Physico-chemical typology of the biogenic structures of termites and earthworms: a comparative analysis

A comparative analysis of 14 physico-chemical and organic parameters was conducted on three types of biogenic structures: earthworm casts and crop sheetings built by two fungus-growing termites (Ancistrotermes guineensis and Odontotermes nilensis) and compared to the neighbouring soil in a mango orchard in the Thiès region of Senegal. A principal component analysis shows clearly that the biogenic structures were differentiated from the neigbhouring soils in their content of organic components. The amino sugar contents of biogenic structures were 3-5 times higher than those measured in soil. In these structures, an increase in the contents of phenols and proteins was also observed. In contrast, their physical and chemical characteristics (texture, cationic exchanges capacity) were little different from those of the soil with the exception of their much lower water-retention capacity. Differences were also noted between the biogenic structures: the structures built by the two species of termite show more similarities with each other than with the casts. This result was confirmed by a similarity dendrogram which was used to graduate oppositions between samples. Casts were different from termite sheetings primarily in their C and N contents which were twice as high. Conversely, the contents of proteins in termite sheetings were higher than those measured in casts. Altogether, the results suggest that, in the biogenic structures, the organic content is stored and protected from mineralization.     

Use of RAPD markers for the study of microbial community similarity from termite mounds and tropical soils

In this study, we test the use of the RAPD (Random Amplified Polymorphic DNA) molecular markers as a way to estimate the similarity of the microbial communities in various termite mounds and soils. In tropical ecosystems, termite activities induce changes in the chemical and physical properties of soil. The question then arises as to whether or not termites affect the presence of natural microbial communities. Successful 16S rDNA amplifications provided evidence of the occurrence of bacterial DNA in termite constructions including both soil feeder and fungus grower materials. A phenetic dendrogram using the similarity distance calculated from pairwise data including 88 polymorphic RAPD markers was reconstructed and bootstrap scores mapped. The microbial communities of the mounds of the four soil-feeding termites were clustered in the same clade, while those of the mounds of the fungus-growing species were distinct like those of control soils. Microbial changes in nests result from termite building behavior, depending on whether they include feces in their constructions for soil-feeders or use saliva as particle cement for fungus-growers. It is argued that RAPDs are useful markers to detect differences in microbial community structure not only between termitaries and control soils but also between mounds of soil-feeders.     

Properties and functional impact of termite sheetings

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.     

Functional complement of biogenic structures produced by earthworms, termites and ants in the neotropical savannas

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, α-glucosidase, β-glucosidase, β-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.     

Consistent effects of eastern subterranean termites (Reticulitermes flavipes) on properties of a temperate forest soil

Termites inhabit a large portion of land covered by temperate forests. Climate warming and urbanization will likely extend their range and increase their densities in these ecosystems but, compared to their tropical counterparts, little is known about their effects on soil properties and processes. If temperate termites have the strong ecosystem engineering effects of tropical termites, then knowledge of their ecology and impacts will be vital for predicting how temperate systems respond to environmental change. We investigated how feeding and tunneling by the eastern subterranean termite, Reticulitermes flavipes, affected wood decomposition and soil properties under decaying wood. Twelve laboratory microcosms filled with mineral soil and with wood blocks of four common temperate tree species, received R. flavipes soldiers and workers at field densities, with an additional five termite-free microcosms serving as controls. After 25 weeks, the effects of termites on wood mass loss, and on carbon and nitrogen dynamics, differed across tree species, yet their effects on soil properties were consistent regardless of wood type. Microbially-available carbon in soil was 20% higher with termites and soil moisture content 20% lower. Soil pH was more acid with termites and their effects on soil microbial biomass were positive but non-significant. These soil responses were consistent regardless of the wood species, suggesting that termite effects on soil are dictated largely by their activity within the soil matrix and not by their feeding rate on specific wood substrates. These results are among the first to quantify the effects of temperate forest termite activity on soil properties, demonstrating the potential for these termites to shape biogeochemical cycling and plant communities through their alteration of the soil environment.     

Two-year field study shows little evidence that PPO-transgenic rice affects the structure of soil microbial communities

There is global concern about the environmental consequences associated with transgenic crops. Their effects on the soil ecosystem are of special interest when assessing ecological safety and integrity. Although many efforts have been made to develop crops genetically modified to have resistance to protoporphyrin oxidase (PPO)-inhibiting herbicides, little is known about their influence on soil microbial communities. We conducted a 2-year field study and an analysis via terminal restriction fragment length polymorphism (T-RFLP) to assess the impacts of PPO-transgenic rice on bacterial and fungal communities. In the first year we sampled the rhizosphere and surrounding bulk soil, while in the second year we sampled rhizosphere soil only. No differences were observed in the diversity indices and community composition of microbial communities between transgenic rice and its parental non-transgenic counterpart (cultivar Dongjin). Instead, community variation was strongly dependent on growth stage and year. Therefore, we observed no adverse effects by these crops of modified rice on the microbial community composition in paddy soils.     

Incidence of fungus-growing termites (Isoptera, Macrotermitinae) on the structure of soil microbial communities

The aim of this study was to investigate the impact of subterranean fungus-growing termites on the structure of soil microorganism communities. We tested whether termites significantly modify the abundance and structure of microbial communities within their below-ground nests (fungus-comb chambers) and whether these effects are species-specific.The investigations were carried out in a humid savanna reserve with material collected from the fungus-comb chamber walls of two widespread species differing in the mode of nest construction. Ancistrotermes builds diffuse and ephemeral nests while chambers of Odontotermes are mostly concentrated and occupy the same area for a comparatively much longer period of time then creating lenticular mounds. The soil properties (pH, texture and C, N content) and the microbial biomass were analysed and automated rRNA intergenic spacer analysis (ARISA) was used to characterise bacterial (B-ARISA) and fungal (F-ARISA) communities. Our results illustrate that the nest structures created by termites offer a diverse range of physical and chemical environments that differ strongly from those present in the general soil mass. Odontotermes had strong effects on microbial properties at the scale of the fungus-comb chamber and at the scale of the lenticular mound. In the fungus-comb chambers, the microbial biomass is not affected by termites but the structure of microbial community is different from that in the control open savanna soil. In the lenticular mound, the microbial biomass is higher and the structure of bacterial community is distinct than that in the fungus-comb chambers. Ancistrotermes also strongly influenced the structure of soil bacterial and fungal communities in the open savanna. However, we did not find any significant modification of bacterial and fungal community structures in the lenticular mound. The impact of fungus-growing termites is, therefore, species-specific and varies depending on the study site (open savanna vs. lenticular mound).     

Chemical,physical and micromorphological properties of termite mounds and adjacent soils along a toposequence in Zona da Mata,Minas Gerais State,Brazil

Little is known about the effects of neotropical mound-building termites in soil chemical and physical properties. The influence of soil termite activity on soil characteristics was studied by assessing chemical, physical and micromorphological properties of a toposequence of Latosols (Oxisols). Soil samples were collected from the walls and inner parts of termite mounds and also from adjacent soil. A high diversity of termite genera was found in the mounds along the toposequence, together with the inquiline termites and other soil-dwelling arthropods. Chemical analyses showed that pH and the contents of organic C and N, P, Ca and Mg were significantly higher in termite mounds compared with adjacent areas, with an inverse trend for Al content. Significant differences in pH and exchangeable Al were observed between soil and mound across the slopes. The mound density across the landscape was higher at the upper slope segment, followed by the hill top, middle slope and lower slope segments. Considering a lifespan of 30 years and dimensions of termite mounds found in the toposequence we conclude that the textural and chemical uniformity of Latosols may be increased, following the pedobiological turnover during mound building, with local rates varying from 2.1 to 7.5 m³ ha^− 1.     

Impact of subterranean fungus-growing termites (Isoptera, Macrotermitiane) on chosen soil properties in a West African savanna

Fungus-growing termites (Isoptera, Macrotermitinae) play an important role in tropical ecosystems in modifying soil physical properties. Most of the literature regarding the impact of termites on soil properties refers to termite epigeous mounds. In spite of their abundance and activity in African savannas, few studies deal with the properties of underground nest structures (fungus-comb chambers) built by subterranean Macrotermitinae termites. We tested whether these termites significantly modify the soil physico-chemical properties within their nests in a humid tropical savanna and whether these effects are different for two termite species with differing building behaviour. Termite-worked soil material was collected from fungus-comb chamber walls of two widespread species: Ancistrotermes cavithorax, which builds diffuse and ephemeral nests and Odontotermes nr pauperans, which most often builds concentrated and permanent nests for a comparatively much longer period of time. Neither species influenced soil pH but both significantly modified soil texture and C-N content in their nest structures. A strong impact on clay-particle size was also detected but no significant differences in clay mineralogy. Thus Odontotermes has a greater effect on soil properties, that could be explained by its building behaviour and the concentration in space of its nest units. Therefore, spatial pattern and life-span of fungus-comb chambers should be an important parameter to be considered in the functional role of subterranean Macrotermitinae termites in the savanna.     

Impacts of habitat disturbance on termites and soil water storage in a tropical Australian savanna

This study examines changes in the abundance and diversity of soil macroinvertebrate taxa and soil water storage across different disturbance treatments in a tropical savanna woodland in northern Australia. Nine plots representing three habitat disturbance treatments (uncleared savanna woodland; 25-year-old regrowth following past clearing; cleared areas) were sampled for macrofauna using soil pits in April 2003. Sub-surface soil moisture (0-0.4 m) was measured at 0.1 m intervals over the 2002/2003 wet season. Termites represented 55% of total individuals sampled. Abundance of soil macrofauna was greatest in uncleared plots and lowest in cleared plots, with the latter treatment also having the lowest taxon diversity. Mean abundances of termites, earthworms and ants were greatest in uncleared treatment plots. Five termite species from four genera were present, with Microcerotermes nervosus constituting 47% of termite species identified. Of the wood-, grass- and polyphagous-feeding termites present, wood-feeding species were restricted to uncleared treatment plots and grass-feeders to regrowth treatment plots. A shift in termite nesting habits from epigeal to hypogeal was observed from uncleared to cleared treatments. Soil water storage was lowest in the dry season and highest during the monsoon, and varied significantly across habitat disturbance treatments at the start and end of the wet season. Cleared plots were least effective in the capture of the first wet season rains, and uncleared treatment plots showed the greatest capacity to retain soil water during the transition from wet to dry season. The negative effects of habitat disturbance on soil water storage may have been partially mediated by the observed changes in soil macrofauna, especially termites.     

Impact of wheat straw decomposition on successional patterns of soil microbial community structure

The dynamics of indigenous bacterial and fungal soil communities were followed throughout the decomposition of wheat straw residue. More precisely, such dynamics were investigated in the different soil zones under the influence of decomposing wheat straw residue (i.e. residues, soil adjacent to residue = detritusphere, and bulk soil). The genetic structures of bacterial and fungal communities were compared throughout the decomposition process long by applying B- and F-ARISA (for bacterial and fungal-automated ribosomal intergenic spacer analysis) to DNA extracts from these different zones. Residue decomposition induced significant changes in bacterial and fungal community dynamics with a magnitude of changes between the different soil zones ordered as followed: residue > detritusphere > bulk soil, confirming the spatial structuration of the sphere of residue influence to the 4-6 mm soil zone in contact with residue. Furthermore, significant differences in the structure of bacterial and fungal communities were apparent between the early (14 and 28 days) and late (from 56 to 168 days) stages of decomposition. These could be related to ecological attributes such as the succession of r- (copiotrophs) and K- (oligotrophs) strategists. Microbial diversity at the early (28 days) and late (168 days) stages of degradation was further analysed by a molecular inventory of 16S and 18S rDNA in DNA extracts from the residue zone. This confirmed the succession of different populations during residue decomposition. Fluorescent Pseudomonas spp. and Neurospora sp. were dominant in the early stage with subsequent stimulation of Actinobacteria and Deltaproteobacteria taxa, as well as Basidiomycota fungal taxa and Madurella spp. According to the ecological attributes of these populations, microbial succession on fresh organic residue incorporated in soil would be dominated by copiotrophs and r-strategists in the early stages, with oligotrophs (K-strategists) increasing in relative abundance as substrate quantity and/or quality declines over time.     

埃塞俄比亚罗毕高原含铬雏形土地区凋落物饲喂的白蚁(Macrotermes spp)的化学性质及其生化活动的研究

Termite(Macrotermes spp.) mounds are complex biological habitats originated by the termite activity and possessing peculiar physical, chemical and biochemical properties. In this study we examined the concentration of nutrients and the biochemical activity of abandoned soil and mounds colonized by termites of the genera Macrotermes located in the Borana District, Ethiopia. To elucidate the magnitude and persistence of the termite-induced effects, we also studied an abandoned mound, previously colonized by termites of the same genera formed on the same soil. Results confirmed that termite-colonized mounds are ‘hot spots' of nutrient concentration and microbial activity in tropical soils. This is due to the termite driven litter input and decomposition. The abandoned mounds showed higher microbial biomass and activity and displayed a nutrient redistribution and a greater microbial activity than the adjacent soils. These findings allowed us to hypothesize a model of nutrient cycling in colonized soils and a partition of the relative roles of termites and soil microorganisms in nutrient location and turnover in tropical soils. These results may be also useful for the optimal management of termite-colonized soils.     

How distinct are arbuscular mycorrhizal fungal communities associating with grapevines?

Grapevines form associations with arbuscular mycorrhizal (AM) fungi. These root-dwelling fungi have the potential to contribute to crop vigor, productivity, pathogen protection, and nutrient content in grapes. In this study the arbuscular mycorrhizal fungal communities of grapevines and the surrounding interrow and native vegetation are compared. We found over 40 different taxa associating with both vines and interrow vegetation, but these communities differed based on host plant identity. These differences were apparent even after accounting for differences in soil chemical properties and differences in host plant diversity between vinerows and interrows, indicating that Vitis preferentially interacts with a subset of the viticultural fungal community. Since AM fungal communities play a major role in grapevine health, our results suggest that host identity and the diversity of AM fungal hosts in a vineyard can have strong effects on arbuscular mycorrhizal fungi community structure. In this paper, we used high throughput sequencing of the large subunit rDNA to analyze the diversity of AM fungi growing in a vineyard.     

Termites promote soil carbon and nitrogen depletion: Results from an in situ macrofauna exclusion experiment,Peru

We present results from one of the first in situ soil termite exclusion experiments using translocated soil that was not colonised by termites prior to the experiment. Macrofauna were excluded or included using fine (0.3 mm) and coarse (5 mm) mesh, respectively. We found that termites were the most dominant macrofauna in the macrofauna-included samples throughout the sampling period. Additionally, C and N depletion rates were consistently higher in samples with macrofauna than without macrofauna despite the seasonal decline of termites at the start of the wet season. This suggests that the presence of termites in soil promotes C and N depletion that may be linked to the passage of soil through the termite gut and the affect termites have on bioturbation and nutrient distribution.     

Effects of termites on the physical and chemical properties of the acid sandy soils of southern Nigeria

Abstract

This study was aimed at characterizing the effects of the activity of termites of the genus Nasutitermes on the physico‐chemical properties of the acid sandy soils of southern Nigeria. Selected morphological properties of the termite mounds were measured in the field. Outside portions of the termite mound and surface (0–15 cm) soil were collected and analyzed for some physical and chemical properties. Results obtained showed a density of 112 mounds ha^‐1 with average height of 0.85 m. There were significantly higher proportions of clay, silt, and organic carbon, and higher pH, exchangeable potassium (K), calcium (Ca), magnesium (Mg), available phosphorus (P), effective cation exchange capacity and base saturation in the mounds of the Nasutitermes than in the surrounding topsoil. Mounds of Nasutitermes termites, if returned to the soil, could improve the properties of the soil in areas where termites occur in large numbers.     

The influence of tillage on the structure of rhizosphere and root-associated arbuscular mycorrhizal fungal communities

Soil environmental factors affect the structure of arbuscular mycorrhizal (AM) fungal communities present in soil. However, it is not understood to which degree management practices such as tillage lead to dissimilarities between intra- and extraradical AM fungal communities. This study aims to assess the influence of two different soil management practices (conventional tillage and no-till) on the diversity of AMF communities, both in rhizosphere soil and inside corn roots. We hypothesized that under no-till, roots are colonized as they grow through the undisturbed fungal mycelia left from the previous crop whereas under conventional tillage they are colonized by those propagules that survived disturbance and can re-establish in their new relocated and mixed environment. We predicted that the degree of similarity of AM fungal communities inside versus outside the roots would be greater under no-till than under tillage. Using terminal restriction fragment length polymorphism (T-RFLP) and denaturing gradient gel electrophoresis we observed a different AM fungal community present in roots under no-till than under conventional tillage. Moreover, the communities present in the rhizosphere soil were different than in the roots of the corn plants. These results suggest that soil management does alter the diversity of AM fungal communities associated with corn roots and that plants influence the structure of the AMF community colonizing their roots. Sequencing results indicated that the majority of AMF species found in this agricultural soil was Glomus spp. However, further work is required to determine the extent to which AM fungal genotypic alterations by soil management influences competitive relationships.     

High performance liquid chromatography studies on the polysaccharides in the walls of the mounds of two species of termite in Senegal,Cubitermes oculatus and Macrotermes subhyalinus: their origin and contribution to structural stability

 The origin, nature and quantity of polysaccharides in the walls of the epigeal mounds of a species of soil-feeding termite, Cubitermes oculatus, and a fungus-growing termite, Macrotermes subhyalinus, found in Senegal, and of soil not considered to be under the influence of termites, were studied to obtain a clearer picture of the structural stability of these materials. The compounds were extractedand analysed by high performance liquid chromatography. We found that the walls of mounds made by soil-feeding species were very rich in sugars soluble in aqueous acid or hot water. Most of the sugars originated from cellulose and hemicellulose, and only a small proportion from microorganisms. There were also significant amounts of stachyose in the mound walls and in the reference soil. This sugar was probably formed by the surrounding vegetation, which was mainly leguminous crops. Comparison of the mineral and organic-mineral particle sizes of samples confirmed that the walls of soil-feeding termite mounds where there is the greatest redistribution of clay have the best aggregating capacity. The results therefore show that the polysaccharides in mound walls of soil-feeding termites are mostly of plant origin. Their influence on the stability of these structure is discussed. The walls of fungus-growing termite mounds contain little organic matter and hence low levels of polysaccharides, which are mainly of plant origin. Received: 19 July 1999     

Effect of gut transit and mound deposit on soil organic matter transformations in the soil feeding termite: A review

Even if termites are often considered as a pest due to the damage they cause to agriculture and architecture, they contribute to the soil humification process in the tropics. This impact on the soil organic matter humification process is due to the most important feeding habit in terms of species diversity, the soil feeding termites (∼1 200 species). Unlike other termites, their diet is not based on lignocellulosic plant degradation, but on the consumption of the mineral-containing horizons for the acquisition of nutrients. They are mostly distributed in humid forest or savannah equatorial zone. High structure and compartment with steep radial and axial gradients of O₂, H₂ and pH characterize their gut and create a patchy biotope. Furthermore, the humic compounds ingested are submitted, during a sequential transit, to different chemical (alkaline hydrolysis) and microbial degradation processes (fermentation, anaerobic respiration and mineralization). During this gut transit, the soil organic matter is strongly modified in terms of nature (organic matter concentration, fulvic and humic acid ratio) and organization (formation of organo-mineral complexes with clay). The soil organic matter ingested is further included as faeces in the nest and the galleries which, as a whole, constitutes the termitosphere. Compared to the control soil, the soil organic matter in the termitosphere is more stable and protected from the intense mineralization, which occurs in the tropics. These shifts of the organic matter into long turnover pool generated by the termite gut transit and deposition in the termitosphere indicate that besides the earthworm, the soil feeding termite has a positive impact on the overall organic matter cycling in the tropics.     

Abundance of biogenic structures of earthworms and termites in a mango orchard

A comparative study of the spatial distributions and the quantity of biogenic structures produced by earthworms and termites (Odontotermes nilensis and Ancistrotermes guineensis) has been conducted in a mango orchard at Thiès (Senegal).This study showed that surface biogenic structures may represent a large amount of modified soil (up to 536.5 g m⁻²) which vary depending upon the seasons and the species. Whilst the quantity of casts was independent on the season (178.6 g m⁻²), O. nilensis sheetings fluctuated with the seasons. In addition, we show that the spatial organisation of surface biogenic structures fluctuates with seasons. It displays patches ranging from 5 to 15 m. There is a link between the distribution of earthworm casts and the vegetation. In addition, spatial distribution was also linked to the biology of constructing species. We observed that the A. guineensis’ filling structures were mainly located under the mango trees during the dry season where the stems and the brushwoods were abundant. It appears that the spatio-temporal distribution of the biogenic structures under study depended upon two main factors: season and vegetation. However, depending upon the biology of the engineer, these two factors influenced the spatial distribution of structures in different ways.     

Ectomycorrhizal and Saprotrophic Fungal Communities Vary Across mm-Scale Soil Microsites Differing in Phosphatase Activity

To understand nutrient cycling in soils, soil processes and microorganisms need be better characterized. To determine whether specific trophic groups of fungi are associated with soil enzyme activity, we used soil imprinting to guide mm-scale sampling from microsites with high and low phosphatase activities in birch/Douglas-fir stands. Study 1 involved sampling one root window per site at 12 sites of different ages (stands); study 2 was conducted at one of the stem-exclusion stands, at which 5 root windows had been installed. Total fungal and ectomycorrhizal (EM) fungal terminal-restriction fragment length polymorphism (TRFLP) fingerprints differed between high-and low-phosphatase activity microsites at 8 of 12 root windows across 12 sites. Where differences were detected, fewer EM fungi were detected in high-than low-phosphatase activity microsites. Using 5 root windows at one site, next-generation sequencing detected similar fungal communities across microsites, but the ratio of saprotrophic to EM fungal reads was higher in high-phosphatase activity microsites in the two windows that had low EM fungal richness. In windows with differences in fungal communities, both studies indicated that EM fungi were less successful than saprotrophic fungi in colonizing fine-scale, organic matter-rich microsites. Fine-scale sampling linked with in situ detection of enzyme activity revealed relationships between soil fungal communities and phosphatase activity that could not be observed at the scales employed by conventional approaches, thereby contributing to the understanding of fine-scale phosphorus cycling in forest soils.