Soil Macroinvertebrates Research Articles

Combined effects of elevated temperatures and reduced leaf litter quality on the life‐history parameters of a saprophagous macroarthropod

AbstractBecause soil macroinvertebrates strongly modify decomposition processes, it is important to know how their abundance will respond to global change. We investigated in laboratory microcosms, the effects of elevated temperatures and reduced leaf litter quality on the life‐history traits of a saprophagous macroarthropod (development time, growth, survival and reproduction). Millipedes (Polydesmus angustus) from an Atlantic temperate forest were reared throughout their life cycle (≥16 months) under two temperature regimes differing on average by 3.3 °C; in a factorial design, they were fed either on Atlantic leaf litter or on Mediterranean leaf litter with a higher C : N ratio; humidity was consistently high. The components of the population growth rate (r) were affected positively by the temperature rise and negatively by the switch from Atlantic to Mediterranean leaf litter. When both treatments were combined, litter effects offset temperature effects. These results show that the short‐term response of saprophagous macroarthropods to warming is positive but depends on the availability of high‐quality litter, which is difficult to predict in the global change context. In a parallel experiment, conspecific millipedes from a Mediterranean population, which have evolved for a long time in a warmer climate and on poor‐quality litter, were reared at elevated temperatures on Mediterranean leaf litter. All components ofrwere higher than in the Atlantic population under the same conditions. This suggests that in the longer term, macroarthropods can overcome detrimental trophic interactions. Based on our study and the literature, we conclude that for decades the positive effects of warming on saprophagous macrofauna should exceed the negative effects of changes in litter quality. The abundance of those organisms in temperate forests could increase, which is confirmed by latitudinal patterns in Europe. Studies aimed at predicting the impacts of global change on decomposition will need to consider interactions with soil macroinvertebrates.

Current and Potential Roles of Soil Macroinvertebrates (Earthworms, Millipedes, and Isopods) in Ecological Restoration

AbstractSoil macroinvertebrates have a considerable impact on soil functions important to the restoration process, such as decomposition; yet, soil organisms have received relatively little attention in restoration ecology in terms of their applicability as agents of restoration. Here, we review how large obligate detritivores (earthworms, millipedes, and isopods) have been used to accomplish restoration goals, assess restoration progress, and function as bioindicators. Patterns of detritivore community succession and how these communities are themselves restored during restoration of perturbed ecosystems are also discussed. We conclude with a discussion of increased utilization of these taxa in future and ongoing restoration projects as well as the outreach activities that should be associated with use of these organisms.

Divergent biogeography of native and introduced soil macroinvertebrates in North America north of Mexico

ABSTRACTTo improve understanding of the biogeographical consequences of species introduction, we examined whether introduced soil macroinvertebrates differ from natives in the relationship between species richness and key environmental predictors, and whether such differences affect the relationship between native and introduced species richness. For North America north of Mexico, we summarized jurisdiction occurrence data for seven macroinvertebrate taxa with strong influences on soil biodiversity or processes. We analysed the relationships of native and introduced species richness to each other using linear regression; to latitude using Gaussian regressions; and, using the residuals of the richness–latitude regressions, to distance from coasts, human population density, and human population size using regression and correlation. We found weak to strong positive relationships between native and introduced species richness. This variation was related to divergent relationships of native and introduced species with latitude, human population density, and distance from coasts. Native species richness declined with increasing latitude for all taxa, as did introduced species richness for taxa with predominantly lower‐latitude origins (ants, termites, non‐lumbricid earthworms). In contrast, introduced species richness peaked at higher latitudes for four taxa of predominantly Palearctic origins (weevils, ground beetles, lumbricid earthworms, isopods). Partitioning introduced taxa within these groups based on region of origin, we found that Palearctic taxa were distributed at higher latitudes than non‐Palearctic taxa. Thus source region appears to strongly influence introduced species richness–latitude relationships. Compared to natives, introduced species exhibited more positive relationships with human population density and negative relationships with distance from coasts, but did not differ in relationships with human population size. Thus coastal, densely populated regions are likely to have a higher proportion of introduced soil macroinvertebrate species. These differences between distribution of native and introduced species tend to weaken positive correlations between native and introduced species richness, especially for taxa dominated by Palearctic introductions.

Do feral house mice have an impact on invertebrate communities on sub-Antarctic Marion Island?

Abstract House mice (Mus domesticus L.) have been present on sub-Antarctic Marion Island since the early 1800s. Several authors have suggested that an increase in mice density as a result of a general warming trend in the sub-Antarctic climate from the 1960s has led to a decline in invertebrate biomass and abundance. These suggestions have been supported by the observation that the invertebrates of nearby mouse-free Prince Edward Island are apparently larger and more numerous than on Marion. Our experiment was designed to determine whether mice have a direct effect on invertebrate abundance, biomass and community structure, or an effect on the vegetation community and thus potentially an indirect effect on invertebrates. We constructed five wire-mesh mouse-free exclosures in one habitat type on Marion Island and recorded both the soil macro-invertebrate community and the vegetation inside and outside each of the exclosures before the start of the experiment in 1996 and twice thereafter (1998 and 2000). Mice had no significant effect on any of the eight prey groups' abundance or biomass, or on community structure (diversity and composition). Four of the prey groups changed significantly over time in either biomass or abundance, independent of the presence of mice. Our results, which may have been affected by generally low statistical power, suggest that factors other than mice had a larger impact on invertebrates than mice alone.

Do boundaries of soil animal and plant communities coincide? A case study of a Mediterranean forest in Russia

We studied the relationship between plant and soil animal communities by geostatistical analysis in a piedmont forest close to Novorossiysk (Southern Russia). Vegetation on the slope of a hill was an oak-ash-hornbeam forest, while the vegetation on the foot of the hill was a maple-ash-hornbeam forest. Two plots were studied each including both slope and foot habitats. On every plot samples collected formed a grid of 10 × 5 units with a 5 m distance between them. Soil macroinvertebrates were hand-sorted from the samples, and several soil parameters (soil, pebble, and litter mass, soil moisture) were measured. The analysis did not reveal coincidence between the boundaries of plant and soil animal communities on the bend of the hill. Soil animal communities of the plots were dominated by woodlice, diplopods, and insect larvae, reaching an abundance of 680–990 individuals m − 2 throughout the plots. Number of taxonomic groups per sample and overall animal abundance in the bend were the highest in both plots, whilst these parameters on the slope were the lowest. Variograms and maps of spatial distribution indicated that the boundary between soil animal communities was situated further up on the slope than the vegetation boundary. The size of the animal community was smaller than the size of plots sampled, what probably explained the lack of coincidence between the boundaries. There was a significant correlation between distribution of litter mass and parameters of soil animal communities, which was modulated by depth of soil layer and soil moisture. Soil parameters were more important for explaining boundaries between soil animal communities than plant communities in the forest considered.

Evaluating the efficiency of sampling methods in assessing soil macrofauna communities in arable systems

The soil fauna is often a neglected group in many large-scale studies of farmland biodiversity due to difficulties in extracting organisms efficiently from the soil. This study assesses the relative efficiency of the simple and cheap sampling method of handsorting against Berlese–Tullgren funnel and Winkler apparatus extraction. Soil cores were taken from grassy arable field margins and wheat fields in Cambridgeshire, UK, and the efficiencies of the three methods in assessing the abundances and species densities of soil macroinvertebrates were compared. Handsorting in most cases was as efficient at extracting the majority of the soil macrofauna as the Berlese–Tullgren funnel and Winkler bag methods, although it underestimated the species densities of the woodlice and adult beetles. There were no obvious biases among the three methods for the particular vegetation types sampled and no significant differences in the size distributions of the earthworms and beetles. Proportionally fewer damaged earthworms were recorded in larger (25 × 25 cm) soil cores when compared with smaller ones (15 × 15 cm). Handsorting has many benefits, including targeted extraction, minimum disturbance to the habitat and shorter sampling periods and may be the most appropriate method for studies of farmland biodiversity when a high number of soil cores need to be sampled.

Transformation and mineralization of soil organic nitrogen by the humivorous larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

We studied transformation and mineralization of nitrogenous soil polymers by the humivorous larva of the scarabaeid beetle Pachnoda ephippiata, using 14C-labeled peptides, peptidoglycan, and chitin, both native and stabilized by co-polymerization with synthetic humic acids. The results indicated that these materials were solubilized mainly in the alkaline midgut. The solubilization rate of peptides to TCA-soluble products was higher than those of peptidoglycan and chitin. Solubilization rates were lower when the polymers were stabilized in humic acids. Incubation of soil with midgut fluid released amino acids, which explains the high in vivo concentrations of amino acids observed in the midgut fluid. The large amounts of \( {\text{NH}}^{ + }_{4} \) in the fresh fecal pellets indicated that at least 1.7% of the total nitrogen (7% of the acid-hydrolyzable peptides) in the ingested soil was mineralized during gut passage; also the amount of soluble protein and the solubility of humic substances increased. The combined evidence supports the hypothesis that not only microbial biomass but also the nitrogen-rich components of humus are important dietary components for humivorous insects, and that feeding activities of soil macroinvertebrates strongly impact transformation and mineralization of soil organic matter.

The feeding ecology of elaterid larvae in central European arable land: New perspectives based on naturally occurring stable isotopes

To understand soil food webs, empirically generated data on the trophic connections and the feeding ecology of the major below-ground animal taxa are needed. Here we used stable isotope analysis to assess the trophic ecology of wireworms, the larvae of click beetles, in Central European arable land. Wireworms are amongst the major soil macroinvertebrates and are of practical importance in arable soils. Besides feeding on crops, they are thought to feed on weeds, soil organic matter (SOM), and even animal prey, but their feeding ecology is poorly studied under natural conditions. Elaterid larvae and their putative feeding substrates—plant roots, SOM, and litter—were sampled at 17 locations in Austria, Germany, and Italy and their isotope ratios of carbon ( 12C/ 13C) and nitrogen ( 14N/ 15N) measured to determine the wireworms’ trophic level, the importance of SOM and weeds within the diet of Agriotes larvae, as well as the individual diet variation in Agriotes obscurus larvae. δ 15N signatures suggested that Agriotes larvae are predominately herbivorous, whereas the other wireworm species primarily fed on animal prey. In contrast to SOM, weeds were readily eaten by Agriotes larvae: their dietary contribution ranged between 28% and 67% in weedy maize fields. Most A. obscurus larvae fed on a mixed diet of weeds and maize, although ∼15% of the larvae fed primarily on one of the two food sources only. δ 15N signatures indicated that ∼10% of the “herbivorous” A. obscurus larvae fed primarily on animal prey, revealing high intraspecific trophic plasticity in these soil insects. Wireworm feeding behaviour is apparently complex at the individual level: the population consists of types A and B generalists, a phenomenon which needs further assessment.

Short‐term effects of low intensity fire on soil macroinvertebrate assemblages in different vegetation patch types in an Australian tropical savanna

Abstract Early dry season fires are a common land management regime employed across the tropical savannas of northern Australia. The rationale is that this reduces fuel loads and so reduces fire risk in the latter part of the dry season. Despite the acceptance of fire as a major management tool the ecological effects of fire remain uncertain. Vegetation patches and their associated macroinvertebrates play a critical role in the capture and recycling of water and nutrients. The aim of this study was to examine the responses of soil macroinvertebrates, within different types of vegetation patches, to early dry season fires in tropical savanna woodland in northern Australia. The abundance of major macroinvertebrate taxa and functional groups, and taxon richness were quantified in three vegetation patch types 2 weeks before and 2 weeks after burning. Termites dominated the soil macroinvertebrate assemblage sampled. Fire led to significant decreases in ant and spider abundances and overall taxon richness. Functional group analyses showed significant overall declines in the abundances of macropredators and litter transformers. There were also interactions between fire and patch type; in tree patches, fire significantly reduced total macroinvertebrate abundance, as well as the abundance of termites and ecosystem engineers. These changes in soil macroinvertebrates will potentially influence patch functionality, with important implications for soil processes and landscape health.

Effects of ground cover (straw and compost) on the abundance of natural enemies and soil macro invertebrates in vineyards

Abstract1 Herbicides are commonly applied under grapevines in Australia to remove weeds and thereby to avoid water loss through transpiration.2 Interest in sustainability promotes a reduction in chemical inputs, including herbicides, leading to trials with surface mulches to suppress weeds.3 Surface mulches may also influence the abundance of a range of invertebrates. Potentially, an increase in natural enemies will contribute to pest control and encourage a reduction in pesticide application.4 We used three trapping methods and direct soil sampling to assess invertebrates at ground level, in the canopy and in the soil to determine the influence of mulch on natural enemies, potential pests and soil macroinvertebrates, including earthworms.5 Collections sorted to family demonstrated that the addition of straw or compost mulches increased natural enemies collected with pitfall traps and soil organisms. However, there was no clear indication of the overall superiority of either mulch.6 Abundance of ground beetles, parasitoid Hymenoptera and spiders collected with pitfall traps were increased by the addition of mulches. In the canopy, predatory and parasitic Diptera and predatory Hemiptera increased after mulching.7 Earthworms collected by hand sorting soil increased with straw mulching.8 No influence on pests was detected. Although Lepidoptera and Sigmurethra, collected in pitfall traps, increased with straw mulching, neither included pest species.9 The results are discussed with reference to the potential economic impact of mulches.

Soil macroinvertebrate fauna of a Mediterranean arid system: Composition and temporal changes in the assemblage

Temporal variability is a key factor to understand the structure of belowground communities. Seasonal and annual variations are especially relevant in unpredictable desert ecosystems, where macroinvertebrates are poorly known, despite constituting an important group of soil organisms. In the present study, we analyse the composition and temporal (seasonal and annual) variations of soil macroinvertebrates in an arid area of southern Spain. During two years, macroinvertebrates were sampled in litter and belowground levels by means of soil cores. Results show that the assemblage was dominated by arthropods, especially Formicidae and Coleoptera. The assemblage differed between litter and belowground levels. In litter, detritivores dominated the community, while belowground fauna showed a similar proportion of detritivores and herbivores and a low percentage of predators. Litter and belowground assemblages showed seasonal variations in richness, abundance, biomass and composition, although variations were more marked in litter than belowground. Patterns of seasonal variation also differed between the two study years for both litter and belowground invertebrates. The seasonal and annual variability of the assemblage has potentially important implications for community dynamics in the study system, since the changes in species composition and trophic structure of soil invertebrate assemblages may affect species interactions and food web dynamics over time. Therefore, integrating temporal variability is likely to be crucial to understand soil community dynamics and food webs, especially in heterogeneous, variable systems as deserts.

Effects of summer rainfall manipulations on the abundance and vertical distribution of herbivorous soil macro-invertebrates

Soil invertebrate communities are likely to be highly vulnerable to low soil moisture, caused by a reduction in summer rainfall which is predicted for some regions under current climate change scenarios. However, the effects of changes in summer rainfall on soil invertebrate assemblages have rarely been tested experimentally. In this study, samples were taken in 2003 and 2004 from a long-running field experiment, to investigate the impact of 10 years of experimental summer drought and increased summer rainfall manipulations on the soil fauna of a calcareous grassland. Summer drought altered the soil invertebrate assemblage in the autumn, immediately following treatment application, but by the following spring treatment effects were no longer apparent. The two most common root herbivore species responded differently to the summer rainfall manipulations. Larvae of the dominant root-chewing species, Agriotes lineatus, were more numerous under enhanced rainfall in both the spring and autumn. In contrast, abundance of the Coccoidea Lecanopsis formicarum was unaffected by the rainfall manipulations. The responses of root herbivores to an increased incidence of summer droughts are therefore likely to vary, depending on their feeding strategy and life history.

This ped is my ped: Visual separation and near infrared spectra allow determination of the origins of soil macroaggregates

Summary Macroaggregation is a highly dynamic attribute of soils that is claimed to have a significant impact on their ability to store C and conserve nutrients. A major obstacle to the description and modelling of macroaggregate dynamics, and of the associated processes, is an almost complete ignorance of the real origin of the different types of aggregates found in soils, their turnover times and positions in the soil matrix. We present here a general methodological approach in which the origin of aggregates separated according to visual criteria could be determined by comparing their specific organic matter signatures assessed by Near Infrared Spectrometry (NIRS) to signatures of biogenic structures produced by soil ecosystem engineers (invertebrates and roots) living in the same soil. Macroaggregates and other soil components were separated visually from samples taken at 61 locations regularly distributed across a watershed in Nicaragua and representing crops, pastures, forests, coffee plantations and fallows. Coinertia analyses among soil macroinvertebrate communities and the matrix of soil morphological variables showed highly significant relationships. In Amazonian forest patches and pastures from the state of Para in Brazil, 75 different types of biogenic structures were collected at the soil surface and on tree trunks, and analysed by the NIRS spectral method. Significant differences among the different types of structures allowed grouping according to their broad phylogenetic origin with large interspecifc differences. In a field experiment conducted at the same site, soils previously under pastures were planted in 16 possible combinations of four plant species, in a fully randomized design replicated three times in different sites. Surface casts of the earthworm species Andiodrilus pachoensis and soil macroaggregates separated by our visual technique had significantly different spectral signatures depending on the location of the plot and the composition of plant cover. However, the comparison of NIRS signatures of soil macroaggregates and casts suggested that Andiodrilus pachoensis was not responsible for the production of the biogenic aggregates that comprised a large proportion on the soil volume in this soil.

Introduced slugs and indigenous caterpillars as facilitators of carbon and nutrient mineralisation on a sub-Antarctic island

Indigenous soil macroinvertebrates (moth larvae, weevil larvae, earthworms) are cardinal agents of nutrient release from litter on sub-Antarctic Marion Island (47°S, 38°′E). Their populations are threatened through predation by introduced house mice, which do not prey on an introduced slug Deroceras panormitanum. A microcosm study was carried out to explore whether slugs affect rates of carbon and inorganic nutrient mineralisation from plant litter differently to an indigenous caterpillar (larva of a flightless moth Pringelophaga marioni). Caterpillars stimulated N, Ca, Mg and K mineralisation from plant litter two to five times more than slugs did, whereas the two invertebrate types stimulated C and P mineralisation to the same degree. Consequently, ratios of C:N and N:P released from the litter were different for slugs and caterpillars. Such differences might affect peat nutrient quality and ultimately the peat accumulation-decomposition balance, an important driver of ecological succession. This suggests that slugs cannot simply replace caterpillars without consequences for ecosystem structure and functioning on the island.

Beech leaf degradation in laboratory experiments: Effects of eight detritivorous invertebrate species

This work addresses the impact of eight detritivorous species of soil macro-invertebrates (three millipedes, two woodlice and three earthworms) on short-term carbon mineralization and mechanical breakdown of beech leaves. The production rate, size class distribution and OM content of invertebrate faeces were also measured. Hierarchical clustering (HC) and multivariate analysis were performed to find relevant functional groups among the species studied. Our results identified three groups of macro-invertebrates on the basis of their impacts on beach leaf degradation (hierarchical clustering): (1) invertebrates that produce fresh faeces with high N contents compared with other species (i.e. polydesmidae and a single species of lumbricidae); (2) other lumbricidae that fragment litter into fine particles in their faeces and actively stimulate CO 2 release; (3) other arthropods that fragment litter into coarse particles and have weak impacts on OM mineralization. These groups over-ride taxonomy, and are proposed as a tentative functional classification of litter dwelling invertebrates. On the other hand, an idiosyncratic impact of species was observed in each group, highlighting how much empirical data are still needed to propose a robust functional classification of litter invertebrates.

Successional changes in soil, litter and macroinvertebrate parameters following selective logging in a Mexican Cloud Forest

The environmental and vegetation shifts associated with logging disturbance and secondary succession in Tropical Montane Cloud Forests have been studied in detail, however little is known about the consequences that these changes have for the soil system. The present study was undertaken to determine the impact of selective logging and subsequent secondary succession on soil microenvironmental conditions, leaf litter quality and quantity, soil nutrient concentration and soil and litter macroinvertebrate community composition. The study was carried out in three successional chronosequences, two recently logged sites and two pristine tropical mountain cloud forest sites in Oaxaca, Mexico. Results showed that selective harvesting of Quercus spp. trees caused an increase in soil temperature of ca. 4 °C that is not completely reversed after 100 years of succession. During 100 years of secondary succession litter diversity increased and soil organic matter accumulated (16.4% increase in total C). The availability of cations (Ca, Mg, Na, and K) in the topsoil decreased by more than 50% as a result of logging, and only Mg increased again between 75 and 100 years after disturbance. Pristine cloud forests sustain a diverse litter and soil macroinvertebrate community, but its composition and diversity was negatively affected by logging. The effect of Quercus harvesting activities on the litter community was apparent within 2 months of disturbance (total abundance declined by ca. 65%, higher taxa richness by ca. 10% and diversity by ca. 35%). For the soil community there was a time-lag in the effect of logging. Two months after disturbance there was no significant effect on the soil community but 15 years after abandonment, total macroinvertebrate abundance in the soil was ca. 80% lower and higher taxa richness ca. 30% lower compared to undisturbed sites. Full recovery of the macroinvertebrate community composition appeared to take more than 100 years both in the litter and soil. Reduced abundances of Coleoptera and Enchytraeidae were apparent even after 100 years of succession. The endemic earthworm Ramiellona wilsoni was found almost exclusively in the pristine forests and therefore its abundance could be used as a sensitive indicator of disturbance in these forests.

Long-term effect of a legume cover crop ( Mucuna pruriens var. utilis) on the communities of soil macrofauna and nematofauna, under maize cultivation, in southern Benin

In southern Benin like in other tropical areas, natural fallows, which were traditionally used in order to improve soil fertility, are no longer possible in a context of high population pressure. Many studies have underlined the advantages of legume cover crops to ensure the sustainability of plant productivity: increase in soil organic matter content, increase in crop yields, improvement of the water regime of soils, and decrease in runoff and erosion. Nevertheless the mechanisms responsible for these modifications are not completely understood. The characterisation of biological activity and diversity in a soil can help in understanding the dynamics of soil structure and the flux of nutrients. For this purpose, the density, diversity and functional composition of soil nematodes and soil macroinvertebrates were measured in different treatments under maize cultivation. The three treatments were: (1) a pure traditional maize crop without any fertilisation (T); (2) a maize crop with a mineral fertiliser (NPK); and (3) a maize crop inter-cropped with Mucuna pruriens var. utilis (M). Soil in plot M presented different biological properties when compared with T and NPK: higher macrofauna density (especially termites, earthworms, millipedes, centipedes) and biomass (especially earthworms and termites), higher density of facultative phytophagous, bacterial-feeding and predatory nematodes, and lower density of obligatory phytophagous ( Criconemella, Scutellonema and Meloidogyne) nematodes. The modification of the composition and activity of soil biota under Mucuna might partly explain the potential of Mucuna for soil restoration.

Spatial Patchiness of Litter, Nutrients and Macroinvertebrates during Secondary Succession in a Tropical Montane Cloud Forest in Mexico

We test the hypothesis that secondary succession in Tropical Montane Cloud Forest (TMCF) in Mexico is accompanied by an increase in the spatial structuring of litter resources, soil nutrient concentrations and the soil macroinvertebrate community at a within-plot scale (5–25 m). This increased spatial structuring is expected because secondary succession in these forests is associated with an increase in the diversity of trees that dominate the canopy. If each tree species generates a particular soil environment under its canopy, then under a diverse tree community, soil properties will be spatially very heterogeneous. Tree censuses and grid sampling were performed in four successional stages of a secondary chronosequence of TMCF. Variography was used to analyse spatial patterns in continuous variables such as nutrient concentrations, while Spatial Analysis by Distance Indices (SADIE) was applied to determine patchiness in the distribution of soil macroinvertebrate taxa. Secondary succession was found to be accompanied by the predicted increase in the spatial structuring of litter resources and the macroinvertebrate community at the within-plot scale. Spatial patterns in the macroinvertebrate community only became evident for all taxa in the oldest forest (100 years old). Patches with low Ca and Mg concentrations in early successional soils were associated with patches where pine litter was most abundant while those with low P concentrations in late successional stages were associated with patches where oak litter was most abundant. Results suggest that anthropogenic disturbance aboveground promotes a more homogeneous resource environment in the surface soil, which compared to older forests, sustains a less diverse and less spatially structured macroinvertebrate community.

Long-term land-use effects on soil invertebrate communities in Southern Piedmont soils, USA

Historically, a large percentage of land area in the Piedmont of the southeastern USA was under intensive agricultural management for the production of cotton. This intensive farming resulted in massive erosion, and general degradation of soil resources until insect pests and poor economic conditions forced large-scale abandonment of farmland around the 1930s. In subsequent decades, there have been four predominant land-uses in the region, and we sampled soil macroinvertebrates from three replicate sites of cultivated fields, grass-dominated fields, loblolly pine stands, and remnant hardwood stands for a period of 2 years, with the objective of examining soil invertebrate community composition in relation to these long-term land-uses. At each site we dug three or four soil pits that were 30 × 30 cm to a depth of 15 cm, and sorted the soil volume by hand for a time not more than 1 person h, collecting all invertebrates ~5 mm in length or larger. We recorded abundance data for all invertebrate taxa collected, and we calculated community indices including diversity, evenness, rank abundance and percent similarity in order to identify patterns of community assemblage within each land-use type. Results suggest that soils in hardwood stands support the most taxonomically diverse macroinvertebrate communities followed by pine stands, pastures, and cultivated fields in order of decreasing diversity. For earthworms, Diplocardia spp. (North American megascolecids) were most abundant in the hardwood stands, but sometimes made up a substantial fraction of the community in other land-uses; whereas lumbricid earthworms (primarily introduced Apporectodea spp.) were most abundant in the cultivated and pasture soils, or showed no consistent habitat preference (native Bimastos spp.). Scarab beetles (larvae and adults) were common in all four systems, but reached the highest densities in cultivated and grass sites. Carabid beetle larvae were collected most often from cultivated soils. Several taxa were collected either exclusively or predominantly from forested sites, including diplopods, chilopods, gastropods, and several taxa of Diptera. These results indicate that long-term soil disturbance and the attendant differences in vegetation structure have profoundly influenced the community composition of invertebrates in Southern Piedmont soils, and that more intense disturbance results in a less diverse invertebrate community composed of a few, frequently non-native, disturbance-tolerant taxa.

Nitrogen Mineralization, Ammonia Accumulation, and Emission of Gaseous NH3 by Soil-feeding Termites

There are numerous reports on the accumulation of ammonia in the mounds of soil-feeding termites. Here, we provided direct evidence for an effective mineralization of nitrogenous soil organic matter in the gut of Cubitermes spp., which gives rise to enormous ammonia concentrations in the intestinal tract. In Cubitermes ugandensis, the ammonia content of the nest material [24.5 μmol (g dry wt.)−1] was about 300-fold higher than that of the parent soil. Large amounts of ammonia were present throughout the intestinal tract, with lowest values in the extremely alkaline gut sections (pH >12) and highest values posterior hindgut [185 μmol (g dry wt.)−1]. Results obtained with other Cubitermes species were similar. Ammonia concentrations in the posterior hindgut of these humivorous species (up to 130 mM) are among the highest values ever reported for soil macroinvertebrates and are matched only by insects feeding on an extremely protein-rich diet (e.g., the sarcophageous larvae of blowflies). Volatilization of ammonia [about 10 nmol (g fresh wt.)−1 h−1], either directly by emission from the termite body or indirectly from their feces, led to NH3 concentrations in the nest atmosphere of C. ugandensis that were three orders of magnitude above the ambient background – a relative accumulation that is considerably higher than that observed with CH4 and CO2. Together with previous results, these observations document that through their feeding activity and due to the physicochemical and biochemical properties of their digestive system, soil-feeding termites effectively catalyze the transformation of refractory soil organic nitrogen to a plant-available form that is protected from leaching by adsorption to the nest soil. Nitrogen mineralization rates of soil-feeding termites may surpass those effected by tropical earthworms and should contribute significantly to nitrogen fluxes in tropical ecosystems.