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The impact of termites on soil sheeting properties is better explained by environmental factors than by their feeding and building strategies
Abstract
Termites are key soil bioturbators in tropical ecosystems. Apart from mound nests constructed by some advanced lineages, most of the species use their faeces, oral secretions, debris, or soil aggregates to protect themselves from predators and desiccation when they go out to forage. Although this soil ‘sheeting’ is considered to play a key role in soil functioning, the properties of this termite-made material has been poorly studied. The few available data showed that sheeting properties are highly variable with positive, neutral or negative impacts on soil C and clay content, and consequently on soil aggregate stability. Therefore, the objective of this study was to determine the factors controlling the physical (particle size fractions and structural stability) and chemical (pH, electrical conductivity and carbon content) properties of soil sheeting produced by termite species encompassing all feeding and building categories using a dataset representative of an important diversity of biotopes coming from 21 countries from all continents colonized by termites. We showed that sheeting properties were explained by the properties of their environment, and especially by those of the bulk soil (linear relationships), followed in a lesser extent by the mean annual precipitation and biotope. Classic hypotheses related to termite feeding and building strategies were not hold by our analysis. However, the distinction of termites into fungus-growing and non-fungus growing species was useful when differentiating the impact of termites on soil electrical conductivity, C content, and structural stability. The large variability observed suggests the need to redefine termite functional groups based on their impacts on soil properties using a trait-based approach from morphological, anatomical and/or physiological traits.
... Conversely, sheeting made by termites to protect themselves against predators and desiccation (i.e., Harit et al., 2017) while they forage on the ground or on woody materials is very fragile and unstable, leading to a rapid redistribution of minerals and nutrients to the surrounding environment soil. However, their properties are very close to those of the surrounding soil (Harit et al., 2017;Jouquet et al., 2022), and their impact on the cycling of nutrients is considered to be limited. ...
... If termites have a significant impact on soil structure when they build their mound nests (Holt and Lepage, 2000;Abe et al., 2011;Jouquet et al., 2011), their impact is more limited with soil sheeting and totally unknown with graveyard sheeting. A recent meta-analysis showed that soil sheeting built by fungus-growing termites has very similar properties to the surrounding soil (Harit et al., 2017;Jouquet et al., 2022), although it is almost always slightly enriched in clay particles and enriched in C when the soil they use contains less than 2% C. In our study, no difference in soil particle size fractions could be observed between soil types, and only graveyard sheeting was enriched in C org in comparison with the reference soil. ...
... Termites are known to use two main strategies for building soil sheeting (Harit et al., 2017;Jouquet et al., 2022): they either select clay particles and/or incorporate organic matter in the form of saliva. Our findings suggest that workers of Macrotermes natalensis use the second strategy for building protective sheeting, perhaps because they prefer using clay for the construction of their permanent nest structures that host the colony members (see appendix 3). ...
Entombment, or the production of graveyards for the disposal of dead bodies, is not only a practice of human societies but is also observed in nature, including among small invertebrates such as termites. While the influence of termites on soil dynamics has largely been studied in comparing the specific properties of their mounds and protective sheeting with those of the surrounding soil, the properties of their graveyards have never been described before. Using incipient colonies of Macrotermes natalensis reared in a controlled environment, we showed that graveyard sheeting was characterized by a much higher C content in comparison with the reference soil and protective sheeting (4.7-fold increase). As a consequence, a slight increase in the C:N ratio was measured from 8 in the reference soil to 10 in graveyard sheeting. No changes in soil particle size fractions were measured. However, lower Fe and Al contents were measured in sheeting, and micrographs obtained from scanning electron microscopy revealed the presence of calcium carbonate, or calcium oxalate crystals, in sheeting, as well as the presence of organic substances and salt crystals covering termite corpses, most likely for controlling the spread of pathogens. The presence of calcium carbonates and/or calcium oxalate was explained by the very high Ca content within termite bodies. Therefore, this study shows that termite graveyards are likely to constitute unexplored patches of nutrients in soil.
... Therefore, these findings confirm the general assumption that termites' impact on soil texture is preponderant in sandy and poor soils, while it is more limited in more clayey soil (e.g., Jouquet et al., 2015;Bera et al., 2020). In sandy soil, the construction of termitaria usually requires the selection of clay particles, which might come from the deeper soil layers (Abe et al., 2009;Jouquet et al., 2017), and the incorporation of organic matter (C and N), i.e., mostly saliva that fungus-growing termites use for ensuring cohesion between particles (Holt and Lepage, 2000;Jouquet et al., 2022;Zachariah et al., 2017). As observed by others (Bera et al., 2020;Cheik et al., 2018;Jouquet et al., 2015; Subi and Sheela, 2020), a higher soil pH was found in termite constructions in comparison with the surrounding soil in GI. ...
... Examination of the thermograms measuring the fluxes of CO 2 and CO during pyrolysis shows the presence of 2 synchronous peaks between 500 and 525 • C, observed in oxalate-rich samples (see supplementary file 4). These peaks are not observed in CTRL and suggest that high MinC value in TN could correspond to biogenic carbonate, which could be derived from the oxalotrophic activity of termite-associated fungi and bacteria feeding on decaying oxalogenic plant tissues (Cailleau et al., 2011;Mujinya et al., 2011;Suryavanshi et al., 2016;Francis and Poch, 2019;Jouquet et al., 2022). Additionally, these oxalate crystals could also have a bacterial (Hervé et al., 2016) or fungal origin (Hervé et al., 2021). ...
In Cambodia, termite mounds are commonly used by farmers as amendments to increase the fertility of their paddy fields. However, despite their utilization, their chemical and physical properties have not been described yet. Therefore, the aim of this study was to analyze the chemical and physical properties of two termite constructions commonly found in paddy fields: (a) termitaria built and occupied by the fungus-growing termite Macrotermes gilvus and (b) lenticular mounds that are initially built by termites but host a large diversity of other invertebrates and plants. This study shows that these biogenic structures have very specific properties. Termitaria were characterized by higher clay, phosphorus and electrical conductivity than the surrounding soil. However, their effect on carbon dynamics was limited to a modification of the interactions between soil organic matter and minerals and to the presence of carbonates. At the same time, lenticular mounds appeared as patches of nutrients in paddy fields because they were always enriched in carbon, nitrogen, and phosphorus in comparison with the surrounding cultivated soil. Lenticular mounds were also enriched in clay, although this effect was only measured when the sand content in the surrounding environment was >60%. Together with these changes, lenticular mounds were characterized by a lower bulk density, higher saturated hydraulic conductivity (Ksat), and higher water holding capacity. In conclusion, this study shows that termite constructions can be considered fertility and biogeochemical hotspots in paddy fields, thus explaining their use by farmers for improving the fertility of their lands.
... Generally, termite mounds have a higher nutrient concentration (Apori et al. 2020;Lejoly et al. 2019), cation concentration, pH value, and mineral availability in bulk soils (Bera et al. 2020;de Lima et al. 2018) than the surrounding soils; but they show a lower microbial diversity (Aguero et al. 2021). However, these effects vary with termite taxa, ecological groups, and habitat change (Holt, and Lepage 2000;Jouquet et al. 2022). For example, soil-feeding termites affect soil properties primarily through their feces regrowth in clay-organic complexes (Tuma et al. 2022), while fungus-growing termites often rely on symbiosis with the fungi to complete the degradation of the litter and thus alter soil environment (Menichetti et al. 2014). ...
... Van Thuyne and Verrecchia (2021) reviewed that no definitive results can be proposed regarding the effects of termite activity on mound stability. The discrepancies highly depend on termite impacts on mound soil properties (e.g., nutrients, pH, oxides, and cations), among which high organic C (Table S1) or clay content are important agents contributing to nest structural stability (Jouquet et al. 2007(Jouquet et al. , 2018Tuma et al. 2022), rather than their feeding and moundbuilding strategies (Jouquet et al. 2022). Moreover, the reduced aggregate of aboveground mounds may be related to the absence of plant root fragments and mycorrhizal hyphae that are major binding agents for larger soil aggregates (personal observation as Fig. 6). ...
AimsTermites function as “soil engineers” in tropical agroforestry ecosystems. However, of their role in phosphorus (P) cycling little is known. We aimed to investigate the impact of termite activity on soil aggregate stability and P fractions at the aggregate level in a tropical rubber plantation.Methods
Fungus-growing termite mounds (active and abandoned) involving both above- and belowground locations were studied in a 24-year-old rubber stand. The mass percentage and stability of aggregates, P fractions contents and other major chemical properties of soil aggregates were measured. Aggregate-associated P preservation capacity was also calculated.ResultsMore aggregates < 1 mm in size were concentrated in active aboveground mounds than active belowground chambers, thus resulting in weaker stability and erosion resistance, whereas the opposite trend occurred in abandoned mounds. The concentrations of labile P (in > 2 mm aggregate size), moderately labile P (0.25–1 mm), and non-labile P (0.053–1 mm) in active aboveground mounds were significantly higher than other types. The changes in specific P forms enriched TPi in aggregates > 2 mm and TPo in 0.053–1 mm size of active aboveground mounds relative to others, implying the importance of Po storage in microaggregates induced by termite activity involved in long-term P transformation. Furthermore, middle-sized (0.25–2 mm) aggregates stored more P and represented the highest P storing capacity, especially for active belowground chambers.Conclusions
These results suggest that in the presence of termite activity, P cycling is greatly enhanced in aboveground mounds despite the poor aggregate stability, whereas P forms are stable after mound abandonment, except for a higher H2O-Pi concentration aboveground. Our study provides an important reason why mound soils can be considered as fertility amendments for agroforestry practices in P-deficient tropical soils.
... Thus, the high diversity of species in soil prompted initial proposals for grouping soil biodiversity (Swift et al., 1979), which continue to be applied today (Barrios, 2007;Guilland et al., 2018). These proposals consider: i) microflora 1-100 μm (Fierer and Jackson, 2006;Ibekwe et al., 2002;Nielsen et al., 2002); ii) microfauna 5-120 μm (González et al., 2001); iii) mesofauna 80 μm-2 mm (Römbke et al., 2005;Ruf, 1998;Da Silva Souza et al., 2014), and iv) macrofauna 500 μm-50 mm (Jouquet et al., 2022;Pérès et al., 1998;Römbke et al., 2005). However, along with this grouping, other proposals have also integrated the relationships between soil organisms and microorganisms with ecosystem functions. ...
Biological indicators of soil quality express the capacity of a soil to maintain its ecosystem functions and services between socio-ecosystem inflection thresholds; therefore, they are determinants in management and land use decisions. However, their development until a few decades ago was limited for several reasons: reductionism and early development of other dimensions, such as physical and chemical indicators or their methodological complexity, thus affecting the importance given to biological factors and the integral evaluation of soil quality or health. Thus, this review presents a mapping of the scientific contributions of the last 50 years oriented to the theoretical and methodological development of biological indicators of soil quality, identifying their development and application in these decades. We conducted a bibliometric analysis that allowed us to present an overview of the field with respect to scientific production: temporality, geographical origin, institutional origin, journals that promote the development of the field, articles with greater influence by citation in the field of study, and the co-occurrences of these indicators in research. This analysis was complemented at the second stage by a systematic review of the literature with the greatest impact by citation. We found 2320 scientific papers distributed mainly in the United States (17.8%), China (12.2%), Brazil (8.3%), India (6.3%), and European Mediterranean countries, such as Spain, France, and Italy (14.2%). Our review showed 25 biological indicators with the highest occurrence; for example, microbial biomass (1 1 8), enzymatic activity (90), and organic matter (78); other indicators, such as earthworms, nematodes, or springtails, are also reported. All indicators showed relationships, to a greater or lesser extent, with soil biodiversity and its functions in the landscape. Important advances in soil indicators have developed gradually in the last few decades, with scientific efforts mainly concentrated in developed and emerging countries. In the last decade, the production curve continues with a growth trend., and research questions in the field revolve around the linkage of diversity and function from a molecular point of view. The scope goes beyond productivity, manifesting the real need to conserve and manage the ecosystem services of a limited and non-renewable natural resource. Pioneering research should begin to report on the scope of soil biological monitoring and its influence on policy, management, and land use. Finally, the promotion of research networks with developing countries can foster the development of regional and local soil monitoring policies in these regions
Understanding how soil fauna impact soil aggregate dynamics remains a critical issue in soil science, especially because of the influence on soil aggregate stability on key ecological and environmental processes. This question is even more crucial in tropical countries, where soils are particularly vulnerable to erosion. In many tropical environments, soil bioturbation is mostly carried out by termites. Based on their different building strategies, termites are usually differentiated into two functional groups: the fungus growing (FG) and non-fungus growing termites (non-FG). In this study, we focused on the properties of soil sheeting, i.e., small sized soil aggregates that are built on the ground or on plant materials by termites. Using partial least squares structural equation modeling (PLS-SEM), we showed that the stability of non-FG sheeting was associated with the properties of the surrounding soil, thus suggesting (i) a low ability or need of termites to adapt the stability of their sheeting to their biotic and abiotic environments, (ii) a rapid turnover of the organic matter incorporated by non-FG, which is only superficially incorporated into soil aggregates. The sheeting of FG termites was generally enriched in clay and impoverished in carbon. However, despite changes in soil properties, PLS-SEM did not satisfactorily account for sheeting stability (i.e., no direct or indirect path correlations between the stability of soil sheeting and the other measured variables). Therefore, this study suggested a reorganization of soil aggregates and an adaptation of sheeting properties to the environment with a positive impact of termites on soil sheeting stability restricted to semi-arid to arid environments (mean annual precipitation <500 mm year⁻¹), in agro-ecological biotopes, and when sheeting covered leaves in comparison to wood. Hence building strategies between FG and non-FG termites can have functional consequences in terms of soil aggregate stability in tropical soils.
Enhancing biodiversity in cropping systems is suggested to promote ecosystem services, thereby reducing dependency on agronomic inputs while maintaining high crop yields. We assess the impact of several diversification practices in cropping systems on above- and belowground biodiversity and ecosystem services by reviewing 98 meta-analyses and performing a second-order meta-analysis based on 5160 original studies comprising 41,946 comparisons between diversified and simplified practices. Overall, diversification enhances biodiversity, pollination, pest control, nutrient cycling, soil fertility, and water regulation without compromising crop yields. Practices targeting aboveground biodiversity boosted pest control and water regulation, while those targeting belowground biodiversity enhanced nutrient cycling, soil fertility, and water regulation. Most often, diversification practices resulted in win-win support of services and crop yields. Variability in responses and occurrence of trade-offs highlight the context dependency of outcomes. Widespread adoption of diversification practices shows promise to contribute to biodiversity conservation and food security from local to global scales.
Formosan subterranean termites, Coptotermes formosanus Shiraki, usually transport clay materials into tree hollows and bait stations. Our previous research showed that C. formosanus preferred to aggregate in the locations containing field-collected clay samples, but it was not clear whether this preference was influenced by clay types and/or moisture. In the present study, we conducted multiple-choice tests under low-moisture (25% moisture) or moderate-moisture (50% moisture) conditions to evaluate the aggregation and wood-feeding preferences of C. formosanus responding to hollow wooden cylinders (simulation of tree hollows) or baiting containers (simulation of bait stations) filled with different clay materials (bentonite , kaolin, chlorite, illite, or attapulgite), soil, or unfilled. Under low-moisture conditions, the majority of termites were found in the wooden cylinders or baiting containers filled with bentonite. Under moderate-moisture conditions, however, termites preferred to aggregate in wooden cylinders filled with chlorite or attapulgite; the percentages of termites that stayed in baiting containers filled with chlorite, attapulgite or soil were similar, which were significantly higher than those that filled with kaolin, illite, or unfilled. We then conducted no-choice tests to study the effect of clay materials on termites. Under low-moisture conditions, clay filled in the baiting containers significantly increased survivorship and body water percentage (an indicator of termite vigor) of termites, whereas no similar effect was detected under moderate-moisture conditions. This study demonstrated that both clay type and moisture affect termites' preference.
Seven earthworm ecological categories, including anecics, endogeics and epigeics, were defined by Marcel Bouché in 1972 based only on morpho-anatomical characteristics measured on European lumbricids. These categories had an outstanding success, and their use was generalized even outside of Europe. However, most of the time, only the three main categories are used, and over two decades, these categories have been considered functional groups, i.e. to presume how earthworms influence the soil functioning. Moreover, this relationship between ecological categories and functional groups is seldom tested and often uncritically accepted by soil biology researchers. It is then not surprising to observe unexpected trends when earthworm species are gathered in ecological categories to, for instance, analyze burrow systems or cast properties. We believe it is time to acknowledge that ecological categories are not functional, because they were not made for this purpose. We also propose three future directions in order to either improve our knowledge on the functional effects of earthworms or to build new authentically functional groups: (i) going back to the seven initial ecological categories to provide greater accuracy than the usage of the simplified three-level classification; (ii) testing, for a set of selected species, the functionality of the groups, being ecological categories or new tailored ones; and (iii) using trait-based approach in order to study the correlation between some earthworm traits and main soil functions.
Soil aggregation and its effects on soil C storage have been addressed in thousands of research articles over the last 40 years. Research has been mostly focused on the resistance of aggregates to mechanical disruption and the role of organic matter in aggregate stabilization. On the other hand, relatively little attention has been paid to identifying the microbial, plant root and macro-invertebrate actors and physical processes that continuously create and destroy aggregates. The sum and dynamics of these processes determines the ability of soils to store and conserve C. Understanding the interactions between aggregation dynamics and C transformations in soils therefore requires a precise identification of the agents that produce aggregates and knowledge of the rates of formation and persistence in the pools thus identified.
We propose to separate macro-aggregated components of different, physicogenic and biogenic origins from non-macro-aggregated soil on a morphological basis, using a simple visual technique. The specific biological or physico-chemical agent which produced each individual macro-aggregate can then be determined using Near Infrared Spectroscopy (NIRS). A general description of the distribution and quality of organic matter among the different groups of macro-aggregates can be made. Simple soil re-aggregation or dis-aggregation tests conducted in field conditions further measure the production of different macro-aggregates with time and their mean residence times in the studied soil. Respirometry measurements on each recognized category of macro-aggregates evaluate the respective C losses through respiration. The methods described here will allow the dominant pathways of C flow at a given site to be characterized and possible management options to increase C storage identified. We finally discuss the different assumptions made to build this simple model and offer ways to test the methodology under field conditions.
Soils are home to more than 25% of the earth’s total biodiversity and supports life on land and water, nutrient cycling and retention, food production, pollution remediation, and climate regulation. Accumulating evidence demonstrates that multiple sustainability goals can be simultaneously addressed when soil biota are put at the center of land management assessments; this is because the activity and interactions of soil organisms are intimately tied to multiple processes that ecosystems and society rely on. With soil biodiversity at the center of multiple globally relevant sustainability programs, we will be able to more efficiently and holistically achieve the Sustainable Development Goals and Aichi Biodiversity Targets. Here we review scenarios where soil biota can clearly support global sustainability targets, global changes and pressures that threaten soil biodiversity, and actions to conserve soil biodiversity and advance sustainability goals. This synthesis shows how the latest empirical evidence from soil biological research can shape tangible actions around the world for a sustainable future.
Termites are one of the key ecosystem engineers in tropical forests where they play a major role in decomposition rates, both above and belowground. The interest in termite ecology and biogeography has increased in the last few decades; however, the lack of comparable data has limited the wider impact of termite research. For Ecuador, termite studies are relatively rare and comparable data that are collected using standardized sampling methods are missing. In this study, we aim to 1) provide comparable data of termite species and feeding-group diversity from two primary forests in Ecuador and 2) explore the differences in termite species and feeding-group diversity between the two forest sites. Sampling took place in the national parks of Yasuní and Podocarpus where three belt transects (100 × 2 m) following Jones and Eggleton (2000) were conducted in each forest. We found that termite species richness was higher in Yasuní (56 species) than in Podocarpus (24 species) and that 57% of the sampled termite genera had never previously been recorded in Ecuador. The inter-site species dissimilarity was almost complete (Bray Curtis (±SD), 0.91 ± 0.01), which may have been linked to the difference in tree density and species richness in the two forests. Termite feeding-groups diversity was significantly higher in Yasuní than in Podocarpus with the exception of soil-feeding termites which may have been due to competition between humus-and soil-feeding species.
Disturbance, particularly agricultural expansion is one of the major threats to the biodiversity and ecological functions of tropical and sub-tropical ecosystems. In this regard, we examined changes in the species richness, abundance, and diversity of termites across different disturbance treatments in a sub-tropical semi-arid savanna in south eastern Zimbabwe. Nine transects (100 × 2 m) representing three habitat disturbance treatments (primary woodland; grazing area; agricultural field) were sampled for termites using a rapid biodiversity assessment protocol. Termites were more abundant and species-rich in primary woodland and grazing area than in the agricultural field. Twelve termite species from three sub-families were present, with Microtermes sp. constituting 35% of the identified termite species. Termite feeding group structure differed significantly among land-use types, and of all termites present, wood-feeding termites were the most abundant while soil-feeders were rare in the agricultural field. In conclusion the observed pattern in termite species richness and relative abundance indicates that termites are very resilient to natural disturbance and might actually benefit from some natural disturbances like they did in the grazing area of this study, but they are not resilient to extreme anthropogenic disturbance. Although there was no notable difference in termite species richness and relative abundance between agricultural field and primary woodland, the pattern observed across the three sites may be potential support for the IDH suggesting that intermediate levels of physical disturbance intensity influence the structure and functioning of termite assemblages in semi-arid savanna.
Termites are considered soil engineers and key bioturbators in tropical and subtropical soils. A large number of studies have described the specific properties of the aboveground mounds that termites construct to protect their colonies from environmental hazards. However, there is a paucity of information on properties of soil sheetings; more temporary but often extensive structures are covering over or inserted within substrates on the ground such as leaves and woody materials or components of arboreal runways. Such sheetings are conspicuously produced not only by the Macrotermitinae but also by many other unrelated taxa. Here, we review the available literature and discuss (i) the relationship between rainfall and soil sheeting production and (ii) how termites affect the clay and C contents in soil sheetings. This reveals that sheeting production is highly variable and site specific. We also found that soil sheetings are always enriched in clay, but their impacts on soil C content are variable and related to the C content of the parent soil and to the quality of the substrates consumed by termites.
Termites are undoubtedly key soil organisms in tropical and subtropical soils. They are soil engineers in influencing the physical, chemical, and biological properties of soils and, consequently, water dynamics in tropical and subtropical ecosystems. To appreciate the effect of termites on soil, there is a need for a thorough understanding of the ecological needs and building strategies of termites and the mechanisms regulating termite diversity at local and regional scales. Termite impacts on soil properties and water dynamics can be differentiated at four different scales: (i) at the landscape scale, where termites act as heterogeneity drivers; (ii) at the soil profile scale, where termites act as soil bioturbators; (iii) at the aggregate scale, where they act as aggregate reorganizers; (iv) and last, at the clay mineral scale, where they can act as weathering agents. Last, we discuss recent literature on termite engineering published in the last 10 years in the major journals of soil science and suggest new research topics that could contribute to improved knowledge of the impact of termites on soil properties and water dynamics.
Many termite species use clay to build foraging galleries and mound-nests. In some cases clay is placed within excavations of their wooden food, such as living trees or timber in buildings; however the purpose for this clay is unclear. We tested the hypotheses that termites can identify load bearing wood, and that they use clay to provide mechanical support of the load and thus allow them to eat the wood. In field and laboratory experiments, we show that the lower termite Coptotermes acinaciformis, the most basal species to build a mound-nest, can distinguish unloaded from loaded wood, and use clay differently when eating each type. The termites target unloaded wood preferentially, and use thin clay sheeting to camouflage themselves while eating the unloaded wood. The termites attack loaded wood secondarily, and build thick, load-bearing clay walls when they do. The termites add clay and build thicker walls as the load-bearing wood is consumed. The use of clay to support wood under load unlocks otherwise unavailable food resources. This behaviour may represent an evolutionary step from foraging behaviour to nest building in lower termites.
Fungus-growing termites are involved in many ecological processes and play a central role in influencing soil dynamics in the tropics. The physical and chemical properties of their nest structures have been largely described; however less information is available concerning the relatively temporary structures made above-ground to access food items and protect the foraging space (the soil 'sheetings'). This study investigated whether the soil physical and chemical properties of these constructions are constant or if they vary depending on the type of food they cover. Soil samples and soil sheetings were collected in a forest in India, from leaves on the ground (LEAF), fallen branches (WOOD), and vertical soil sheetings covering the bark of trees (TREE). In this environment, termite diversity was dominated by Odontotermes species, and especially Odontotermes feae and Odontotermes obesus. However, there was no clear niche differentiation and, for example, O. feae termites were found on all the materials. Compared with the putative parent soil (control), TREE sheetings showed the greatest (and most significant) differences (higher clay content and smaller clay particle sizes, lower C and N content and smaller d 13 C and d 15 N), while LEAF sheetings were the least modified, though still significantly different than the control soil. We suggest that the termite diversity is a less important driver of potential soil modification than sheeting diversity. Further, there is evidence that construction properties are adapted to their prospective lifespan , with relatively long-lasting structures being most different from the parent soil.
Rapid disappearance of crop residue used as soil surface cover in conservation tillage systems reduces the envisaged soil cover benefits. This study was conducted in a conservation tillage experiment, established in 2003 in Nyabeda, western Kenya,to (1) characterize crop residue disappearance during crop growth, and (2) assess termite activity and characteristics of soil (carbon concentration and aggregate stability) in termite-molded sheetings and mound soil. Loss of surface-placed residue in the presence of macrofauna (defined as >1mm) was up to 83% in 3.5 months, compared to 33% in the absence of macrofauna. Overall, residue loss was up to 34% higher for buried than surface-placed residue. Termite sheetings had, depending on the cropping system, 11- 26% and 25- 42% higher (P<0.01) carbon than bulk soil (0-5 cm depth) and termite mound soil, respectively. Mound soil had 68% of the soil as water stable macroaggregates (i.e., >250 µm) compared to 57% and 53% for bulk soil and termite sheetings, respectively. Also, large and small macroaggregates were elevated under conservation tillage compared to conventional tillage for continuous maize and maize-soybean rotation systems. We conclude that termites can affect soil carbon and its distribution considerably through their sheetings and strategies to supplement residue under ‘sustained attack” by soil fauna are needed if a specific soil cover rate is to be maintained in conservation tillage.
Heterotermes aureus and Gnathamitermes perplexus are dominant factors in soil turnover, litter decomposition and nutrient cycling in the Sonoran Desert. Together they move c744 kg/ha of soil to the surface each year. They increase the clay content of surface soils by 21 kg/ha/yr by selectively bringing up soil richer in clay. They alter the pH from slightly acidic to basic, mainly by bringing lime to the surface. They enrich the soil with organic C, total N, Ca, Mg, K and Na as a result of digesting plant material and depositing feces and/or saliva in their workings at the surface. Both are general feeders, but their characteristic attacks on different sets of preferred litter components tend to be complementary. Nutrients released by Heterotermes may remain in its workings for months or years, while those of Gnathamitermes are released within weeks or months by the first heavy rains. -Authors
Bioindicators, as taxa or functional groups, are widely used as indicators of environmental change, specific ecological factors or taxonomic diversity. The use of ecological, environmental and biodiversity indicators, is reviewed here. Although indicator taxa are considered to be generally unreliable as broad indicators of biodiversity, they may serve a useful function in identifying ecological characteristics or monitoring the effects of habitat management. Use of only a narrow range of taxa may be unreliable, and is particularly vulnerable to distortion by a small number of invasive species. Taxa also need to be selected to reflect the specific ecosystem being studied. It is recommended that isopods be used for soil systems (if there is sufficient local diversity), in some areas earthworms or mites may be useable but are generally too difficult to identify to be practically useful. In the ground layer indicator sets could include ants, millipedes, molluscs (snails in particular), ground beetles, harvestmen and gnaphosid spiders. Foliage-inhabiting indicators could comprise ants, chrysomelid leaf beetles, theridiid spiders and arctiid moths. Ants, orthopterans and butterflies may be appropriate for use in open habitats. These basic sets should be supplemented by other taxa where appropriate resources and taxonomic expertise are available.
Termites play important roles in organic matter decomposition, nutrient cycling, and soil structure in tropical rain forests. When forests are replaced by agriculture, termite species richness, abundance, and function often decline. We compared the termite assemblage of a primary forest site with that of a low plant diversity, palm-based agroforest (five plant species) and a high plant diversity, home-garden agroforest (10 plant species) using a rapid biodiversity assessment protocol. In comparing the primary forest termite species composition to previously published studies, we found soil feeders and the Apicotermitinae to be more dominant than previously reported in Amazonia. Thirty percent of the species belonged to the Apicotermitinae, and an unusually high percentage (57%) of species were soil feeders. Unexpectedly, the palm-based agroforest, despite its lower plant diversity, was closer to primary forest in termite species composition, rate of species accumulation, and proportions of species in taxonomic and functional classes than was the home-garden agroforest. This suggests that particular plant attributes may better determine the termite assemblage than plant diversity alone in these agroecosystems. Unlike other agroecosystems reported in the literature, Apicotermitinae and soil feeders were proportionally more abundant in these agroforests than in primary forest. The ability of agroforests to support populations of soil feeders has a potentially positive effect on soil fertility in these agroecosystems; insomuch as feeding guild is a proxy for function, these closed-canopy agroforests may be able to sustain the same termite-mediated functions as primary forest.
In previous studies, we have shown that fungal communities in soil are quantitatively and qualitatively modified when termite sheetings are constructed, but the reasons for these changes are unknown. In this work we described the succession of fungal communities in the sheetings of three fungus-growing termite species by combining cultivation techniques and culture-independent methods specially DNA extraction, PCR and denaturing gradient gel electrophoresis (DGGE). We also estimated the abundance of fungi by using plate-count technique. The fungal communities of these sheetings were sampled at different ages. The potential functions of fungal communities was assessed by their capabilities of degrading different substrates including proteins, polysaccharides and tannins. Significant differences were found between the fungal communities of termite sheetings and those of surrounding soil. These differences were observed at quantitative, qualitative and functional level as well and were marked particularly in the fresh sheetings of termites. The characteristics of fungal communities of the surrounding soil were quite similar with those observed in the old sheetings of termites. These results show that the fungal communities are modified at once in freshly built sheetings, rather than by a progressive succession, as had been expected.
The aim of this study was to search for specific signatures of biogenic structures (i.e. earthworm casts, termite sheathings and mound material, and ant deposits) made by 15 species of soil engineers in a Colombian savanna. We thus investigated the organic matter (OM) biochemical composition of biostructures using near infrared spectroscopy (NIRS) and its relationship with selected biological (respirometry) and chemical attributes.
We found significant differences in OM quality and potential respiration rate among biostructures. These results were attributed to production patterns of biostructures and invertebrate feeding behaviour. A multiple co‐inertia analysis was performed with NIRS, respirometry and chemical results. It separated (i) carton termite mounds, (ii) earthworm casts and organo‐mineral termite mounds and (iii) termite sheathings and ant deposits.
These results suggest that NIRS spectra might be used as ‘fingerprints’ to identify organisms responsible for soil aggregate production. Moreover, the ordination given by the co‐inertia analysis is proposed as a basis for a functional classification of soil engineers, assuming that different biostructure properties imply different effects on soil functioning.
Earthworms are usually assumed to enhance plant growth through different mechanisms which are now clearly identified. It is however difficult to determine their relative importance, and to predict a priori the strength and direction of the effects of a given earthworm species on a given plant. Soil properties are likely to be very influential in determining plant responses to earthworm activities. They are likely to change the relative strength of the various mechanisms involved in plant-earthworm interactions. In this paper, we review the different rationales used to explain changes in earthworm effect due to soil type. Then, we systematically discuss the effect of main soil characteristics (soil texture, OM, and nutrient contents) on the different mechanisms allowing earthworm to influence plant growth. Finally, we identify the main shortcomings in our knowledge and point out the new experimental and meta-analytical approaches that need to be developed. An example of such a meta-analysis is given and means to go further are suggested. The result highlights a strong positive effect size in sandy soil and a weakly negative effect in clayey soil.
1. Gut content analysis of termites was undertaken using microscopical techniques. The 46 study species covered the entire range of taxonomic and feeding forms within the Order.
2. Inter-specific gut contents data were analysed using principal components analysis, placing species along a clear humification gradient based on variations in the amount of silica and plant tissue fragments in the gut.
3. Redundancy analysis was used to find morphological correlates of the observed variation in gut contents. A total of 22 morphological characters (out of 45 candidate characters) were correlated significantly with the gut contents.
4. Three of the 22 significantly correlated characters unambiguously defined feeding groups, which were designated groups I to IV in increasing order of humification of the feeding substrate. Group I contains lower termite dead wood and grass-feeders; group II contains Termitidae with a range of feeding habits including dead wood, grass, leaf litter, and micro-epiphytes; group III contains Termitidae feeding in the organic rich upper layers of the soil; group IV contains the true soil-feeders (again all Termitidae), ingesting apparently mineral soil. These groupings were generally supported statistically in a canonical covariance analysis, although group II apparently represents termite species with a rather wide range of feeding habits.
5. Using existing hypotheses of termite phylogenetic relationships, it seems probable that group I feeders are phylogenetically basal, and that the other groupings have arisen independently on a number of occasions. Soil-feeding (i.e. group III and group IV feeding) may have evolved due to the co-option of faecal material as a fungal substrate by Macrotermitinae-like ancestral forms. As a consequence, these forms would have been constrained to build nest structures from soil and would therefore have passed at least some soil through their guts.
Through their role as 'ecosystem engineers', termites provide a range of ecosystem services including decomposition, and carbon and nitrogen cycling. Although termite diversity levels differ between regions as a result of variation in regional species pool size, in general, termite diversity is thought to decline with elevation. This study (1) investigated how termite species density, abundance, functional group diversity and termite attack on dead wood vary with altitude along an Amazon-Andes altitudinal gradient in Peru; (2) identified likely environmental causes of this pattern; and (3) explored the implications of termite presence for ecosystem functioning (notably for decomposition). Termites were sampled with a standardized 100 × 2 m straight-belt transect at five undisturbed forest sites along a gradient 190 to 3025 m, as were environmental variables and termite and fungus attack on dead wood. Termite diversity was similar to that found at comparable sites in South America, and there was little turnover of assemblage composition with elevation suggesting that montane specialists are not present. Termite diversity declined with increased elevation, though the upper distribution limit for termites was at a lower elevation than anticipated. We suggest that key drivers of this elevation pattern are reduced temperature with altitude and mid-elevation peaks in soil water content. Also, attack on dead wood diminished with decreasing termite indirect absolute abundance, while the depth of the soil humic layer increased. We hypothesize that termite abundance is a major accelerant of decomposition rates (and associated mineralization) in Amazonian forests. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp. © 2010 The Author(s). Journal compilation © 2010 by The Association for Tropical Biology and Conservation.
1. Termites are major decomposers in tropical regions and play an important role in soil processes. This study measured the impact of land‐use intensification on the termite assemblage of lowland rain forest in Jambi Province, on the Indonesian island of Sumatra. Termite composition was assessed in seven land‐use types along a disturbance gradient, from primary forest, through different silvicultural systems, to grassland and cultivated land without trees. A range of environmental variables was also measured.
2. Termite species richness and relative abundance declined as follows: primary forest > selectively logged forest > mature ‘jungle rubber’ (a diverse agro‐forest dominated by rubber trees) > mature rubber plantation > young Paraserianthes falcataria plantation (a softwood tree) > Imperata cylindrica grassland > cassava garden. Termite richness fell from 34 species in the primary forest to one species in the cassava garden. The relative abundance of soil‐feeding termites showed a significantly greater decline along the gradient than did wood‐feeding termites.
3. Of the environmental variables, woody plant basal area was most strongly correlated with termite species richness ( r = 0·973) and relative abundance ( r = 0·980). This reflects the response of forest‐adapted termites to progressive simplification of the physical structure of the habitat, resulting in the reduction of canopy cover and alteration in microclimate, and the loss of feeding and nesting sites.
4. Synthesis and applications . Comparisons with other studies show that the decline in termite species richness and relative abundance seen at Jambi is a general trend that occurs elsewhere when forests are converted to other land uses. To help mitigate the loss of termites when forests are disturbed, we recommend the following management practices: the use of reduced‐impact logging techniques, maximizing forest patch size and connectivity, minimizing length of forest edges, and leaving dead wood to decay in situ .
In the early 70s, the soil biologist Marcel Bouché classified French earthworms species into defined ecological categories. This classification system was immensely successful and is still widely used to describe earthworm functional groups even outside of Europe. Bouché used morpho-anatomical traits to differentiate three main categories: epigeic, anecic and endogeic. However, the way species are assigned to a category was not explicitly described in Bouché’s work. Thus, some earthworm species can still be assigned to two categories depending on the way researchers interpret Bouché’s description. To solve these issues and avoid unnecessary controversies, we applied PCA and random forest models to the seminal data of Marcel Bouché (earthworm morpho-anatomical traits). Their assignment to Bouché’s three main categories allowed us to statistically redefine the different categories and determine which traits are the most influential. We found that the three main traits were skin pigmentation (from none to black), body length (mean of the minimal and maximal values) and skin coloration (yes or no), followed by 10 other morphological and anatomical traits. We then used this approach to assign a likely category to all of the species studied by Bouché, resulting in a new triangular graph including other categories such as epi-anecic, endo-anecic, epi-endogeic and intermediate. Finally, we calculated the percentage that each species belongs to each main ecological category. This represents a paradigm shift and may change our vision of earthworm communities enabling the computation of the percentage of anecic, endogeic and epigeic species at the community level and thus overcoming the limits and debate about fixed ecological categories for each species.
Soil organic matter (SOM) dynamics and termite activity have now been widely accepted as key players for improving soil properties in tropical agro-ecosystems. Numerous studies have described environmental impacts of aboveground termite mounds, while few data are available on temporary structures built for food foraging, called termite sheetings. The effects of termite activity on soil properties resulting from organic matter (OM) amendment under two contrasting management practices were studied in similar pedological and climatic conditions in Southern India (Auroville). Our results showed an increase in bio-available nutrients (K, Mg and P), organic carbon (OC) content, cationic exchange capacity (CEC), exchangeable base cations and water pH in the termite sheetings compared to the underlying and reference soils, in the organic tilled field. On the other hand, only bio-available K increased in the permanent raised beds. Aggregation processes were improved in termite sheetings for the organic tilled field, as the amounts of macroaggregates (250 μm – 2 mm) and protected microaggregates increased, whereas the amount of free microaggregates (50–250 μm) decreased. Moreover, termite activity favoured SOM storage in termite sheetings by increasing OC content in each aggregate fraction, while no differences were observed in the permanent raised beds. Our study demonstrates that termite activity can improve nutrient availability, carbon storage and pH conditions in agro-ecosystems but that the magnitude of the effect likely depends on the agronomic practices in use.
It has long been established that earthworms beneficially affect plant growth. This is to a large extent due to the high fertility of their casts. However, it is not clear how fertile casts are compared to bulk soil, and how their fertility varies between earthworm feeding guilds and with physico-chemical soil properties. Using meta-analysis, we quantified the fertility of earthworm casts and identified its controlling factors. Our analysis included 405 observations from 81 articles, originating from all continents except Antarctica. We quantified cast fertility by determining the enrichment of earthworm casts relative to the bulk soil (“relative cast fertility”; RCF) for total organic carbon (TOC), total phosphorus (P) and total nitrogen (N) concentrations, as well as for plant available pools of N (total mineral N) and P (available P: P-Olsen, P-Bray or comparable metrics), C-to-N ratio and microbial biomass C. In addition to these response variables, we studied four additional ones closely related to soil fertility: pH-H2O, clay content, cation exchange capacity (CEC), and base saturation. With the exception of C-to-N ratio, microbial C and clay content, all studied response variables were significantly increased in casts compared to the bulk soil. Increases in total elemental concentrations (TOC, total P and total N), which are the result of preferential feeding or concentration processes, were comparable and ranged between 40 and 48%. Nutrient availability, which is to a large extent the result of (bio)chemical transformation processes in the earthworm gut, was increased more strongly than total elemental concentrations (241% and 84% for mineral N and available P, respectively). Increases in pH (0.5 pH units), cation exchange capacity (40%), and base saturation (27%) were also large and significant. None of the soil-related possible controlling factors could satisfactorily explain the variation in RCF; plant presence (or other sources of organic C input such as residue application) was the only controlling factor that consistently increased RCF across soil properties. With the exception of available P, none of the studied response variables could be linked to earthworm feeding guild. Our results show that earthworm casts are much more fertile than bulk soil for almost all analysed cast fertility properties. However, these positive RCFs are to a large extent dependent upon the presence of plants. In general, earthworm feeding guild or specific physico-chemical soil properties could not explain the large variability in RCF for the various response variables. Therefore, we hypothesize that RCF effects depend on intricate interactions between earthworm species traits and specific soil properties. Understanding these interactions requires trait-based approaches combined with mechanistic modelling of biochemical processes in the earthworm gut and casts.
Animal constructions such as termite mounds have received scrutiny by architects, structural engineers, soil scientists and behavioural ecologists but their basic building blocks remain uncharacterized and the criteria used for material selection unexplored. By conducting controlled experiments on Odontotermes obesus termites, we characterize the building blocks of termite mounds and determine the key elements de ning material choice and usage by these accomplished engineers. Using biocement
and a self-organized process, termites fabricate, transport and assemble spherical unitary structures called boluses that have a bimodal size distribution, achieving an optimal packing solution for mound construction. Granular, hydrophilic, osmotically inactive, non-hygroscopic materials with surface roughness, rigidity and containing organic matter are the easiest to handle and are crucial determinants of mass transfer during mound construction. We suggest that these properties, along with optimal moisture availability, are important predictors of the global geographic distribution of termites.
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The present study provides evidence of the effectiveness of some termite species in restoring barren soil and in maintaining long-term soil productivity, thereby facilitating sustainable agriculture in sub-Saharan West Africa. Fungus-growers, in particular, move large quantities of soil to cover their food sources with ‘soil sheetings’, which protect the termites during foraging. We selected study sites in northern Burkina Faso from four age-stages of the traditional restoration system Zaï, thus spanning three decades of soil restoration—barren, crusted land, a millet field, and two reforested sites. In a randomized block design, termites were attracted to different organic materials. The aim was to assess the impact oftheir foraging structures (soil sheetings, foraging holes) on the restoration progress. We quantified soil turnover by termites, macroporosity, water infiltration rate, and physicochemical soil properties. Fungus-growing Odontotermes and Macrotermes species were the decisive soil engineers throughout the year, but only Odontotermes initiated the restoration process. The dry weight of soil bioturbated during the dry season ranged between 216 and 32 tons ha-1mon-1 in the most rehabilitated Zaï forest and the barren area, respectively. By creating tunnels, the foraging activity of termites increased the water infiltration rate by a factor of 2 to 4. Sheetings built on compost and hay showed significant increase in most parameters relevant for plant growth, especially during the dry season. However, the benefits resulting from the termites’ tunnelling activities (improved water availability and soil aeration via macropores, soil turnover) are in the early stages of Zaï restoration likely to be more essential than the increased nutrient contents in sheeting soil, since water deficit leads to sapling mortality much faster than nutrient shortage. Our study revealed that the impact of termites is dependent on the particular species and their ecological requirements. Further studies in other areas are urgently required to clarify how generally valid our results are.
Soil organisms are an integral component of ecosystems, but their activities receive little recognition in agricultural management strategies. Here we synthesize the potential of soil organisms to enhance ecosystem service delivery and demonstrate that soil biodiversity promotes multiple ecosystem functions simultaneously (i.e., ecosystem multifunctionality). We apply the concept of ecological intensification to soils and we develop strategies for targeted exploitation of soil biological traits. We compile promising approaches to enhance agricultural sustainability through the promotion of soil biodiversity and targeted management of soil community composition. We present soil ecological engineering as a concept to generate human land-use systems, which can serve immediate human needs while minimizing environmental impacts.
This chapter reviews the advances made in our knowledge of the effects of termites on the physical, chemical and biological properties of soils. Emphasis has been placed on more recent contributions, particularly those that explore new concepts in the ecology of termites and soils. There are sections dealing with the effects of termite activity on soil profile development, soil physical properties, soil chemical properties, soil microbiology and plant growth. The physical effects of termites on soils range from micromorphological to soil profile evolution and structure. Recent evidence points to the substantial positive influence of termites on soil hydraulic conductivity and infiltration rates. Their influence on organic matter decomposition and nutrient recycling rates are well recognized and in some landscapes termite mounds act as foci for nutrient redistribution. New information on the microbiology of termite mounds suggests that most are sites of diverse bacterial and fungal activity. Furthermore, the association between mound-building termites and the microbial population present in the structures has a synergistic effect on organic matter decomposition and hence nutrient cycling and availability. Examination of the effects of termite activity on plant production generally indicates a positive influence.
Random forests are a combination of tree predictors such that each tree depends on the values of a random vector sampled independently and with the same distribution for all trees in the forest. The generalization error for forests converges a.s. to a limit as the number of trees in the forest becomes large. The generalization error of a forest of tree classifiers depends on the strength of the individual trees in the forest and the correlation between them. Using a random selection of features to split each node yields error rates that compare favorably to Adaboost (Y. Freund & R. Schapire, Machine Learning: Proceedings of the Thirteenth International conference, ∗∗∗, 148–156), but are more robust with respect to noise. Internal estimates monitor error, strength, and correlation and these are used to show the response to increasing the number of features used in the splitting. Internal estimates are also used to measure variable importance. These ideas are also applicable to regression.
Their ability to degrade lignocellulose gives termites an important place in the carbon cycle. This ability relies on their partnership with a diverse community of bacterial, archaeal and eukaryotic gut symbionts, which break down the plant fibre and ferment the products to acetate and variable amounts of methane, with hydrogen as a central intermediate. In addition, termites rely on the biosynthetic capacities of their gut microbiota as a nutritional resource. The mineralization of humus components in the guts of soil-feeding species also contributes to nitrogen cycling in tropical soils. Lastly, the high efficiency of their minute intestinal bioreactors makes termites promising models for the industrial conversion of lignocellulose into microbial products and the production of biofuels.
The influence of Macrotermes falciger activity on clays, sesquioxides and water-dispersible clay (WDC) content was investigated by a physico-chemical, mineralogical and micromorphological study of termite mound and control soil profiles at various sites near Lubumbashi, SE Katanga, D.R. Congo. X-ray diffraction reveals that the termite-mound materials are enriched in 2:1 clays, especially mica and expandable clay minerals, and selective dissolution analyses show that they contain greater relative amounts of Mn oxides and poorly crystalline Fe oxides, relative to the surrounding Ferralsols. The water-dispersible clay (WDC) content is much higher (4–87 fold) in epigeal mound parts than in the control soils. Enrichment in 2:1 clays of the mounds is attributed to upward transport of mica and smectite as part of soil aggregates or saprolite materials used in mound construction. The difference in nature and abundance of sesquioxides between termite mound and control soil is related to a difference in moisture regime, whereby the basal part of the mounds are characterized by conditions with alternating reducing/oxidizing conditions, in contrast to the surrounding well-drained ferralitic soils. The much greater degree of clay dispersibility in termite mound materials than in the surrounding soils is mainly due to differences in clay properties, primarily surface charge characteristics, and to differences in Fe oxide content and mode of occurrence. The high water-dispersible clay content of termite mound materials is confirmed by micromorphological features, including abundant clay coatings and fragments of coatings.
In this study we assessed the species density and relative abundance of termites in peat land in Sarawak, Malaysia. Termites were sampled in nearnatural peat swamp forest, logged-over peat swamp forest, young oil palm plantation and a cleared and burned site. Species density and relative abundance were calculated for each site. Both species density and relative abundance differed significantly between sites. Near-natural peat swamp forest had the highest termite density, followed by logged-over peat swamp forest, young oil palm plantation and the cleared site. In contrast, the relative abundance of termites was highest in the young oil palm plantation due to the omnipresent genus Schedorhinotermes. Most of the species found in the cleared site and young oil palm plantation did not occur at the other sites. We conclude that ongoing forest degradation and conversion in tropical peat land result in shifting termite assemblages and declining species density. Species that originally occur at low densities in peat swamp forests are typically lost as a result of peat swamp forest conversion.
In Sahelian savannas, fungus-growing termites form biogenic structures made of soil or sheetings, on the soil surface and inside the soil, to protect themselves against heat, desiccation and predators while collecting food. The purpose of this study was to determine if analysis of the nematofauna can show differences in the way termites construct sheetings according to termite species or organic material harvested. In this study, soil nematodes, which were inactive during the experiment, were passively transported in soil pellets by termites when they built sheetings. Composition of the soil nematofauna was analyzed in sheetings produced when harvesting the four different types of different organic matter and in the soil around which these structures were produced. Three of the four organic materials were applied on soil as mulch whereas wood logs were inserted in the soil. Nematode density and diversity in sheetings produced by the three different termite species present (Ancistrotermes guineensis, Ondontotermes nilensis and Macrotermes subhyalinus) were similar in the four organic treatments except for sheetings constructed within the wood by A. guineensis. Nematode densities in sheetings were about ten-fold lower than in the 0–10 cm upper soil layer. Moreover, the composition of the nematofauna in sheetings was very different from that of the upper 10 cm, except for the sheetings built on wood. A finer comparison of the soil nematofauna in the top 7 cm of soil (separated in 0–0.25, 0.25–3.0 and 3.0–7.5 cm), and of fresh surface sheetings (produced within 24 h) showed that nematode composition of sheetings was very similar to that of the soil in the superficial strata (0–3 cm).
At the Lamto Savanna Ecological Station (Côte d’Ivoire), Odontotermes nr. pauperans (Termitidae, Macrotermitinae) was observed to build mounds enriched with fine particles. Using laboratory experiments we studied the selection of building materials by worker termites offered soil from two contrasting horizons: superficial soil (15‐20 cm) and a deeper layer (70‐80 cm). The physical and chemical properties of the unused soil and subsequent termite constructions (foraging galleries and fungus-comb chambers) were compared in each case. When presented with a single soil type, the termites modified soil texture for different parts of their structure. Termite building activity increased when presented with both soil types and a notable selection was observed in the use of a given soil type for a specific part of the structure built. We conclude that termites utilise soil particles selectively, favouring finer particles and making constructions which match ecological, physiological, and behavioural needs. Compared with material from deeper horizons, less energy was expended when surface soil was used as a resource for gallery building and less C and N supplementation was needed. In contrast, termites preferred deeper soil for constructing fungus-comb chamber walls because this material has greater water-holding capacity.
Fourteen types of physical structures produced by ecosystem engineers were sampled at the surface of a savanna soil of Colombia. Invertebrates implicated in the creation of these structures were identified. Some
physical (aggregate size and stability, bulk density) and chemical (C, N, P contents, pH, etc) properties of structures were assessed. Three large groups of structures were identified: (i) earthworm casts characterised by a high bulk density (1.3–1.4 g·cm–3), constituted of aggregates (7–10 mm), high in organic C (3–4 %) and assimilable nutrients; (ii) termite mounds with low bulk density (0.6–0.9 g·cm–3), constituted of aggregates (8–9 mm), high in organic C (3.5–10 %) and assimilable nutrients; and (iii) slightly compact (0.4–0.7 g·cm–3) and granular (aggregate size < 1.5 mm) termite superficial channels and ant mounds low in organic C (less than 1.5 %) and assimilable nutrients. These results underline the large diversity of the biogenic structures produced at the surface of the studied soil. They suggest the feasibility of a functional classification
of engineer organisms that would take into account simultaneously the different functional attributes reflected by these structures.
Soil-engineering organisms (earthworms, termites and ants) affect the soil and litter environment indirectly by the accumulation of their biogenic structures (casts, pellets, galleries, crop sheetings nests.). An enzymatic typology was conducted on six types of biogenic structures: casts produced by two earthworms (Andiodrilus sp. and Martiodrilus sp.), a nest built by a soil-feeding termite (Spinitermes sp.), crop galleries built by another soil-feeding termite (Ruptitermes sp.) and soil pellets produced by two species of leaf-cutting ant (Acromyrmex landolti and Atta laevigata) and an control soil from a natural Colombian savanna. A total of 10 enzymes (xylanase, amylase, cellulase, a-glucosidase, b-glucosidase, b-xylosidase, N-acteyl-glucosaminidase, alkaline and acid phosphatases and laccase) were selected to characterize the functional diversity of the biogenic structures. Our results showed that (i) Martiodrilus casts were characterized by a broad enzymatic profile that was different from that of the soil. (ii) A. laevigata pellets and termite structures had a profile broadly similar to the soil only with some enzymes (iii) Andiodrilus casts had an enzyme profile very similar to that of the soil. These results suggest that the functional diversity of these structures is related to differences between species and not to differences between taxonomic groups. For the first time, we evaluated differences in enzyme typology between biogenic structures collected on the same site but produced by different organisms. These differences suggested species dependent pathways for the decomposition of organic matter.
Earthworms and termites, as soil engineers, play a major role in the regulation of biogeochemical processes
and the provision of ecosystem services. They create biogenic aggregates on the soil surface, e.g.,
earthworm casts and termite sheetings, which can influence soil erosion and the downward transfer of
fertility. We assessed the effect of the micro-relief generated by earthworms and termites on soil hydrodynamic
properties, and soil and nutrient losses. Eighteen 1 m
×
1 m plots were established for rainfall
simulation experiments (2 runs of 40 min rain, intensity 90 mm h−1) in a steep slope fallow in Northern
Vietnam. The soil surface of the micro-plots differed in the proportions of earthworm casts and termite
sheetings. The results confirmed the importance of soil biostructures in the regulation of pedohydrological
properties of soils. Although globular water-stable earthworm casts promote water infiltration in soil
and decrease soil and nutrient losses, the unstable termite sheetings break-down rapidly and generate
structural crusts which foster water runoff and soil detachment. No relation was observed between the
abundance or biomass of earthworms or termites and the pedohydrological properties measured during
the rainfall simulations. This therefore suggests that soil engineers can have greater impact on ecosystem
functioning through their biogenic structures rather than as a result of their own abundance or biomass.
Chemical data are presented for a number of related topsoil, subsoil, and termite-soil samples collected in mulched coffee established on a laterized red loam coffee soil.
The comparisons of mean values for soil organic carbon, total base-exchange capacity, total exchangeable bases, exchangeable calcium, and exchangeable magnesium show that there is no statistically significant mean difference between the topsoil and termite-soil sample results. The subsoil sample results, however, are significantly lower than either the topsoil or termite-soil samples in all these results.
Similar comparisons of the mean values for soil pH and exchangeable calcium plus magnesium, when expressed as a percentage of the total exchangeable bases, show that the soil has been altered by Odontotermes badius(Hav.) in constructing the ‘runs; it is left with a higher pH value and with an increased proportion of the total exchangeable bases present as calcium plus magnesium.
It is not possible from these results to say conclusively whether the termite soil samples are derived from the adjacent topsoil or subsoil.
It is concluded that the presence of the termite soil which eventually becomes intimately mixed with the topsoil during cultivation and weed-control operations is not a point to be considered against Odontotermes badius(Hav.) when assessing the ‘pros and cons’ of its presence in mulched coffee.
Aim To (1) describe termite functional diversity patterns across five tropical regions using local species richness sampling of standardized areas of habitat; (2) assess the relative importance of environmental factors operating at different spatial and temporal scales in influencing variation in species representation within feeding groups and functional taxonomic groups across the tropics; (3) achieve a synthesis to explain the observed patterns of convergence and divergence in termite functional diversity that draws on termite ecological and biogeographical evidence to‐date, as well as the latest evidence for the evolutionary and distributional history of tropical rain forests.
Location Pantropical.
Methods A pantropical termite species richness data set was obtained through sampling of eighty‐seven standardized local termite diversity transects from twenty‐nine locations across five tropical regions. Local‐scale, intermediate‐scale and large‐scale environmental data were collected for each transect. Standardized termite assemblage and environmental data were analysed at the levels of whole assemblages and feeding groups (using components of variance analysis) and at the level of functional taxonomic groups (using correspondence analysis and canonical correspondence analysis).
Results Overall species richness of local assemblages showed a greater component of variation attributable to local habitat disturbance level than to region. However, an analysis accounting for species richness across termite feeding groups indicated a much larger component of variation attributable to region. Mean local assemblage body size also showed the greater overall significance of region compared with habitat type in influencing variation. Ordination of functional taxonomic group data revealed a primary gradient of variation corresponding to rank order of species richness within sites and to mean local species richness within regions. The latter was in the order: Africa > south America > south‐east Asia > Madagascar > Australia. This primary gradient of species richness decrease can be explained by a decrease in species richness of less dispersive functional taxonomic groups feeding on more humified food substrates such as soil. Hence, the transects from more depauperate sites/regions were dominated by more dispersive functional taxonomic groups feeding on less humified food substrates such as dead wood. Direct gradient analysis indicated that ‘region’ and other large‐scale factors were the most important in explaining patterns of local termite functional diversity followed by intermediate‐scale geographical and site variables and, finally, local‐scale ecological variables.
Synthesis and main conclusions Within regions, centres of termite functional diversity lie in lowland equatorial closed canopy tropical forests. Soil feeding termite evolution further down food substrate humification gradients is therefore more likely to have depended on the long‐term presence of this habitat. Known ecological and energetic constraints upon contemporary soil feeders lend support for this hypothesis. We propose further that the anomalous distribution of termite soil feeder species richness is partly explained by their generally very poor dispersal abilities across oceans. Evolution, radiation and dispersal of soil feeder diversity appears to have been largely restricted to what are now the African and south American regions. The inter‐regional differences in contemporary local patterns of termite species richness revealed by the global data set point to the possibility of large differences in consequent ecosystem processes in apparently similar habitats on different continents.
Although most researchers use the terms “guild” and “functional group” more or less synonymously, these two concepts bear different meanings. The guild concept refers primarily to the mechanisms of resource sharing by species in a competitive context whereas the functional groups concept is concerned with how a resource or any other ecological component is processed by different species to provide a specific ecosystem service or function. In many cases but not necessarily all, the two concepts are the two “faces” or “sides” of the same coin: the sharing by species of a similar resource is the guild facet (structural), while the ecosystem processes these species eventually perform through resource exploitation is the functional group facet. The two concepts differ in that competitive relationships within groups of species are not the focus of the functional group approach, exactly as processes or functions are not the focus of the guild approach. A group of species can be considered either as a guild or a functional group depending on the question addressed. Guild and functional group membership is independent of phylogenetic relationships but because species tend to share similar life history traits and adaptations through common evolutionary history, guild and functional group associates are often closely related. The concept of guild has had broader application in animal studies than in plant studies, whereas the reverse is true for the concept of functional group. Recent methodological advances to objectively partition species into guilds and functional groups, taking into consideration the most relevant characters or traits for delineating them, provide the means to construct an operational framework for making in situ and ex situ experiments that are urgently needed for a better understanding of the role of species in ecosystem functioning, especially in relation to global change concerns.
This work focuses on the interactions between fungus-growing termites (Isoptera, Macrotermitinae), clay particles and soil organic matter (SOM). As major bioturbators in tropical ecosystems, termites create biogenic structures (galleries, sheetings, nests, mounds, fungus-comb chambers) that strongly influence the physical and chemical properties of soils. Different kinds of substrates were given to Pseudacanthotermes spiniger, one of the main famous Macrotermitinae termite species in West Africa: (i) clay (mainly illite), (ii) a mix of sand and clay, or (iii) sand. When we proposed both clay and sand, we observed a high selection of clay by termites. Observation of the properties of biogenic structures by X-ray analysis showed that illite contained in the sheetings was strongly modified when compared to the bulk soil. We argue that the termite's saliva and/or the action of stimulated associate microorganisms have extracted un-exchangeable potassium, then leading to the creation of smectite layers. Thus, the termites P. spiniger, thanks to their building activity, can be seen as weathering agents of clay minerals. SOM content of the biogenic structures was found to be highly variable depending on the type of soil used (clay vs. sand) with enriched or impoverished C and N contents. Finally, we discuss how the auto-ecological requirements of termites (the balance between the cost of organic matter incorporation and the stability of the rehandled substrates) can affect soil and ecosystem functioning.
Termites play a significant role in soil-forming processes of the tropics. The influence of termites on pedogenesis as affected by the toposequence, however, has rarely been explored. We investigated the soil physicochemical and morphological characteristics of epigeal mounds constructed by Macrotermes bellicosus (Smethman) compared with those of surrounding pedons along a toposequence (bottom, fringe and upland sites) of an inland valley in central Nigeria. The physicochemical and morphological properties of the mound soils varied according to structural units but were generally different from those of the adjacent pedons. The differences included finer texture, higher electrical conductivity, total N, exchangeable bases (Ca, Mg and K) and effective cation exchange capacity and lower C/N ratio and exchange acidity in the mound than the pedon at each toposequence position. This tendency to modify the soil properties was more prominent in the nest body where the termites actually live, that is, in the hives, royal cell and base-plate, than in the soils below the nest and the other mound parts, that is, the external wall, internal wall and pillars. We found this trend to a greater or lesser degree at all toposequence positions. Our findings suggest that: (1) M. bellicosus can manipulate the mound soils according to functional applications of structure units or environmental requirements for its livelihood, regardless of local soils; (2) M. bellicosus makes ecological patches (hot spots) at all toposequence positions in the same measure; (3) the influence of M. bellicosus on the pedogenesis is reduced in the lowlands compared with the uplands because the number and volume of the mounds were substantially lower in the bottom and fringe sites compared with the upland site.
Termite mounds present a convenient record of the behaviour of their builders which can be studied at leisure. More usually, insect behaviour has results of a transitory nature, difficult to record and subject in their interpretation to the personal idiosyncrasies of the observer. A behaviour pattern which is specific to a particular termite may, however, result in mounds which appear superficially different under different environments, while two different species may produce mounds which appear to be similar in the same environment. It follows that the use of termite mounds as indications of species behaviour must be considered with care if there are wide differences in environmental factors in the areas being dealt with.
The following remarks arise mainly from observations made in Eastern Africa on the large mounds constructed by three species of the genusMacrotermes. Of these,Macrotermes bellicosus (Smeath) is the most widely distributed, occuring from Eritrea (and Aden) in the north to the borders of the Union of South Africa in the south, from sea-level to 1 800 metres, under most conditions other than tropical rain forest and desert sand.Macrotermes natalensis (Hav.) andMacrotermes goliath (Sjost.) have more restricted distributions within the range ofbellicosus.