing organisms require long-term monitoring studies. Here, we analyse the response of a lichen and moss community to 10 years of passive environmental manipulation using open-top chambers (OTCs) in the maritime Antarctic region. Cover of the dominant lichen Usnea antarctica declined by 71 % in the OTCs. However, less dominant lichen species showed no significant responses except for an increase in Ochrolechia frigida, which typically covered dying lichen and moss vegetation. There were no detectable responses in the moss or associated micro-arthropod communities to the influence of the OTCs. Based on calculated respiration rates, we hypothesise that the decline of U. antarctica was most likely caused by increased net winter respiration rates (11 %), driven by the higher temperatures and lower light levels experienced inside the OTCs as a result of greater snow accumulation. During summer, U. antarctica appears unable to compensate for this increased carbon loss, leading to a negative carbon balance on an annual basis, and the lichen therefore appears to be vulnerable to such climate change simulations. These findings indicate that U. antarctica dominated fell-fields may change dramatically if current environmental change trends continue in the maritime Antarctic, especially if associated with increases in winter snow depth or duration.
Significance
In drylands worldwide, where plant cover is sparse, large amounts of the ground surface are covered by specialized organisms that form biological soil crusts (biocrusts). Biocrusts fix carbon and nitrogen, stabilize soils, and influence hydrology. Extensive physical disturbance from livestock/human trampling and off-road vehicles is known to destroy biocrusts and alter ecosystem function. More recent work also indicates that climate change can affect biocrust communities. Contrary to our expectations, experimental climate change and physical disturbance had strikingly similar impacts on biocrust communities, with both promoting a shift to degraded, early successional states. These results herald ecological state transitions in drylands as temperatures rise, calling for management strategies that consider risks from both physical disturbances and climate change.
Soil communities dominated by lichens and mosses (biocrusts) play key roles in maintaining ecosystem structure and functioning in drylands worldwide. However, few studies have explicitly evaluated how climate change-induced impacts on biocrusts affect associated soil microbial communities. We report results from a field experiment conducted in a semiarid Pinus halepensis plantation, where we setup an experiment with two factors: cover of biocrusts (low [<15%] versus high [>50%]), and warming (control versus a ∼2°C temperature increase). Warming reduced the richness and cover (∼45%) of high biocrust cover areas 53 months after the onset of the experiment. This treatment did not change the ratios between the major microbial groups, as measured by phospholipid fatty acid analysis. Warming increased the physiological stress of the Gram negative bacterial community, as indicated by the cy17:0/16:1ω7 ratio. This response was modulated by the initial biocrust cover, as the increase in this ratio with warming was higher in areas with low cover. Our findings suggest that biocrusts can slow down the negative effects of warming on the physiological status of the Gram negative bacterial community. However, as warming will likely reduce the cover and diversity of biocrusts, these positive effects will be reduced under climate change.
Plant biodiversity is often correlated with ecosystem functioning in terrestrial ecosystems. However, we know little about the relative and combined effects of above- and belowground biodiversity on multiple ecosystem functions (e.g., ecosystem multifunctionality, EMF) or how climate might mediate those relationships. Here, we tease apart the effects of biotic and abiotic factors, both above and belowground, on EMF on the Tibetan Plateau, China. We found that a suite of biotic and abiotic variables account for up to 86% of the variation in EMF, with the combined effects of above- and belowground biodiversity accounting for 45% of the variation in EMF. Our results have two important implications: first, including belowground biodiversity in models can improve the ability to explain and predict EMF. Second, regional-scale variation in climate, and perhaps climate change, can determine or at least modify, the effects of biodiversity on EMF in natural ecosystems.
In arid and semiarid ecosystems, plant interspaces are frequently covered by communities of cyanobacteria, algae, lichens and mosses, known as biocrusts. These crusts often act as runoff sources and are involved in soil stabilization and fertility, as they prevent erosion by water and wind, fix atmospheric C and N and contribute large amounts of C to soil. Their contribution to the C balance as photosynthetically active surfaces in arid and semiarid regions is receiving growing attention. However, very few studies have explicitly evaluated their contribution to organic carbon (OC) lost from runoff and erosion, which is necessary to ascertain the role of biocrusts in the ecosystem C balance. Furthermore, biocrusts are not resilient to physical disturbances, which generally cause the loss of the biocrust and thus, an increase in runoff and erosion, dust emissions, and sediment and nutrient losses. The aim of this study was to find out the influence of biocrusts and their removal on dissolved and sediment organic carbon losses. One-hour extreme rainfall simulations (50 mm h–1) were performed on small plots set up on physical soil crusts and three types of biocrusts, representing a development gradient, and also on plots where these crusts were removed from. Runoff and erosion rates, dissolved organic carbon (DOC) and organic carbon bonded to sediments (SdOC) were measured during the simulated rain. Our results showed different SdOC and DOC for the different biocrusts and also that the presence of biocrusts substantially decreased total organic carbon (TOC) (average 1.80±1.86 g m–2) compared to physical soil crusts (7.83±3.27 g m–2). Within biocrusts, TOC losses decreased as biocrusts developed, and erosion rates were lower. Thus, erosion drove TOC losses while no significant direct relationships were found between TOC losses and runoff. In both physical crusts and biocrusts, DOC and SdOC concentrations were higher during the first minutes after runoff began and decreased over time as nutrient-enriched fine particles were washed away by runoff water. Crust removal caused a strong increase in water erosion and TOC losses. The strongest impacts on TOC losses after crust removal occurred on the lichen plots, due to the increased erosion when they were removed. DOC concentration was higher in biocrust–removed soils than in intact biocrusts, probably because OC is more strongly retained by BSC structures, but easily blown away in soils devoid of them. However, SdOC concentration was higher in intact than removed biocrusts associated with greater OC content in the top crust than in the soil once the crust is scraped off. Consequently, the loss of biocrusts leads to OC impoverishment of nutrient–limited interplant spaces in arid and semiarid areas and the reduction of soil OC heterogeneity, essential for vegetation productivity and functioning of this type of ecosystems.
In this paper a novel multivariate method is proposed for the analysis of community response data from designed experiments repeatedly sampled in time. The long-term effects of the insecticide chlorpyrifos on the invertebrate community and the dissolved oxygen (DO)–pH–alkalinity–conductivity syndrome, in outdoor experimental ditches, are used as example data. The new method, which we have named the principal response curve method (PRC), is based on redundancy analysis (RDA), adjusted for overall changes in community response over time, as observed in control test systems. This allows the method to focus on the time-dependent treatment effects. The principal component is plotted against time, yielding a principal response curve of the community for each treatment. The PRC method distills the complexity of time-dependent, community-level effects of pollutants into a graphic form that can be appreciated more readily than the results of other currently available multivariate techniques. The PRC method also enables a quantitative interpretation of effects towards the species level.
The Soil Crust International project aims to better understand the functioning of biological soil crust environments (BSC) in Europe in order to understand the importance of these ecosystems. The final objective of this project is to inform and strengthen protection strategies for these types of habitats in the frame of the European Union. To achieve this, four different soil crust regions have been chosen in Europe following latitudinal and altitudinal gradients. The work presented here is based on the simultaneous monitoring of gas exchange, chlorophyll fluorescence and microclimate of the most abundant BSC in one of these four locations, the Tabernas badlands, Almeria, SE Spain, one of the driest regions in Europe. The five BSC types monitored are dominated by the lichen species Squamarina cartilaginea, Diploschistes diacapsis, Toninia albilabra and Psora decipiens and by the moss Didymodon rigidulus. We aim to understand the conditions in which the BSC are metabolically active in order to get a better knowledge about the contribution of the BSC to the carbon budget of the ecosystem. Our first results after nearly 1 year of chlorophyll fluorescence and microclimatic monitoring linked to gas exchange data during typical activity days obtained in the field suggest similar physiological performance between the different BSC types studied. BSC were active under suboptimal conditions, and activity duration was not different whether measured by chlorophyll a fluorescence or CO2 gas exchange, a relationship that will be the basis of a productivity model.
Understanding functional diversity is critical to manage and preserve biodiversity
and ecosystem functioning in the face of global change. However, the efforts to
characterize this functional component have been mostly directed to vascular vegetation.
We sampled lichen-dominated biological soil crusts (BSCs) in semiarid grasslands along
an environmental gradient in the Iberian Peninsula. We characterized five effect functional
traits for 31 lichens species, and evaluated the influence of large scale (i.e. precipitation)
and small scale factors (i.e. substrate type, shrub presence, Stipa tenacissima presence) on
dominant trait values; i.e. community weighted means, and functional divergence; i.e. Rao
quadratic entropy in 580 sampling quadrats. Across the gradient, we found multiple trait
shifts and a general increase of functional divergence with increasing precipitation. We
also observed that substrate type and small scale biotic factors determined shifts in all traits
studied, while these factors affected less to functional divergence. Comparing functional
diversity with taxonomic diversity, we found contrasting responses to both large and small
scale factors. These findings suggest that BSC community trait composition is influenced
by multi-scale abiotic and biotic factors with environmental filtering dominating at large
spatial scales and limiting similarity at specific small scales. Also, our results emphasize
the potential differences between taxonomic and functional diversity in response to
environmental factors. We concluded that functional diversity of BSCs not only provides
novel and critical knowledge of BSC community structure, but also it should be considered as a critical tool in biodiversity conservation strategies, ecosystem services assessment and
ecological modelling.
Soil surface communities dominated by mosses, lichens and cyanobacteria (biocrusts) are common between vegetation patches in drylands worldwide, and are known to affect soil wetting and drying after rainfall events. While ongoing climate change is already warming and changing rainfall patterns of drylands in many regions, little is known on how these changes may affect the hydrological behaviour of biocrust-covered soils. We used eight years of continuous soil moisture and rainfall data from a climate change experiment in central Spain to explore how biocrusts modify soil water gains and losses after rainfall events under simulated changes in temperature (2.5°C warming) and rainfall (33% reduction). Both rainfall amount and biocrust cover increased soil water gains after rainfall events, whereas experimental warming, rainfall intensity and initial soil moisture decreased them. Initial moisture, maximum temperature and biocrust cover, by means of enhancing potential evapotranspiration or by soil darkening, increased the drying rates and enhanced the exponential behaviour of the drying events. Meanwhile, warming reduced their exponential behaviour. The effects of climate change treatments on soil water gains and losses changed through time, with important differences between the first two years of the experiment and five years after its setup. These effects were mainly driven by the important reductions in biocrust cover and diversity observed under warming. Our results highlight the importance of long-term studies to understand soil moisture responses to ongoing climate change in drylands.
This volume summarizes our current understanding of biological soil crusts (biocrusts), which are omnipresent in dryland regions. Since they cover the soil surface, they influence, or even control, all surface exchange processes. Being one of the oldest terrestrial communities, biocrusts comprise a high diversity of cyanobacteria, algae, lichens and bryophytes together with uncounted bacteria, and fungi. The authors show that biocrusts are an integral part of dryland ecosystems, stabilizing soils, influencing plant germination and growth, and playing a key role in carbon, nitrogen and water cycling. Initial attempts have been made to use biocrusts as models in ecological theory. On the other hand, biocrusts are endangered by local disruptions and global change, highlighting the need for enhanced recovery methods. This book offers a comprehensive overview of the fascinating field of biocrust research, making it indispensable not only for scientists in this area, but also for land managers, policy makers, and anyone interested in the environment.
Cyanobacteria are a key constituent of biocrusts, communities dominated by lichens, mosses and associated microorganisms, which are prevalent in drylands worldwide and that largely determine their functioning. Despite their importance, there are large gaps in our knowledge of the composition and diversity of cyanobacteria associated with biocrusts, particularly in areas such as the Mediterranean Basin. We studied the diversity of these cyanobacteria in a gypsiferous grassland from Central Spain using both morphological identification after cultivation and genetic analyses with the 16 S rRNA gene. Nine different morphotypes were observed, eight corresponding to filamentous, and one to unicellular cyanobacteria. We found cyanobacterial genera typical of biocrust communities, such as Microcoleus and Trichocoleus, and N-fixing cyanobacteria such as Scytonema and Nostoc. Genetic information allowed us to identify cultures belonging to recently described genera such as Roholtiella, Nodosilinea and Mojavia. We also describe two new phylotypes of Microcoleus and Scytonema, which are key genera contributing to ecosystem functioning in biocrust-dominated ecosystems worldwide.
Biological soil crusts (hereafter, “biocrusts”) dominate soil surfaces in nearly all dryland environments. To better understand the influence of water content on carbon (C) exchange, we assessed the ability of dual-probe heat-pulse (DPHP) sensors, installed vertically and angled, to measure changes in near-surface water content. Four DPHP sensors were installed in each of two research plots (eight sensors total) that differed by temperature treatment (control and heated). Responses were compared to horizontally installed water content measurements made with three frequency-domain reflectometry (FDR) sensors in each plot at 5-cm depth. The study was conducted near Moab, Utah, from April through September 2009. Results showed significant differences between sensor technologies: peak water content differences from the DPHP sensors were approximately three times higher than those from the FDR sensors; some of the differences can be explained by the targeted monitoring of biocrust material in the shorter DPHP sensor and by potential signal loss from horizontally installed FDR sensors, or by an oversampling of deeper soil. C-exchange estimates using the DPHP sensors showed a net C loss of 69 and 76 g C m⁻² in control and heated plots, respectively. The study illustrates the potential for using the more sensitive data from shallow installations for estimating C exchange in biocrusts.
Drylands, a critical terrestrial system of the Earth due to low water availability, are known for their extensive global reach, estimated by most scientific sources at approximately 41% of the world's land area, or ~ 60 mil km². However, the analysis of the global dryland areas, using new climate data, suggests a total of ~ 45% of the Earth's terrestrial area, almost 7 mil km² more than initially estimated. This new spatial dimension involves a wide range of environmental issues, some of which have yet to be associated with these critical global systems. This paper primarily aims to accurately quantify the global, continental and national extent of drylands by using a high-resolution climate database presently available at global level. Also, based on relevant scientific literature, this approach attempts to briefly highlight the main environmental issues (natural and anthropogenic) of the major continental and regional dryland areas. In this respect, special attention was given to the land degradation processes (water and wind erosion, vegetation degradation, salinization, soil compaction and nutrient loss), as it is known to be the main environmental perturbation in almost all dryland systems. Research shows that, given the fact that Africa and Asia have the most extensive dryland systems on Earth (each of them has almost 23 mil km², or ~ 15% of the global land area), these continents are especially threatened by major environmental perturbations (desertification, in addition to other ecological and climatic disturbances such as drought, dust storms, heat waves, water stress, extreme rainfall events, wildfire, dzud, or disease emergence), which are currently affecting 46 African states (37% of the 126 states affected by aridity worldwide) and 38 Asian states (30%). Given this context, anthropogenic systems are indirectly severely threatened by the crisis generated by soaring poverty, food insecurity, population migration, and escalating conflicts and regional political instability. Moreover, in the current context of large-scale aridity identified at high latitudes, another critical threat reviewed was the cryosphere's destabilization, which can potentially accelerate climate warming by means of positive feedback mechanisms that can be triggered in the global climate system. In this respect, a major concern is attributed to permafrost melting that, against the background of a significant expansion in the terrestrial northern hemisphere (in Russia, Alaska and Canada), can generate a massive acceleration of climate warming due to the potential release of large quantities of carbon dioxide (CO2) and methane (CH4), which are currently stored in these frozen soils in the Arctic and sub-Arctic regions.
Land degradation by erosion is especially important in drylands, which are among the most vulnerable to disturbance by human activity or climate change. Biocrusts are an essential surface component of these ecosystems and one of the most important contributors to surface resistance and stability, and therefore, keeping soil fertile in these nutrient-limited-environments. Loss of biocrusts can result in increased sediment losses and subsequent loss of soil organic carbon (SOC) and other soil resources, which are vital for vegetation and general ecosystem functioning. Despite their importance, the consequences of biocrust loss on sediment and SOC losses in drylands have been poorly analysed. In this study, we examined the influence of two biocrust types (cyanobacteria and lichen-dominated biocrusts) and biocrust removal on runoff and sediment yield, from natural rainfall during one hydrological year in a semiarid badlands catchment (Tabernas, SE Spain). The influence of biocrust type and biocrust removal on SOC losses from water erosion (dissolved and sediment organic carbon losses, DOC and SdOC, respectively) was also analysed. Our results show that sediment yield significantly increased after biocrust removal, especially during the first rain after biocrust removal, when particles were left directly exposed to raindrop impact and easily washed away by runoff. Annual sediment yield was 465, 75 and 24 g m− 2 in biocrust-removed, cyanobacteria-covered and lichen-covered soil, respectively, and the first event represented 87% of annual sediment losses on biocrust-removed plots. Biocrust removal was accompanied by a significant increase in both DOC and SdOC mobilisation. Total organic carbon (TOC) mobilisation was the highest in soils where the biocrust had been removed and decreased as the biocrust was more developed. Annual TOC mobilisation was 10.2, 3.0 and 1.4 g m− 2 in biocrust-removed, cyanobacteria-covered and lichen-covered soil, respectively. TOC mobilisation was mainly driven by sediments and thus, 89% of annual TOC mobilisation occurred during the first rain after biocrust removal. The high sediment and SOC losses recorded after biocrust removal emphasize the importance of biocrust conservation for avoiding the loss of soil resources and maintaining fertility in interplant soils in drylands.
In low-nutrient environments with few vascular plant symbiotic N fixers, biocrusts play an important role in ecosystem N cycling. A large number of studies across a wide range of biomes clearly confirm that not only the presence of biocrusts but biocrust community composition strongly influences N-fixation activity, with N fixation increasing with level of development (cyanobacterial-lichen biocrusts > dark cyanobacterial biocrust (e.g., Nostoc spp. and Collema spp.) > light Microcoleus-dominated biocrust). Nitrogen fixation by biocrusts results in N release to the soil in a variety of N forms (inorganic and organic N), thus elevating soil inorganic N pools in the top few millimeters of soil. The influence of N release on the bulk soil at greater soil depths is less clear, with biocrusts either elevating or having no influence on bulk soil inorganic N pools. The fate of N fixed and released by biocrusts, and whether this N is retained in the ecosystem in either soils or plants, determines ecosystem N balance over longer time scales, and results on the influence of biocrusts are mixed. Whereas we have multiple studies that examine a single compartment of N budgets, we lack studies that simultaneously address N inputs, losses, and soil and plant pools, thus precluding the construction of definitive N balances. One of the most consistent impact biocrusts have on ecosystem N is reducing N loss via wind and water erosion, with such losses consistently decreasing with increasing biocrust development.
Biological soil crusts (biocrusts) are heterogeneously distributed in space, and the drivers of their distribution depend on the spatial scale of observation. Globally, there are about 1544 cyanobacteria, algae, bryophyte, and lichen species reported as components of biocrusts. At the global scale, the degree and age of isolation of land masses may dictate distribution of these species and the similarities of the floras of different continents. At intracontinental and smaller scales, climate strongly influences abundance and community composition of biocrusts. Within drylands, biocrusts become more abundant and diverse with increases in precipitation. The seasonality of rainfall is about equally important, with regions receiving the most precipitation in winter exhibiting the highest abundance. At ecoregional and smaller scales, edaphic gradients become particularly influential. The most significant soil properties influencing the cover, richness, and composition of biocrusts in dryland environments are soil texture, pH, and calcareousness. Additionally, gypsiferous soils are often associated with distinct floras and high abundance and diversity of biocrusts, especially lichens. At local to microscales, biocrusts often are better developed in habitats with lower radiation loads such as polar-oriented slopes or shaded habitats. Also at small scales, vascular plant canopies buffer microclimate for biocrusts, but also can exert negative influences such as burial by litter. While our knowledge of biocrust distribution has advanced rapidly, there are considerable geographic and taxonomic gaps in our knowledge and a pronounced lack of truly global studies.
A wide range of studies show global environmental change will profoundly affect the structure, function, and dynamics of terrestrial ecosystems. The research synthesized here underscores that biocrust communities are also likely to respond significantly to global change drivers, with a large potential for modification to their abundance, composition, and function. We examine how elevated atmospheric CO2 concentrations, climate change (increased temperature and altered precipitation), and nitrogen deposition affect biocrusts and the ecosystems they inhabit. We integrate experimental and observational data, as well as physiological, community ecology, and biogeochemical perspectives. Taken together, these data highlight the potential for biocrust organisms to respond dramatically to environmental change and show how changes to biocrust community composition translate into effects on ecosystem function (e.g., carbon and nutrient cycling, soil stability, energy balance). Due to the importance of biocrusts in regulating dryland ecosystem processes and the potential for large modifications to biocrust communities, an improved understanding and predictive capacity regarding biocrust responses to environmental change are of scientific and societal relevance.
The importance of biocrusts in the ecology of arid lands across all continents is widely recognized. In spite of this broad distribution, contributions of biocrusts to the global biogeochemical cycles have only recently been considered. While these studies opened a new view on the global role of biocrusts, they also clearly revealed the lack of data for many habitats and of overall standards for measurements and analysis. In order to understand carbon cycling in biocrusts and the progress which has been made during the last 15 years, we offer a multiscale approach covering different climatic regions. We also include a discussion on available measurement techniques at each scale: A microscale section focuses on the individual organism level, including modeling based on the combination of field and lab data. The mesoscale section addresses the CO2 exchange of a complete ecosystem or at the community level. Finally, we consider the contribution of biocrusts at a global scale, giving a general perspective of the most relevant findings regarding the role of biological soil crusts in the global terrestrial carbon cycle.
Biocrusts exert a strong influence on hydrological processes in drylands by modifying numerous soil properties that affect water retention and movement in soils. Yet, their role in these processes is not clearly understood due to the large number of factors that act simultaneously and can mask the biocrust effect. The influence of biocrusts on soil hydrology depends on biocrust intrinsic characteristics such as cover, composition, and external morphology, which differ greatly among climate regimes, but also on external factors as soil type, topography, and vegetation distribution patterns, as well as interactions among these factors. This chapter reviews the most recent literature published on the role of biocrusts in infiltration and runoff, soil moisture, evaporation, and non-rainfall water inputs (fog, dew, water absorption), in an attempt to elucidate the key factors that explain how biocrusts affect land hydrology. In addition to the crust type and site characteristics, recent studies point to the crucial importance of the type of rainfall and the spatial scale at which biocrust effects are analyzed to understand their role in hydrological processes. Future studies need to consider the temporal and spatial scale investigated to obtain more accurate generalizations on the role of biocrusts in land hydrology.
In this paper a novel multivariate method is proposed for the analysis of community response data from designed experiments repeatedly sampled in time. The long-term effects of the insecticide chlorpyrifos on the invertebrate community and the dissolved oxygen (DO)-pH-alkalinity-conductivity syndrome, in outdoor experimental ditches, are used as example data. The new method, which we have named the principal response curve method (PRC), is based on redundancy analysis (RDA), adjusted for overall changes in community response over time, as observed in control test systems. This allows the method to focus on the time-dependent treatment effects. The principal component is plotted against time, yielding a principal response curve of the community for each treatment. The PRC method distills the complexity of time-dependent, community-level effects of pollutants into a graphic form that can be appreciated more readily than the results of other currently available multivariate techniques. The PRC method also enables a quantitative interpretation of effects towards the species level.
The increase in aridity predicted with climate change will have a negative impact on the multiple functions and services (multifunctionality) provided by dryland ecosystems worldwide. In these ecosystems, soil communities dominated by mosses, lichens and cyanobacteria (biocrusts) play a key role in supporting multifunctionality. However, whether biocrusts can buffer the negative impacts of aridity on important biogeochemical processes controlling carbon (C), nitrogen (N), and phosphorus (P) pools and fluxes remains largely unknown.
Here, we conducted an empirical study, using samples from three continents (North America, Europe and Australia), to evaluate how the increase in aridity predicted by climate change will alter the capacity of biocrust‐forming mosses to modulate multiple ecosystem processes related to C, N and P cycles.
Compared with soil surfaces lacking biocrusts, biocrust‐forming mosses enhanced multiple functions related to C, N and P cycling and storage in semiarid and arid, but not in humid and dry‐subhumid, environments. Most importantly, we found that the relative positive effects of biocrust‐forming mosses on multifunctionality compared with bare soil increased with increasing aridity. These results were mediated by plant cover and the positive effects exerted by biocrust‐forming mosses on the abundance of soil bacteria and fungi.
Our findings provide strong evidence that the maintenance of biocrusts is crucial to buffer negative effects of climate change on multifunctionality in global drylands.
The surface layer of soil as transition zone between pedosphere and atmosphere plays a crucial role in exchange processes of nutrients, atmospheric gases and water. Knowledge of its water content is essential, as it governs both physiological and transport mechanisms. In arid and semi‐arid regions, this uppermost soil layer is commonly colonized by biological soil crusts (biocrusts), which play major roles in the global terrestrial carbon and nitrogen cycles. The water status of biocrusts is essential as it controls the activity, productivity and surface exchange of these poikilohydric communities. On‐site analyses of the water content of both bare and crusted soils are thus urgently needed to correctly model the exchange processes of water, nutrients and trace gases at the soil surface.
In this study, we present the biocrust wetness probe ( BWP ), which is the first to reliably measure the water content within biocrusts or the uppermost 5 mm of a substrate. Using a weak alternating current, the electrical conductivity is assessed over time. With an automatic calibration routine, conductivity values are temperature‐corrected and converted into water contents and precipitation equivalents.
During 1 year of continuous field measurements at 5‐min intervals, 60 BWP s worked reliably without any failure. The probes responded immediately and individually upon rain events, showing substrate‐specific water response curves, which are well represented by linear and exponential calibration curves.
The BWP facilitates the spatio‐temporal assessment and interpolation of surface soil wetness and thus biocrust activity, which governs nutrient fluxes, trace gas release and biogeochemical cycles. Its implementation in distributed sensor networks is under development.
Multi-temporal remote sensing information and spectral indices have been extensively used in studies to monitor ecosystem functioning and surface-energy budgets. However, most of these indices did not show good results in areas covered by sparse vegetation, like most of the Drylands. In these ecosystems, open spaces between plants are often covered by biological soil crusts (biocrusts), i.e. communities of cyanobacteria, algae, microfungi, lichens, mosses and other microorganisms growing in the uppermost millimeters of the soil. Due to their mostly dark color, biocrusts influence the spectral response of dryland surfaces, making it necessary to assess the sensibility of widely used spectral indices to variations in biocrusts cover. In this study we used spectra of biocrusts, bare soil and vegetation to analyze the effect of biocrust cover on the spectral response of heterogeneous areas. In a second approach we investigated the impact of biocrust water status on spectral characteristics. Based on spectral mixture analysis, we calculated the response of a wide range of vegetation/biocrust/bare soil landscape compositions, obtaining a total of 702 spectra. These were used to calculate the Normalized Difference Vegetation Index (NDVI), the Enhanced Vegetation Index (EVI), the Water Index (WI) and surface albedo, and the effect of biocrust cover and water status on these indices was analyzed. Biocrusts exerted a considerable effect on vegetation indices and surface albedo, whereas WI was mostly affected by vegetation type and cover. As biocrust cover increased, the value of NDVI and EVI also increased, whereas albedo decreased, and these effects were more important under low vegetation cover. Moreover, as biocrusts almost immediately turned dark after water pulses, the effect of biocrust cover on spectral indices increased already 30 min after wetting. Although these results varied depending on vegetation type, they demonstrate, that biocrusts largely affect the spectral response of dryland surfaces, and they illustrate how this effect is reinforced by water. Thus, biocrusts need to be considered in studies analyzing dryland phenology, productivity and water status. Moreover, in order to increase the accuracy of hydrological and climate forecast predictions, biocrust effects on surface albedo, both in a dry and wet stage, need to be included.
Biological soil crusts (biocrusts) cover up to 60-70% of the soil surface in grasslands rehabilitated since the Grain for Green project was implemented in the hilly Loess Plateau region in 1999, which exerted significant impacts on runoff and soil loss from revegetated grasslands. In the study, field plots were used to investigate runoff and soil loss in sites of a 4- and a 13-year revegetated grassland, with each exhibiting an early and a later successional biocrust, respectively. The objectives of the study were to (1) examine the role of biocrusts on runoff and soil loss during their early and later successional stages in a semiarid region under water erosion, (2) determine the influence of biocrusts on soil antiscourability with different runoff intensities, and (3) isolate the effects of biocrust patches and vascular plant canopies on runoff and soil loss from revegetated grasslands. Treatments used in both sites included (1) retaining biocrusts and plant canopies intact (CP), (2) retaining biocrusts without plant canopies (CNP), (3) retaining plant canopies without biocrusts (PNC), and (4) removing both biocrusts and plant canopies (NCP). The simulated scouring water flux was designed as 7.8, 12.0, and 16.0 L.min(-1) to reflect local rainfall conditions. The results indicated that the runoff yield was increased by biocrust patches in their well-development stage. Runoff was increased by 15.1% when plant canopies were retained and 16.0% when plant canopies were removed in the 13-year revegetated grassland with the 12.0 L.min(-1) scouring water flux. Compared with biocrust patches, plant canopies reduced runoff by 11.3% (with biocrusts) and 8.4% (biocrusts was removed) with the same scouring water flux. No significant difference was found in runoff yield with respect to the four treatments in the 4-year revegetated grassland. In contrast, 92% of the sediments were reduced for the formation of biocrusts in their early successional stage (cyanobacteria-dominated biocrusts) in the 4-year revegetated grassland with respect to CNP compared with NCP at the 12.0 L/min scouring intensity. No sediment was generated on either CP or CNP treatments in grassland revegetated for 13 years (moss-dominated biocrusts) with the same intensity of simulated runoff. Compared with biocrusts, plant canopies had a limited influence on soil loss. This amounted to reductions of 45 and 10% in soil loss for grasslands that revegetated for 4 and 13 years, respectively. The results of the study suggest that biocrusts play an important role in soil loss control from water erosion in semiarid regions, although there was a potential increase in runoff yield. DOI:10.1061/(ASCE)HE.1943-5584.0000633. (C) 2013 American Society of Civil Engineers.
ANOSIM, PERMANOVA, and the Mantel test are all resemblance‐based permutation methods widely used in ecology. Here, we report the results of the first simulation study, to our knowledge, specifically designed to examine the effects of heterogeneity of multivariate dispersions on the rejection rates of these tests and on a classical MANOVA test (Pillai's trace). Increasing differences in dispersion among groups were simulated under scenarios of changing sample sizes, correlation structures, error distributions, numbers of variables, and numbers of groups for balanced and unbalanced one‐way designs. The power of these tests to detect environmental impacts or natural large‐scale biogeographic gradients was also compared empirically under simulations based on parameters derived from real ecological data sets.
Overall, ANOSIM and the Mantel test were very sensitive to heterogeneity in dispersions, with ANOSIM generally being more sensitive than the Mantel test. In contrast, PERMANOVA and Pillai's trace were largely unaffected by heterogeneity for balanced designs. PERMANOVA was also unaffected by differences in correlation structure, unlike Pillai's trace. For unbalanced designs, however, all of the tests were (1) too liberal when the smaller group had greater dispersion and (2) overly conservative when the larger group had greater dispersion, especially ANOSIM and the Mantel test. For simulations based on real ecological data sets, PERMANOVA was generally, but not always, more powerful than the others to detect changes in community structure, and the Mantel test was usually more powerful than ANOSIM. Both the error distributions and the resemblance measure affected results concerning power.
Differences in the underlying construction of these test statistics result in important differences in the nature of the null hypothesis they are testing, their sensitivity to heterogeneity, and their power to detect important changes in ecological communities. For balanced designs, PERMANOVA and PERMDISP can be used to rigorously identify location vs. dispersion effects, respectively, in the space of the chosen resemblance measure. ANOSIM and the Mantel test can be used as more “omnibus” tests, being sensitive to differences in location, dispersion or correlation structure among groups. Unfortunately, none of the tests (PERMANOVA, Mantel, or ANOSIM) behaved reliably for unbalanced designs in the face of heterogeneity.
Climate change will raise temperatures and modify precipitation patterns in drylands worldwide, affecting their structure and functioning. Despite the recognized importance of soil communities dominated by mosses, lichens and cyanobacteria (biocrusts) as a driver of nutrient cycling in drylands, little is known on how biocrusts will modulate the resistance (i.e., the amount of change caused by a disturbance) of the N cycle in response to climate change.
Here, we evaluate how warming (ambient vs. ˜2.5 °C increase), rainfall exclusion (ambient vs. ˜30% reduction in total annual rainfall) and biocrust cover (incipient vs. well‐developed biocrusts) affect multiple variables linked to soil N availability (inorganic and organic N and potential net N mineralization rate) and its resistance to climate change during 4 years in a field experiment. We also evaluate how climate change‐induced modifications in biocrust and microbial communities indirectly affect such resistance.
Biocrusts promoted the resistance of soil N availability regardless of the climatic conditions considered. However, the dynamics of N availability diverged progressively from their original conditions with warming and/or rainfall exclusion, as both treatments enhanced N availability and promoted the dominance of inorganic over organic N. In addition, the increase in fungal:bacterial ratio and the decrease in biocrust cover observed under warming had a negative indirect effect on the resistance of N cycle variables.
Synthesis . Our results indicate that climate change will have negative direct and indirect (i.e. through changes in biocrust and microbial communities) impacts on the resistance of the N cycle in dryland soils. While biocrusts can play an important role slowing down the impacts of climate change on the N cycle due to their positive and continued effects on the resistance of multiple variables from the N cycle, such change will progressively alter N cycling in biocrust‐dominated ecosystems, enhancing both N availability and inorganic N dominance.