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Despite the large contribution of macropores made by soil engineers to the soil macroporosity and water infiltration, few studies have addressed the specific contribution of soil engineer groups, dynamics of biopores and their efficiency in conducting water. Thus, we aimed to investigate the link between soil macrofauna, soil biopores and water infiltration under different pedoclimatic conditions. To do so, we conducted an experimentation in twelve study sites with a large longitudinal gradient from France to Vietnam. The experiment consisted in the field incubation of repacked soil in cores (15 cm in height and 15 cm in diameter) and controlling the activity of soil engineers in the manner of litter bag. For each site, soil columns were: (i) covered with a mesh (200µm) or not and (ii) with or without addition of organic residues to the soil surface. After 12 months, we measured (i) the 3D organization of biopores by X-ray computed tomography and (ii) the saturated hydraulic conductivity by Beerkan method. In addition, soil macrofauna communities and the 3D organization of biopores was measured in each study field. Addition of organic residues increased up to 2-fold the volume percentage of biopores which reached similar values than those observed for each study field. The co-inertia analysis between the data matrix characterizing the shape of biopores and the data matrix of the macrofauna communities showed no statistically significant correlation. Saturated hydraulic conductivity increased with the presence of biopores by 2 to 50-fold with the lowest increased in soils presenting largest saturated hydraulic conductivity. In conclusion, these results demonstrated that biopores are rapidly regenerated regardless the pedoclimatic conditions while the efficiency of biopores in conducting water is related to soil properties.

International audience; In the Lower Mekong Basin, paddy fields often appear as mosaics, with soil mounds covered by trees or other plants in a spotty distribution. These soil mounds are commonly named termite ‘lenticular mounds’ because termite bioturbation is considered to be at their origin. Termite mounds host a large diversity of animals and plants, increasing landscape patchiness. Because the preservation of these islands of biodiversity is threatened by modern agricultural practices, the aim of this study was to quantify their abundance and the services they provide to the local population. The abundance of mounds and their use by the population were quantified in a catchment in Cambodia. We found that mounds density reached ~2 mounds ha−1. Interviews carried out within the catchment showed that most of the interviewees used mounds for increasing the fertility of their field and for the cultivation of rice and other plants (e.g. sponge gourd and pumpkin). In addition to their potential to increase plant productivity, the survey revealed that animals (rats and snakes), mushrooms and 13 plant species found on or in mounds were consumed by the population. In addition to potentially contributing to an increase in food diversity, mounds also impacted farmers' health by allowing access to 20 medicinal plant species and indirectly via a reduction in pesticide use. In conclusion, this study is the first attempt to quantify the large number of services provided by termite mounds in Cambodia. This increase in the knowledge of the diversity of environmental and socioeconomic services provided by termite mounds is likely to contribute to their preservation and provide a basis for the sustainable management of biodiversity in paddy fields in the Lower Mekong Basin region

The role of earthworms on biogeochemical carbon cycling is a major knowledge gap resulting from the difficulty of isolating and exploring the effects provided by the diversity of organisms. In this study, we investigated the effect of six earthworm species belonging to three ecological categories on soil organic carbon (SOC) mineralisation. To this end, we produced casts with the six species using subsoil material with low SOC content and miscanthus litter. Cast were subjected to laboratory ageing for 140 days. During this process, we monitored physicochemical parameters, CO2 emissions and determined the micro-scale organisation of the casts’ particulate organic matter and pores using X-ray tomography.Our results showed contrasting properties of fresh casts from the 3 main ecological categories, in accordance with the earthworm species’ morphological or behavioral strategies, indicating that those were maintained in artificial environments. However, species-specific changes in cast properties throughout ageing increased intragroup variability among ecological categories. As a result we observed earthworm species-specific evolution of CO2 mineralisation rates during casts ageing. We found that at least half of the variability in CO2 emissions was explained by cast microstructural changes, related to the spatial arrangement between particulate organic matter, porosity, and mineral particles. We conclude that earthworm species-specific traits may play a role in organic carbon protection through their impact on microstructural cast properties.

International audience; Classifying organisms has a wide use and a long history in ecology. However, the meaning of a ‘group of organisms’ and how to group organisms is still the subject of much theoretical and empirical work. Achieving this long quest requires simplifying the complexity of species niches for which relevant morphological, behavioural, biochemical or life-history traits are often used as relevant proxies. Soil fauna is highly diverse and many classifications have been proposed to synthesize both the response of soil organisms to their environment and their effect on soil functioning. Here, we provide a critical overview of the characteristics and limitations of the existing classifications in soil ecology, and propose clarifications and alternatives to current practices. We summarise the similarities and differences in how classifications have been created and used in soil ecology. We propose a harmonization of the current concepts by properly defining ‘guilds’, ‘functional groups’ and ‘trophic groups’ as subcategories of ‘ecological groups’, with different purposes and distinguishing criteria. Finally, based on these concepts, we suggest a common framework to define classifications based on functional traits that allows a better and unified understanding of changes in soil biodiversity and ecosystem functioning.

This study aimed to compare the properties of the constructions made by Microcerotermes pakistanicus, a wood-feeding termite species building carton nests, to those made by the fungus-growing termite Odontotermes obesus in a secondary forest in the Western Ghats region of Kerala. X-ray computed tomography (X-ray CT) showed that the pinnacle of O. obesus termitaria was very thick and compact with a central cavity and numerous unconnected galleries in its inner part. Conversely, the construction of M. pakistanicus appeared as a very porous media made of abundant and connected galleries following a radial trajectory, and the galleries were separated from the others by a thin wall. Despite significant differences in terms of soil chemical properties, Odontotermes obesus termitaria and sheetings had similar properties to those of the surrounding topsoil. Conversely, M. pakistanicus nest had unique chemical properties distinct from those of O. obesus or the surrounding soil. Moreover, although M. pakistanicus builds carton nests from its faeces, minerals were also measured within its termitaria. In conclusion, this study shows the very different properties of O. obesus and M. pakistanicus constructs. It also suggests the need for soil ecologists to consider carton-nests as a third group of soil-nest type, in addition to those built by soil or litter feeders and fungus-growers which edify termitaria from soil and different amount of organic matter. Further studies are also needed to determine their functional impacts on soil and nutrient dynamics.

International audience; 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.

The utilization of termite mounds for the improvement of soil fertility is a worldwide practice and usually explained by the specific properties of this biogenic material. In Cambodia, farmers also use termite mound soils as amendments with the aim to improve the fertility of paddy fields. The first objective of this study was, therefore, to describe the physical and chemical properties of this material and, consequently, to determine its potential for improving soil fertility. A second objective was to consider farmer’s perception and to quantify the diversity of services provided by termite mounds. We confirmed the specific soil properties of termite mounds but showed that their positive influence on soil chemical fertility and water retention are only significant in very sandy soil (>80% sand) while they remain limited in less sandy soil (~40 and 60% of sand). However, termite mounds are considered useful by farmers independently of the soil condition, mostly because this soil material is considered to positively increase soil fertility but also because they host a specific biodiversity which can be used for medicinal purposes or because consumed, then increasing population livelihood. Our work shows the discrepancy between the perception of farmers and the real impact of termite mounds on soil fertility as well as the diversity of services delivered by biodiversity in paddy fields.

International audience; This study was aimed to evaluate the potential of four earthworm species commonly found in South China for the bioremediation of soils contaminated by Cu, Cd, Pb and Zn. Survival rates and metal accumulation of Eisenia fetida, Amynthas morrisi, A. robustus and A. corticis and changes in soil physico-chemical properties were investigated in a 60-day incubation experiment with a metal-polluted soil. At the end of the experiment, the survival rates of E. fetida, A. morrisi and A. robustus were significantly higher than that of A. corticis. Principal component analysis showed that earthworm activity improved soil quality with the averaging soil quality index being 0.66, 0.64, 0.56, 0.53, and 0.12 for the A. corticis, A. morrisi, A. robustus, E. fetida, and control treatments, respectively. The highest total available Cd, Cu, and Pb in casts were found in the treatment with A. morrisi, and this species accumulated the smallest amount of metals. Results indicate that A. morrisi may be the best candidate for earthworm-assisted bioremediation of metal contaminated soils in South China.

International audience; Wind erosion is a major threat to the sustainability of arid and semi-arid ecosystems. In these environments, biological soil crusts positively impact soil resistance to erosion. Less is known, however, on the impact of soil bioturbation by animals. In Southern Tunisia, bioturbation is mainly carried out by termites, ants and rodents which deposit mineral and organic components on the soil surface in the form of soil sheetings for termites or as soil heaps for ants and rodents. We here question the properties of these soils and measure their resistance to wind erosion. We showed that soil sheetings are made of sand grains linked together by bridges of organic matter, clay particles and other small size minerals such as carbonates and gypsum. The stability of these aggregates is comparable to that of biological soil crusts, despite their very different organizations. Conversely, the soil excavated by ants and rodents mainly consists in individual sand grains, which are impoverished in organic carbon and prone to wind erosion. In conclusion, this study highlights the importance of termites, as key soil bioturbator, on the dynamics of soil aggregates in Southern Tunisia. It also shows that they have an opposite effect than that of ants and rodents on the resistance of soil to erosion.

International audience; 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.

International audience; Earthworm cast ageing controls soil ecosystem services such as carbon storage and nutrient availability. To test the hypothesis that biogeochemical changes during casts ageing can be traced by infrared spectroscopy, we collected topsoil aggregates and earthworm casts produced by the anecic earthworm Amynthas khami belonging to five distinct degradation stages in woodland in northern Vietnam. We analysed mid-infrared (MIR) spectra of both sample types using two approaches: (1) calculation of the proportion of aliphatic compounds and the humification index of organic matter (OM) using specific wavenumbers and (2) linear discriminant analysis (LDA) of the most important peaks and shoulders of the entire spectrum. Our results showed that aliphatic compound contribution to OM was similar and the humification index of OM lower (2-fold) in casts as compared to topsoil aggregates independent of their degradation stage. In contrast, LDA showed a continuous shift from fresh casts to aged casts and topsoil aggregates in agreement with biogeochemical changes of cast properties. We thus conclude that MIR analysis of bulk samples and LDA taking into account the absorbance intensity of most important wavenumbers is a promising tool to capture biogeochemical alterations of organic and mineral earthworm cast properties during ageing.

International audience; Soil macroporosity is a highly dynamic feature driven by numerous physical and biological processes, of which bioturbation, the movement of water in soil and swelling and shrinking cycles are the main processes. To date, the interaction between these factors, especially how galleries produced by soil fauna respond to rainwater percolation and wetting-drying (WD) cycles, remains poorly known. A laboratory experiment was carried out to expose soil macrofauna galleries to 3 different consecutive water flow (simulated rain event of 50, 80 and 110 mm h-1 in one hour) and drying cycles in a clayey soil. X-ray computed tomography and image analyses were used prior and after each exposure to assess the water stabilities of galleries and created cracks. The 3D properties (volume, diameter, specific surface area and density) of the galleries produced by termites or ants were not statistically influenced by rainwater percolation and WD cycles, suggesting a high water stability and life expectancy under natural conditions. Conversely, the crack water stability was variable and was probably influenced by the presence of galleries in the same area. This study emphasizes that the macropores created by soil fauna may persist in clayey soil and that there is a need to better understand how cracks and galleries interact.

Organic amendments may improve the quality of acidic tropical agricultural soils with low organic carbon contents under conventional management (mineral fertilization and irrigation) in Southeast Asia. We investigated the effect of biochar, compost and their combination on maize growth and yield, soil physical, biological and chemical properties at harvesting time at four sites in three countries: Thailand, Vietnam and Laos. Treatments consisted of 10 t·ha−1 cow manure compost and 7 t·ha−1 of Bamboo biochar and their combination. Maize biomass production and cop yields were recorded for two seasons. Elemental content, pH and nutrient availability of soils were analyzed after the first growing season. We also characterized macrofauna abundance and water infiltration. Few changes were noted for maize biomass production and maize cop yield. Soil chemical parameters showed contrasting, site-specific results. Compost and biochar amendments increased soil organic carbon, pH, total K and N, P and K availability especially for sandy soils in Thailand. The combination of both amendments could reduce nutrient availability as compared to compost only treatments. Physical and biological parameters showed no treatment response. We conclude that the addition of compost, biochar and their mixture to tropical soils have site-specific short-term effects on chemical soil parameters. Their short-term effect on plants is thus mainly related to nutrient input. The site-dependent results despite similar crops, fertilization and irrigation practices suggest that inherent soil parameters and optimization of organic amendment application to specific pedoclimatic conditions need future attention.

Interactions of earthworm species with their environment and in particular the soil they inhabit is poorly understood. In this study, we aimed to use mid infrared absorption (MIR) spectroscopy of earthworm bodies in combination with discriminant analysis of principal components (DAPC), in order to investigate if their biogeochemical composition is determined by their species belonging or the soil they inhabit. Our conceptual approach included the comparison of MIR spectra of four earthworm species (Lumbricus terrestris, Allolobophora chlorotica, Aporrectodea caliginosa and Aporrectodea icterica) sampled from four different agricultural fields in France. Moreover, we tested the influence of the habitat on the earthworm MIR spectra by exchanging individuals and soils in an incubation experiment. MIR spectra varied according to species and sampling site. The MIR spectra of earthworm bodies also changed during the incubation experiment, and for L. terrestris, A. chlorotica and A. icterica depended on the properties of the soil ingested. This suggested that the food source in different habitats impacted the biogeochemical composition of earthworm bodies. DAPC allowed for the identification of earthworm species ranging from 64 to 100% of accuracy (mean 78%). We thus conclude that MIR spectroscopy may be a suitable approach to identify earthworm species, but that their signature may also allow to investigate their ecology as determined by the soil they inhabit.

International audience; By creating vertical and continuous burrows, anecic earthworms accelerate the transfer of water in soils. However, the degradation mechanisms and lifespan of burrows and the consequence of changes in burrow characteristics for water infiltration remain poorly known. In this study, the dynamics of the degradation and hydraulic properties of burrows made by the anecic earthworm Amynthas khami in a clayey soil were investigated in a meadow and in a woodland in North Vietnam. We selected three categories of surface casts, namely, (i) fresh (a few days old), (ii) dry (>1 month old) and (iii) degraded by rain (older than the dry casts), as proxies of the age of burrows. The physical and chemical properties of casts were measured and compared to the surrounding soil aggregates without visible earthworm activity (control). Soil cores were sampled below casts and control and the 3D structure of burrows was characterized using X-ray tomography. Then, water infiltration was measured in the saturated soil cores. Fresh and degraded casts had a lower water stability than control aggregates, whereas higher values were found in dry casts. Water infiltration was twice higher in columns below fresh and dry casts than in the control. However, below degraded casts, the positive effect on water infiltration was reduced or disappeared in some cases. The degradation of burrows led to significant increase in the specific surface area, decrease in their minimum diameter and increase in the abundance of cracks connected to burrows. Our results indicate that anecic burrows persist at least for months below degraded casts but that aging due mainly to physical processes reduces water infiltration. This study highlights the importance of taking into account the lifetime of burrows in the soil when assessing the effect of earthworms on soil structure and water transfer.

The transformation of organic matter (OM) occluded in earthworm casts during the casts' lifetime may affect its composition and accumulation in stabilised OM pools. We collected casts produced by the anecic earthworm Amynthas khami in a tropical woodland of Northern Vietnam presenting different degradation stages. The aim of this study was to assess (1) the biogeochemical properties of OM in earthworm casts compared to control aggregates from the surrounding soil, and (2) the fate of occluded OM during cast ageing. We analysed intact casts and their density fractions at five ageing stages for organic carbon (OC) and nitrogen (N) content, OM chemical composition by analytical pyrolysis, and OM stability by Rock-Eval thermal analysis. Compared to control aggregates, fresh casts had higher OC values (5.3 vs. 2.6%) and increased OC in all density fractions. Cast OM had more lignin (1.1 vs.

International audience; 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.

Heterogeneous physiognomy and observed diversity of woody vegetation in savanna are considered as specific responses of seedling species during their growth to the given site characteristics changeable with time. Consequently, understanding early plant attitude using different growth soil is an important indicator in choosing species to introduce or to assist natural or artificial regeneration to the extent that establishment and productivity of plant species are not solely controlled by the effects of habitat modification and/or environmental resource availability but mostly by seedling quality. This study focused on comparative assessment of growth performance and adaptive traits of early seedlings of Balanites aegyptiaca, Diospyros mespiliformis and Tamarindus indica three multipurpose species between of Macrotermes subhyalinus mound and surrounding area in order to understand the attitudes of woody species hosted by termite mounds. Seedlings of similar age per species were grown in plastic bags as pots containing composite soils sampled till a depth of 30 cm on mounds and surrounding area in Tiogo state forest and of which the amount of retained water, carbon (C), nitrogen (N), calcium (Ca), magnesium (Mg), assimilable phosphorus (ass. P) and potassium (K) were quantified prior to growth experiment. Height and collar diameter of seedling stems, final length and diameter of the main root were measured; the total dry biomass of root and shoot and, root to shoot ratio were evaluated for seedlings up to 5 months relating to the soil origin. Mean values of retained water and selected nutrients were higher for mound soil than for surrounding soil. Besides, the studied parameters of T. indica seedlings were significantly higher for mound soil than those recorded for surrounding soil (P

Environmental changes are threatening current and future food security. In this context, it is imperative to design agricultural systems that are resilient to increasing frequent climate shocks, losses in biodiversity and soil fertility and to increasing demand from our societies because of population growth and consumption patterns. The emergence of sustainability science reminds us that soil management cannot be successfully approached by the independent actions of individual categories of actors, namely soil researchers or agronomists. Therefore, we advocate for more holistic and transdisciplinary research that takes into account the social, cultural, environmental and economic impacts of agricultural practices. Using examples of agricultural practices that aim to use the activity of termites to improve the services delivered by ecosystems (e.g. the Zai system), rather than considering them pests and trying to eradicate them from lands, we discuss the interest of traditional agricultural practices as sources of inspiration for soil scientists and for the identification of tomorrow's agricultural practices.

Si is one of the most abundant element on earth and an abundant literature shows its beneficial effects on plant growth and resistance. We here question the influence of termites, as key soil bioturbators, on the distribution of Si in a tropical soil. The abundance and forms of Si in termite mounds build by Odontotermes obelus (TM) or in the soil eroded from TM but redistributed on the ground surface (EROD) were compared to those measured in the 0-5 (Ctrl(0-5)) and 70-120 cm soil layers (Ctrl(70-120)). Although termites use the soil from Ctrl(70)-(1)(20) for building their mounds, we found that TM and EROD had intermediate soil physical, chemical and mineralogical properties between Ctrl(0-5) and Ctrl(70)(-1)(20). Clay content was not significantly different between soil materials. However, the lower variability measured in TM than in the soil suggested that termites used soil layers with higher amounts of clay fraction and with a preference especially for layers enriched in 2:1 clay minerals (smectite) most likely because they provide better physical properties in terms of plasticity and water retention than kaolinite. Finally, phytoliths and bioavailable Si (Si-CC) contents were increased in TM in comparison with Ctrl(70)(-1)(20), suggesting an incorporation of phytoliths in termite construction through their saliva and/or an increasing availability of Si-CC from the minerals. In conclusion, this study highlights how termites, through their feeding and building activities, impact Si distribution in tropical soils.

Termites are amongst the main macroinvertebrate decomposers in tropical ecosystems and they exert additional impacts through the creation of biostructures (mounds, galleries, sheetings, etc.) with different soil physical and chemical properties, thereby impacting positively on numerous ecosystem services for humankind. Unfortunately, this positive or 'bright' role of termites is often overshadowed by their 'dark' side, that is, their status as pests threatening agriculture and constructions. This article assesses advances in our knowledge of the impact of termites on several sustainable development goals (SDGs 1 'no poverty', 2 'zero hunger', 3 'good health', 9 'innovation', 11 'sustainable cities', 13 'climate action' and 15 'life on land'). Finally, using the Indian myth of Valmiki as a parable, we illustrate that a reconciliation between the termite's dark and bright sides is needed if we want to reduce our dramatic impact on biodiversity and more generally achieve SDGs.

In this study, we used Mid-Infrared Spectroscopy (MIRS) to analyze the biochemical fingerprints of nine termite colonies (soldiers, minor and major workers). We then examined whether these spectra could be used to differentiate termite colonies and if their differences could be explained by the geographical distances between colonies and/or their ages. We demonstrated that when only data from the heads of minor workers were considered, the specific fingerprint of each colony appeared to reflect its coordinate position in the study site. However, termite mound height, a proxy for colony age, was the main factor governing these signatures when data from the abdomen of major workers were used. Thus, this study shows the potential of MIRS for differentiating termite colonies in the field. It also highlights the close relationship between the physiological states of termite colonies and their environment.

International audience; Soil is considered as a non-renewable resource, which may be lost in sloping land more rapidly than it is formed thus leading to loss of fertility and ecosystem deterioration. We hypothesized that earthworms could counteract this process due to their cast forming activity. To test this hypothesis, we quantified the production of casts in small plots of 0.25 m2 established in three vegetation units (woodland, shrubland and meadow) in a catchment of 46 ha for 2.5 years in relation to their (micro-) pedoclimatic conditions. We also assessed the impact of cast formation on water runoff and soil detachment. Moreover, we quantified the mass of casts deposited in the entire catchment on a regular grid of 50 m and we measured soil erosion at the outlet of the catchment. Our results showed a high and variable production of casts (from 16 to 219 t ha−1 year−1) depending on vegetation, season and year. The mass of casts found in the entire catchment represented on average 7.4 t ha−1 with an annual production rate of 35 t ha−1. Since the annual erosion rate measured for the entire catchment (3 t ha−1 year−1) was much lower than the cast production rate, our results indicated that most of the soil bioturbated by earthworms remained in the catchment. Indeed, water runoff and soil detachment measured in small plots showed that casts were not transported in the water runoff but degraded by raindrop impacts with the material remaining at the place of deposition. This process led to the generating of a new soil horizon at the culmination point of the catchment of up to 6.5 cm after 2.5 years. We conclude that the surface activity of anecic earthworms could influence soil generation at scale and conteract the effects of soil erosion.

Several fungus-growing termite species build mounds, or termitaria, that are conspicuous features of African and Asian landscapes. Studies of the genus Macrotermes in Africa have established that their mounds provide an environment buffered against extremes of temperature and humidity, as well as protection from predators, and are correspondingly modified in composition. However, no studies are available in the specific context of the Asian continent where termite mounds are also abundant. Hence this study focused on the abundance and properties of mounds built by Odontotermes obesus in relation to rainfall and parent soil properties in southern Indian forests, in the Western Ghats area. Termite mound densities and sizes were measured in 18 forests along a rainfall gradient from 1160 to 3670 mm yr(-1). The C and clay contents were analyzed in soil samples collected from mounds and the surrounding topsoil. Mound numerical density was positively correlated with mound height and rainfall had a negative relationship with the abundance. Neither vegetation type nor or rainfall influenced the clay content in the mound walls but a positive linear relation was observed between the clay content in the termite mound wall and that in the surrounding topsoil environment, suggesting a rather low impact of termites on the clay content in the mound soil. The C content in mound walls depended mainly on how much clay the termites used. In conclusion, this study shows that the amount of rainfall affects the abundance of O. obesus mounds in India while the amount of clay in the surrounding topsoil determines mound soil properties. (C) 2016 Elsevier B.V. All rights reserved.

Understanding the link between termites' impact on ecosystem functioning and their ecological needs remains a key question in ecology. This study focused on the influence of the fungus-growing termite species, Hypotermes obscuriceps, on soil properties in Southern India. This species produces soil sheetings and mounds on the ground. In contrast to other termite species, such as those belonging to the Macrotermes and Odontotermes genera, which produce mounds to live in, H. obscuriceps excavates soil above ground for constructing its chambers below ground. Using a captive colony of H. obscuriceps growing up in control conditions, we measured the soil properties (carbon content, particle size distribution, pH, electrical conductivity and concentration in soluble anions and cations) of its mound and of the sheetings it produced over the leaves of Acacia auriculiformis and on the branches of Ipomoea carnea and Lantana camara. The physical and chemical properties of H. obscuriceps mounds were very similar to those of the surrounding soil and even if rain erodes these mounds in the field, it is likely to have only a small effect on the resulting run-off water quality. In contrast, sheetings have higher clay and C contents than the surrounding soil. Their degradation by rain is likely to be associated with soil detachment and F-, Cl- and K+ export in water runoff and/or leachate. In conclusion, this study shows that this species impacts soil properties more through the construction of sheetings than mounds. This difference is explained by the ecological needs of termites. While H. obscuriceps is not dependent on soil mound properties for survival, soil sheetings' properties are essential for providing them a protective cover.

This study aimed to understand the relationship between termite food preferences and the ecological benefits derived from their activity in terms of soil dynamics and water infiltration. A field study was carried out for six months with different food baits (elephant dung, Acacia leaves, twigs and leaves of Lantana camara as well as Ficus religiosa, Pterocarpus marsupium, Prosopis juliflora, Michelia champaca, Azadirachta indica and Hevea brasiliensis wood stakes) installed on the soil surface in a semi-deciduous forest in southern India. At the end of the experiment we determined bait consumption rates and the amount of soil sheetings covering the different baits. Water infiltration rates were also measured using the Beerkan method. The initial infiltration rates (i.e. average of the first three infiltration rates) under the baits were compared to those at the end of the experiment (average of the last three infiltration rates when the steady state was reached). Three termite species, Odontotermes obesus, O. feae and Microtermes obesi, were found associated with some of the baits in the study area. Among the different baits, elephant dung and Acacia leaves were the most preferred and a relationship was observed between the quantity of soil sheetings and the bait consumption rate. Termite preference for elephant dung and Acacia leaves was also associated with higher water infiltration rates. However, this difference was only significant at the beginning of the experiment and no significant difference was measured once the steady state was reached. In conclusion, we showed that resource quality was of primary importance for soil sheeting production but that the influence of termites on water infiltration remained limited, most likely because of the low stability of their tunnels in the soil.

Termites are undoubtedly amongst the most important soil macroinvertebrate decomposers in semi-arid environments in India. However, in this specific type of environment, the influence of termite foraging activity on soil functioning remains unexplored. Therefore, this study examines the link between the quality of litter and the functional impact of termite feeding preferences on soil properties and soil hydraulic conductivity in a deciduous forest in southern India. Different organic resources (elephant dung: &ldquo, ED&rdquo, elephant grass: &ldquo, EG&rdquo, acacia leaves: &ldquo, AL&rdquo, and layers of cardboard: &ldquo, CB&rdquo, ) were applied on repacked soil cores. ED appeared to be the most attractive resource to Odontotermes obesus, leading to a larger amount of soil sheeting (i.e., the soil used by termites for covering the litter they consume), more numerous and larger holes in the ground and a lower soil bulk density. As a consequence, ED increased the soil hydraulic conductivity (4-fold) compared with the control soil. Thus, this study highlights that the more O. obesus prefers a substrate, the more this species impacts soil dynamics and water infiltration in the soil. This study also shows that ED can be used as an efficient substrate for accelerating the infiltration of water in southern-Indian soils, mainly through the production of galleries that are open on the soil surface, offering new perspectives on termite management in this environment.

Mounds built by fungus-growing termites are often considered to be patches or fertile areas in tropical ecosystems because they contain more nutrients than the surrounding soil environments. However, the mechanism of how these habitats influence soil physical properties remains unknown. Therefore, this study aimed at comparing the soil hydrostructural properties of two common termite mounds in southern India, namely, cathedral and lenticular mounds. The shrinkage curves of the soil eroded from three cathedral mounds and of the soil sampled in the center or in the periphery of three lenticular mounds were measured and compared to those of their surrounding soil environment. This study revealed that the soil in the periphery of cathedral mounds was compact with a lower soil specific volume and macroporosity than the control soil. On the other hand, the accumulation of clay in lenticular mounds was associated with a lower soil specific volume at the end of the shrinkage period, higher microporosity, increased swelling capacity and higher water holding capacity than the control soil. These parameters reached intermediate values in the periphery of the lenticular mounds between those of the lenticular mound soil and the surrounding control soil. In conclusion, this study showed that cathedral and lenticular mounds impacted soil hydrostructural properties in two opposing directions. It also highlighted the link between the impact of termites on the clay and carbon contents of soil and their influence on soil porosity and water dynamics, and then the need for a better understanding of the influence of termites on the dynamic of carbon and clay in ecosystems.

This communication assesses advances in our knowledge of the beneficial influences of termites on ecosystem functioning and services. Termites are amongst the main macroinvertebrate decomposers in arid and semi-arid environments and exert additional impacts through the creation of biostructures (mounds, galleries, sheetings, etc.) with different soil physical and chemical properties . Unfortunately, the positive ‘or bright’ role of termites is often overshadowed by their dark side, i.e. their status as pests threatening agriculture in the tropics (635 vs. 164 articles referenced in WoS with termites and either pest or ecosystem engineer as keywords. Source: WoS, April 2019). 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 [1] . In this communication, two examples of ecosystem services provided by termites are given. The first describes the positive impact of termites on water infiltration and nutrient guidance at small scale through the production of foraging galleries in soil [2] and how this activity can be used to improve agro-ecosystem functioning in arid and semi-arid environments [3] . The second example deals with the construction of mounds and sheeting by termites in “natural” environments [4] and how these “patches of biodiversity and fertility” can be used in the lower Mekong Basin to reduce food insecurity and to provide a better access to health [5] ( Fig. 1 ). Finally, the perception of termite mounds in Southern Indian rural environments ( Fig. 2 ) is discussed and used as example of the cultural services that can be provided by termites in some circumstances. The story of Valmiki, the author of the Ramayana, is explained and used as a parable for highlighting the interconnection between the “bright” and “dark” sides of termites, and more generally that to get the bright we also need the dark.

International audience; In the tropics, termites are key litter decomposers and soil bioturbators. Termite foraging activity involves the production of sheetings and galleries that influence the physical, chemical and hydraulic properties of soils. The functional impacts of these biogenic structures and biopores have been acknowledged for a long time in soils dominated by 1:1 minerals. Less is known, however, on their functional impacts in soils dominated by 2:1 minerals, such as vertisol which represent 22% of the land surface in India. Therefore, an experiment was carried out in a vertisol in southern India where elephant (Elephas maximus) dung pats (ED) and Lantana camara twigs (LT) were applied on the ground and protected (+) or not (−) from termite activity. Termite activity was only measured below ED−, showing a clear preference for organic matter derived from elephant dung. Soil sheetings had similar properties to the surrounding topsoil, with the exception of their C content that was reduced. This result raised the question of the origin of the soil used by termites for covering ED. ED− was also associated with the presence of effective macropores up to 5 cm depth and a significant increase in water hydraulic conductivity (12-fold). However, the utilization of the coefficient of linear extensibility showed that these galleries were unstable and most likely short-lived. In conclusion, this study confirmed that the structure of soils dominated by 2:1 minerals is mainly controlled by physical processes (i.e., the shrinking and swelling of soils). This study also stresses the need to better understand the dynamic of termite galleries in soil and to quantify the origin and fate of organic matter in soil sheetings.

Despite the acknowledged roles of termites in tropical ecosystems, the majority of published studies of epigeal mounds still address the African fauna and are principally concerned with spatial patterns and putative inter-colony competition, rather than the links between parent soil properties and mound establishment. Further, information about the effects of habitat disturbance, and especially fragmentation, is lacking. This study assessed the abundance and distribution of the cathedral- and lenticular-type aboveground mounds of fungus-growing termites (Macrotermitinae), which are a common feature of South Indian woodlands, in relation to soil properties (vertisol vs. ferralsol) and habitat fragmentation (forest vs. highway margins). Mound abundance averaged 3.5 (standard error, SE 0.8) ha(-1) (cathedral) and 12.9 (SE 2.1) ha(-1) (lenticular), but was not influenced either by soil properties or disturbance. However, the volume of soil stored in the mounds varied between 27 (SE 8) m(3) ha(-1) (ferralsol) and 47 (SE 6) m(3) ha(-1) (vertisol). At the watershed scale, such volumes are equivalent to a 3.1-mm layer of soil if spread evenly across the landscape, roughly the same as the estimated erosion over the life of a typical mound. Significantly more nutrients were stored in lenticular mounds, especially on the vertisol, but the significance of these at the ecosystem level was considered small. In conclusion, this study suggests that termite mounds, and especially lenticular mounds, have a significant impact on soil dynamics at the watershed scale but a limited impact on the distribution of C and nutrients.

Termites are considered soil engineers due to their effects on soil properties in tropical ecosystems, which include the production of biogenic aggregates with different physical and chemical properties to the surrounding environment. How termites influence the dynamics of aggregates on the soil surface is still poorly understood. In this study, we sampled 50-250, 250-2000 and >2000 mu m soil aggregates from the wall of termite mound nests produced by Odontotermes obesus (Blattoidea, Macrotermitinae subfamily) in a Ferralsol and in a Vertisol in Southern India and analyzed their stability in water and to ultrasonic agitation. Our study shows that the influence of termites on the stability of soil aggregates varies depending on the properties of soil. The concentrations in C and N were lower in termite mound soils compared to the control soil aggregates in the Ferralsol for all the soil aggregate size fractions whereas in the Vertisol, the C and N contents were only lower in soil aggregates >2000 mu m (i.e., no significant difference for aggregates 250 mu m in the Vertisol. Since micro-aggregates

Soil shrinkage curve represents a decrease of total porosity or an increase of bulk density with water loss. However, our knowledge of the dynamics of pores and their geometry during soil shrinkage is scarce, partially due to lack of reliable methods for determining soil pores in relation to change in soil water. This study aimed to investigate the dynamics of macropores (>30 mu m) of paddy soils during shrinkage. Two, paddy soils, which were sampled from one paddy field cultivated for 20 years (YPF) and the other one for over 100 years (OPF), represented difference in crack geometry in the field. Macropore parameters (volume, connectivity, and orientation of pores) and soil shrinkage parameters were determined on the same undisturbed soil cores by X-ray microtomography and shrinkage curve, respectively. Macroporosity was on average four times larger in the YPF than in the OPF whereas the shrinkage capacity was lower in the YPF as compared to the OPF (0.09 vs. 0.15 COLE). Soil shrinkage increased the volume of pores by 3.7% in the YPF and by 1.6% in the OPF as well as their connectivity. The formation of macropores occurred mostly in the proportional shrinkage phase. As a result, the slope of the proportional shrinkage phase was smaller in the YPF (0.65) than in the OPF (0.89). New macropores were cracks and extended pre-existing pores in the range of 225-1215 pm size without any preferential orientation. This work provides image evidences that in paddy soils with high shrinkage capacity more macropores are generated in the soil presenting a smaller proportional shrinkage slope. (C) 2015 Elsevier B.V. All rights reserved.

Feeding behavior of large herbivores determines the composition of their dung and together with environmental factors the intensity of decomposition processes leading to the recycling of nutrients in tropical forests. Large herbivore dung and its decomposition has so far been characterized by stoichiometric analyses of elements such as C and N. The objective of our study was to examine the suitability of biomarker analyses and analytical pyrolysis to infer large herbivore feeding behavior and the decomposition of their dung in different environments. Our conceptual approach included exposure of fresh dung of a grazing ruminant (gaur, Bos gaurus) and a non-ruminant mixed-feeder (the Asian elephant, Elephas maximus) in two tropical forest types (dry and moist) and analysis of dung biochemical composition in two seasons (dry and wet). To this end we characterized the dungs’ lignin and carbohydrate (sugar) signatures and pyrolysis products before and after 28 days of exposure. Our results showed that stoichiometric as well as biomarker analyses were able to differentiate gaur and elephant dung independent of season and forest type, while analytical pyrolysis products did not differ between dung types. The lignin signature of fresh dung additionally indicated the forage preference of animals in different forest types and seasons. During decomposition, C and N contents decreased and the chemical composition of both dung types converged. The lignin signature of dung at the end of the experiment showed higher lignin decomposition in moist forest and wet season than dry forest and dry season. We conclude that detailed biochemical analyses can provide deeper insights into the main controls of large herbivore dung and its decomposition in tropical forests than stoichiometric analysis. In particular lignin may be a suitable indicator to investigate large herbivore feeding behavior and the environmental conditions of their habitat.