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Habitat heterogeneity is an important driver of aboveground species diversity but few studies have investigated effects on soil communities. Trees shape their surrounding by both leaf litter and roots generating small scale heterogeneity and potentially governing community patterns of soil organisms. To assess the role of vegetation for the soil fauna, we studied whether tree species (Fagus sylvatica L., Acer pseudoplatanus L., Fraxinus excelsior L., Tilia cordata Mill.), markedly differing in leaf litter quality and root associated mycorrhizal symbionts, affect oribatid mite communities by shaping below- and aboveground resources and habitat complexity and availability. Oribatid mite abundance, species richness, community structure and the proportion of litter living and parthenogenetic individuals were analyzed and related to microbial biomass and the amount of remaining litter mass. Although leaf litter species with higher nutritional values decomposed considerably faster, microbial biomass only slightly differed between leaf litter species. Neither root species nor leaf litter species affected abundance, species richness or community structure of oribatid mites. However, root species had an effect on the proportion of parthenogenetic individuals with increased proportions in the presence of beech roots. Overall, the results suggest that identity and diversity of vegetation via leaf litter or roots are of minor importance for structuring oribatid mite communities of a temperate forest ecosystem.

The input of plant leaf litter has been assumed to be the most important resource for soil organisms of forest ecosystems, but there is increasing evidence that root-derived resources may be more important. By trenching roots of trees in deciduous and coniferous forests, we cut-off the input of root-derived resources and investigated the response of microorganisms using substrate-induced respiration and phospholipid fatty acid (PLFA) analysis. After one and three years, root trenching strongly decreased microbial biomass and concentrations of PLFAs by about 20%, but the microbial community structure was little affected and the effects were similar in deciduous and coniferous forests. However, the reduction in microbial biomass varied between regions and was more pronounced in forests on limestone soils (Hainich) than in those on sandy soils (Schorfheide). Trenching also reduced microbial biomass in the litter layer but only in the Hainich after one year, whereas fungal and bacterial marker PLFAs as well as the fungal-to-plant marker ratio in litter were reduced in the Schorfheide both after one and three years. The pronounced differences between forests of the two regions suggest that root-derived resources are more important in fueling soil microorganisms of base-rich forests characterized by mull humus than in forests poor in base cations characterized by moder soils. The reduction in microbial biomass and changes in microbial community characteristics in the litter layer suggests that litter microorganisms do not exclusively rely on resources from decomposing litter but also from roots, i.e. from resources based on labile recently fixed carbon. Our results suggest that both bacteria and fungi heavily depend on root-derived resources with both suffering to a similar extent to deprivation of these resources. Further, the results indicate that the community structure of microorganisms is remarkably resistant to changes in resource supply and adapts quickly to new conditions irrespective of tree species composition and forest management.

Land-use change is threatening biodiversity worldwide, affecting above and below ground animal communities by altering their trophic niches. However, shifts in trophic niches with changes in land use are little studied and this applies in particular to belowground animals. Oribatid mites are among the most abundant soil animals, involved in decomposition processes and nutrient cycling. We analyzed shifts in trophic niches of six soil-living oribatid mite species with the conversion of lowland secondary rainforest into plantation systems of different land-use intensity (jungle rubber, rubber and oil palm monoculture plantation) in two regions of southwest Sumatra, Indonesia. We measured stable isotope ratios (13C/12C and 15N/14N) of single oribatid mite individuals and calculated shifts in stable isotope niches with changes in land use. Significant changes in stable isotope ratios in three of the six studied oribatid mite species indicated that these species shift their trophic niches with changes in land use. The trophic shift was either due to changes in trophic level (δ15N values), to changes in the use of basal resources (δ13C values) or to changes in both. The trophic shift generally was most pronounced between more natural systems (rainforest and jungle rubber) on one side and monoculture plantations systems (rubber and oil palm plantations) on the other, reflecting that the shifts were related to land-use intensity. Although trophic niches of the other three studied species did not differ significantly between land-use systems they followed a similar trend. Overall, the results suggest that colonization of very different ecosystems such as rainforest and intensively managed monoculture plantations by oribatid mite species likely is related to their ability to shift their trophic niches, i.e. to trophic plasticity.

Global change processes affect seasonal dynamics of salt marshes and thereby their plant and animal communities. However, these changes have been little investigated for microarthropod communities. We studied the effect of seasonality and changes in sea level on oribatid mites in the natural salt marsh and on artificial islands in the back-barrier environment of the island Spiekeroog (Wadden Sea, Germany). Three zones of the artificial islands were filled with transplanted sods from the lower salt marsh zone and thereby exposed to three different inundation frequencies. We hypothesized that oribatid mite communities will differ along the natural salt marsh vegetation zones [upper salt marsh (USM), lower salt marsh (LSM), pioneer zone (PZ)], which are influenced by different tidal regimes. Accordingly, total oribatid mite densities declined from the USM and LSM to the PZ. Similarly, oribatid mite species compositions changed along the salt marsh transect and also responded to variations in inundation frequency in LSM on artificial islands with typical species of the USM, LSM and PZ being Multioppia neglecta (USM), Hermannia pulchella (LSM), Zachvatkinibates quadrivertex (LSM, PZ) and Ameronothrus schneideri (LSM, PZ). Oribatid mite density in the salt marsh and on the artificial islands was at a maximum in winter and spring; this was due in part to high density of juveniles, pointing to two reproductive periods. We hypothesized that oribatid mite trophic structure changes due to variations in abiotic (e.g., tidal dynamics, temperature) and biotic conditions (e.g., resource availability). Stable isotope (15N, 13C) and neutral lipid fatty acid analyses indicated that oribatid mite species have different diets with e.g., Z. quadrivertex feeding on macroalgae and fungi, A. schneideri feeding on microalgae and bacteria, and Scheloribates laevigatus and M. neglecta feeding on dead organic matter, bacteria and fungi. Overall, the results indicate that oribatid mite species in salt marshes are affected by changes in environmental factors such as inundation intensity, with the effects being most pronounced in species with narrow trophic niches and limited niche plasticity. The results also indicate that oribatid mite communities of the LSM respond little to short-term (one year) changes in inundation frequency.

Flooding frequency is predicted to increase during the next decades in Europe. Therefore, it is important to understand how short-term disturbance events affect soil biota providing essential ecosystem functions and uncover factors modulating their response such as plant community composition. Here we report on the response of soil microarthropod communities (Collembola and Acari) to a severe summer flood in 2013, which affected major parts of central Europe. Collembola and Acari density and Collembola and Oribatida richness were strongly affected by the flood, but they recovered within three months. Effects of plant community composition on soil microarthropods disappeared after the flood, presumably due to homogenization of the field, but the effects of plant community were in a stage of being reasserted three months after the flood. Widespread, surface living and generalistic microarthropod species recolonized the field quickly. Prostigmata and Oribatida were more resilient or recovered to flooding than Astigmata and Gamasida. Long-term impacts, however, remain unknown and deserve further investigation.

Conversion of tropical rainforests into plantations fundamentally alters ecological niches of animal species. Generalist predators such as centipedes (Chilopoda) may be able to persist in converted ecosystems due to their ability to adapt and switch to alternative prey populations. We investigated variations in community composition and trophic niches of soil and litter living centipedes in a range of ecosystems including rainforests, jungle rubber agroforests, and rubber and oil palm monocultures in two landscapes in Sumatra, Indonesia. Including information on environmental factors in the soil and litter habitat, we explored drivers shaping ecological niches of soil living invertebrate predators in one of the world's hotspots of rainforest conversion. Conversion of rainforests into agroforests and plantations was associated with a marked change in the composition of centipede communities. However, irrespective of major differences in habitat characteristics, changes in total abundances were small and the overall diversity and biomass of centipedes was similar in each of the systems investigated, suggesting that the number of ecological niches for this group of predators remains unchanged. By using stable isotope analysis (15N and 13C), we investigated trophic niche shifts of the centipede community; lower δ13C values of centipedes in oil palm plantations as compared to other ecosystems suggests that centipedes switch from decomposer prey to other prey, presumably understory associated herbivores, due to reduced availability of litter associated prey species. The results suggest that the ability to utilize alternative prey is a key feature enabling invertebrate predators to persist in ecosystems undergoing major structural changes due to anthropogenic land use change.

Soil food web structure and function is primarily determined by the major basal resources, which are living plant tissue, root exudates and dead organic matter. A field experiment was performed to disentangle the interlinkage of the root-and detritus-based soil food chains. An arable site was cropped either with maize, amended with maize shoot litter or remained bare soil, representing food webs depending on roots, aboveground litter and soil organic matter as predominant resource, respectively. The soil micro-food web, i.e. microorganisms and nematodes, was investigated in two successive years along a depth transect. The community composition of nematodes was used as model to determine the changes in the rhizosphere, detritusphere and bulk soil food web. In the first growing season the impact of treatments on the soil micro-food web was minor. In the second year plant-feeding nematodes increased under maize, whereas after harvest the Channel Index assigned promotion of the detritivore food chain, reflecting decomposition of root residues. The amendment with litter did not foster microorganisms, instead biomass of Gram-positive and Gram-negative bacteria as well as that of fungi declined in the rooted zone. Likely higher grazing pressure by nematodes reduced microbial standing crop as bacterial and fungal feeders increased. However, populations at higher trophic levels were not promoted, indicating limited flux of litter resources along the food chain. After two years of bare soil microbial biomass and nematode density remained stable, pointing to soil organic matter-based resources that allow bridging periods with deprivation. Nematode communities were dominated by opportunistic taxa that are competitive at moderate resource supply. In sum, removal of plants from the system had less severe effects than expected, suggesting considerable food web resilience to the disruption of both the root and detrital carbon channel, pointing to a legacy of organic matter resources in arable soils.

Mesofauna taxa fill key trophic positions in soil food webs, even in terrestrial-marine boundary habitats characterized by frequent natural disturbances. Salt marshes represent such boundary habitats, characterized by frequent inundations increasing from the terrestrial upper to the marine pioneer zone. Despite the high abundance of soil mesofauna in salt marshes and their important function by facilitating energy and carbon flows, the structure, trophic ecology and habitat-related diet shifts of mesofauna species in natural salt marsh habitats is virtually unknown. Therefore, we investigated the effects of natural disturbance (inundation frequency) on community structure, food web complexity and resource use of soil mesofauna using stable isotope analysis (15N, 13C) in three salt marsh zones. In this intertidal habitat, the pioneer zone is exposed to inundations twice a day, but lower and upper salt marshes are less frequently inundated based on shore height. The mesofauna comprised 86 species / taxa dominated by Collembola, Oribatida and Mesostigmata. Shifts in environmental disturbances influenced the structure of food webs, diversity and density declined strongly from the land to the sea pointing to the importance of increasing levels of inundation frequency. Accordingly, the reduced diversity and density was associated by a simplification of the food web in the pioneer zone as compared to the less inundated lower and upper salt marsh with a higher number of trophic levels. Strong variations in δ15N signatures demonstrated that mesofauna species are feeding at multiple trophic levels. Primary decomposers were low and most mesofauna species functioned as secondary decomposers or predators including second order predators or scavengers. The results document that major decomposer taxa, such as Collembola and Oribatida, are more diverse than previously assumed and predominantly dwell on autochthonous resources of the respective salt marsh zone. The results further suggest that Mesostigmata mostly adopt an intraguild predation lifestyle. The high trophic position of a large number of predators suggests that intraguild predation is of significant importance in salt marsh food webs. Presumably, intraguild predation contributes to stabilizing the salt marsh food web against disturbances.

Climatic and biome changes of the past million years influenced the population structure and genetic diversity of soil-living arthropods in Europe. However, their effects on the genetic structure of widespread and abundant soil animal species such as the Collembola Parisotoma notabilis remain virtually unknown. This generalist and parthenogenetic species is an early colonizer of disturbed habitats and often occurs in human modified environments. To investigate ancient climatic influence and recent distributions on the genetic structure of P. notabilis we analyzed populations on a pan-European scale using three genetic markers differing in substitution rates. The results showed that P. notabilis comprises several genetic lineages with distinct distribution ranges that diverged in the Miocene. Genetic distances of COI between lineages ranged between 15% and 18% and molecular clock estimates suggest Late Miocene divergences considering the standard arthropod rate of 2.3% per my. Compared to other soil-living arthropods like oribatid mites, European lineages of P. notabilis are rather young and genetically uniform. The close association with anthropogenic habitats presumably contributed to rapid spread in Europe.

Evidence is increasing that soil animal food webs are fueled by root-derived carbon (C) and also by root-derived nitrogen (N). Functioning as link between the above- and belowground system, trees and their species identity are important drivers structuring soil animal communities. A pulse labeling experiment using 15N and 13C was conducted by exposing beech (Fagus sylvatica) and ash (Fraxinus excelsior) seedlings to 13CO2 enriched atmosphere and tree leaves to 15N ammonium chloride solution in a plant growth chamber under controlled conditions for 72 h. C and N fluxes into the soil animal food web of beech, associated with ectomycorrhizal fungi (EMF), and ash, associated with arbuscular mycorrhizal fungi (AMF), were investigated at two sampling dates (5 and 20 days after labeling). All of the soil animal taxa studied incorporated root-derived C, while root-derived N was only incorporated into certain taxa. Tree species identity strongly affected C and N incorporation with the incorporation in the beech rhizosphere generally exceeding that in the ash rhizosphere. Incorporation differed little between 5 and 20 days after labeling indicating that both C and N are incorporated quickly into soil animals and are used for tissue formation. Our results suggest that energy and nutrient fluxes in soil food webs depend on the identity of tree species with the differences being associated with different types of mycorrhiza. Further research is needed to prove the generality of these findings and to quantify the flux of plant C and N into soil food webs of forests and other terrestrial ecosystems.

Large areas of tropical rainforest are being converted to agricultural and plantation land uses, but little is known of biodiversity and ecological functioning under these replacement land uses. We investigated the effects of conversion of rainforest into jungle rubber, intensive rubber and oil palm plantations on testate amoebae, diverse and functionally important protists in litter and soil. Living testate amoebae species richness, density and biomass were all lower in replacement land uses than in rainforest, with the impact being more pronounced in litter than in soil. Similar abundances of species of high and low trophic level in rainforest suggest that trophic interactions are more balanced, with a high number of functionally redundant species, than in rubber and oil palm. In contrast, plantations had a low density of high trophic level species indicating losses of functions. This was particularly so in oil palm plantations. In addition, the relative density of species with siliceous shells was >50% lower in the litter layer of oil palm and rubber compared to rainforest and jungle rubber. This difference suggests that rainforest conversion changes biogenic silicon pools and increases silicon losses. Overall, the lower species richness, density and biomass in plantations than in rainforest, and the changes in the functional composition of the testate amoebae community, indicate detrimental effects of rainforest conversion on the structure and functioning of microbial food webs.

Flooding frequency is predicted to increase during the next decades, calling for a better understanding of impacts on terrestrial ecosystems and for developing strategies to mitigate potential damage. Plant diversity is expected to buffer flooding effects by providing a broad range of species' responses. Here we report on the response of soil processes to a severe summer flood in 2013, which affected major parts of central Europe. We compared soil microbial respiration, biomass, nutrient limitation and enzyme activity in a grassland biodiversity experiment in Germany before flooding, one week and three months after the flood. Microbial biomass was reduced in the severely flooded plots at high, but not at low plant functional group richness. Flooding alleviated microbial nitrogen limitation, presumably due the input of nutrient-rich sediments. Further, the activity of soil enzymes including 1,4-β-N-acetylglucosaminidase, phenol oxidase and peroxidase increased with flooding severity, suggesting increased chitin and lignin degradation as a consequence of the input of detritus in sediments. Flooding effects were enhanced at higher plant diversity, indicating that plant diversity temporarily reduces stability of soil processes during flooding. The long-term impacts, however, remain unknown and deserve further investigation.

BackgroundLoss of biodiversity and increased nutrient inputs are two of the most crucial anthropogenic factors driving ecosystem change. Although both received considerable attention in previous studies, information on their interactive effects on ecosystem functioning is scarce. In particular, little is known on how soil biota and their functions are affected by combined changes in plant diversity and fertilization.Methodology/principal findingsWe investigated the effects of plant diversity, functional community composition, and fertilization on the biomass and respiration of soil microbial communities in a long-term biodiversity experiment in semi-natural grassland (Jena Experiment). Plant species richness enhanced microbial basal respiration and microbial biomass, but did not significantly affect microbial specific respiration. In contrast, the presence of legumes and fertilization significantly decreased microbial specific respiration, without altering microbial biomass. The effect of legumes was superimposed by fertilization as indicated by a significant interaction between the presence of legumes and fertilization. Further, changes in microbial stoichiometry (C-to-N ratio) and specific respiration suggest the presence of legumes to reduce N limitation of soil microorganisms and to modify microbial C use efficiency.Conclusions/significanceOur study highlights the role of plant species and functional group diversity as well as interactions between plant community composition and fertilizer application for soil microbial functions. Our results suggest soil microbial stoichiometry to be a powerful indicator of microbial functioning under N limited conditions. Although our results support the notion that plant diversity and fertilizer application independently affect microbial functioning, legume effects on microbial N limitation were superimposed by fertilization, indicating significant interactions between the functional composition of plant communities and nutrient inputs for soil processes.

BackgroundInfiltration is a key process in determining the water balance, but so far effects of earthworms, soil texture, plant species diversity and their interaction on infiltration capacity have not been studied.Methodology/principal findingsWe measured infiltration capacity in subplots with ambient and reduced earthworm density nested in plots of different plant species (1, 4, and 16 species) and plant functional group richness and composition (1 to 4 groups; legumes, grasses, small herbs, tall herbs). In summer, earthworm presence significantly increased infiltration, whereas in fall effects of grasses and legumes on infiltration were due to plant-mediated changes in earthworm biomass. Effects of grasses and legumes on infiltration even reversed effects of texture. We propose two pathways: (i) direct, probably by modifying the pore spectrum and (ii) indirect, by enhancing or suppressing earthworm biomass, which in turn influenced infiltration capacity due to change in burrowing activity of earthworms.Conclusions/significanceOverall, the results suggest that spatial and temporal variations in soil hydraulic properties can be explained by biotic processes, especially the presence of certain plant functional groups affecting earthworm biomass, while soil texture had no significant effect. Therefore biotic parameters should be taken into account in hydrological applications.

Parthenogenetic lineages may colonize marginal areas of the range of related sexual species or coexist with sexual species in the same habitat. Frozen-Niche-Variation and General-Purpose-Genotype are two hypotheses suggesting that competition and interclonal selection result in parthenogenetic populations being either genetically diverse or rather homogeneous. The cosmopolitan parthenogenetic oribatid mite Oppiella nova has a broad ecological phenotype and is omnipresent in a variety of habitats. Morphological variation in body size is prominent in this species and suggests adaptation to distinct environmental conditions. We investigated genetic variance and body size of five independent forest - grassland ecotones. Forests and grasslands were inhabited by distinct genetic lineages with transitional habitats being colonized by both genetic lineages from forest and grassland. Notably, individuals of grasslands were significantly larger than individuals in forests. These differences indicate the presence of specialized genetic lineages specifically adapted to either forests or grasslands which coexist in transitional habitats. Molecular clock estimates suggest that forest and grassland lineages separated 16-6 million years ago, indicating long-term persistence of these lineages in their respective habitat. Long-term persistence, and morphological and genetic divergence imply that drift and environmental factors result in the evolution of distinct parthenogenetic lineages resembling evolution in sexual species. This suggests that parthenogenetic reproduction is not an evolutionary dead end.

The availability of high quality resources is an important factor driving community structure and reproductive mode of animals. Parthenogenetic reproduction prevails when resources are available in excess, whereas sexuality correlates with resource shortage. We investigated the effect of resource availability on the community structure of oribatid mites in a laboratory experiment. Availability of food resources was increased by addition of glucose to leaf litter and reduced by leaching of nutrients from leaf litter. Experimental systems were incubated at three different temperatures to establish different regimes of resource exploitation. Community structure of oribatids and numbers of eggs per female were measured over a period of ten months. We expected the density of oribatid mites to decline in the reduced litter quality treatment but to increase in the glucose treatment. Both effects were assumed to be more pronounced at higher temperatures. We hypothesized sexual species to be less affected than parthenogenetic species by reduced resource quality due to higher genetic diversity allowing more efficient exploitation of limited resources, but to be outnumbered by parthenogenetic species in case of resource addition due to faster reproduction. In contrast to our hypotheses, both sexual and parthenogenetic oribatid mite species responded similarly with their densities declining uniformly during incubation. The parthenogenetic Brachychthoniidae and Tectocepheus dominated early in the experiment but were replaced later by parthenogenetic Desmonomata and Rhysotritia. In parthenogenetic species the number of eggs per female increased during the experiment while the number of eggs in sexual females remained constant or decreased slightly; in general, egg numbers were higher in sexual than in parthenogenetic species. The results indicate that for sustaining oribatid mite populations other resources than litter and associated saprotrophic microorganisms are needed. They also indicate that there are two groups of parthenogenetically reproducing species: exploiters of easily available resources and consumers of leaf litter associated resources.

Plant diversity drives changes in the soil microbial community which may result in alterations in ecosystem functions. However, the governing factors between the composition of soil microbial communities and plant diversity are not well understood. We investigated the impact of plant diversity (plant species richness and functional group richness) and plant functional group identity on soil microbial biomass and soil microbial community structure in experimental grassland ecosystems. Total microbial biomass and community structure were determined by phospholipid fatty acid (PLFA) analysis. The diversity gradient covered 1, 2, 4, 8, 16 and 60 plant species and 1, 2, 3 and 4 plant functional groups (grasses, legumes, small herbs and tall herbs). In May 2007, soil samples were taken from experimental plots and from nearby fields and meadows. Beside soil texture, plant species richness was the main driver of soil microbial biomass. Structural equation modeling revealed that the positive plant diversity effect was mainly mediated by higher leaf area index resulting in higher soil moisture in the top soil layer. The fungal-to-bacterial biomass ratio was positively affected by plant functional group richness and negatively by the presence of legumes. Bacteria were more closely related to abiotic differences caused by plant diversity, while fungi were more affected by plant-derived organic matter inputs. We found diverse plant communities promoted faster transition of soil microbial communities typical for arable land towards grassland communities. Although some mechanisms underlying the plant diversity effect on soil microorganisms could be identified, future studies have to determine plant traits shaping soil microbial community structure. We suspect differences in root traits among different plant communities, such as root turnover rates and chemical composition of root exudates, to structure soil microbial communities.

Some soil bacteria protect plants against soil-borne diseases by producing toxic secondary metabolites. Such beneficial biocontrol bacteria can be used in agricultural systems as alternative to agrochemicals. The broad spectrum toxins responsible for plant protection also inhibit predation by protozoa and nematodes, the main consumers of bacteria in soil. Therefore, predation pressure may favour biocontrol bacteria and contribute to plant health. We analyzed the effect of Acanthamoeba castellanii on semi-natural soil bacterial communities in a microcosm experiment. We determined the frequency of culturable bacteria carrying genes responsible for the production of the antifungal compounds 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin (PRN) and hydrogen cyanide (HCN) in presence and absence of A. castellanii. We then measured if amoebae affected soil suppressiveness in a bioassay with sugar beet seedlings confronted to the fungal pathogen Rhizoctonia solani. Amoebae increased the frequency of both DAPG and HCN positive bacteria in later plant growth phases (2 and 3 weeks), as well as the average number of biocontrol genes per bacterium. The abundance of DAPG positive bacteria correlated with disease suppression, suggesting that their promotion by amoebae may enhance soil health. However, the net effect of amoebae on soil suppressiveness was neutral to slightly negative, possibly because amoebae slow down the establishment of biocontrol bacteria on the recently emerged seedlings used in the assay. The results indicate that microfaunal predators foster biocontrol bacterial communities. Understanding interactions between biocontrol bacteria and their predators may thus help developing environmentally friendly management practices of agricultural systems.

Very few principles have been unraveled that explain the relationship between soil properties and soil biota across large spatial scales and different land-use types. Here, we seek these general relationships using data from 52 differently managed grassland and forest soils in three study regions spanning a latitudinal gradient in Germany. We hypothesize that, after extraction of variation that is explained by location and land-use type, soil properties still explain significant proportions of variation in the abundance and diversity of soil biota. If the relationships between predictors and soil organisms were analyzed individually for each predictor group, soil properties explained the highest amount of variation in soil biota abundance and diversity, followed by land-use type and sampling location. After extraction of variation that originated from location or land-use, abiotic soil properties explained significant amounts of variation in fungal, meso- and macrofauna, but not in yeast or bacterial biomass or diversity. Nitrate or nitrogen concentration and fungal biomass were positively related, but nitrate concentration was negatively related to the abundances of Collembola and mites and to the myriapod species richness across a range of forest and grassland soils. The species richness of earthworms was positively correlated with clay content of soils independent of sample location and land-use type. Our study indicates that after accounting for heterogeneity resulting from large scale differences among sampling locations and land-use types, soil properties still explain significant proportions of variation in fungal and soil fauna abundance or diversity. However, soil biota was also related to processes that act at larger spatial scales and bacteria or soil yeasts only showed weak relationships to soil properties. We therefore argue that more general relationships between soil properties and soil biota can only be derived from future studies that consider larger spatial scales and different land-use types.

BACKGROUND: Stability is a crucial ecosystem feature gaining particular importance in face of increasing anthropogenic stressors. Biodiversity is considered to be a driving biotic force maintaining stability, and in this study we investigate how different indices of biodiversity affect the stability of communities in varied abiotic (composition of available resources) and biotic (invasion) contexts. METHODOLOGY/PRINCIPAL FINDINGS: We set up microbial microcosms to study the effects of genotypic diversity on the reliability of community productivity, defined as the inverse of the coefficient of variation of across-treatment productivity, in different environmental contexts. We established a bacterial diversity gradient ranging from 1 to 8 Pseudomonas fluorescens genotypes and grew the communities in different resource environments or in the presence of model invasive species. Biodiversity significantly stabilized community productivity across treatments in both experiments. Path analyses revealed that different aspects of diversity determined stability: genotypic richness stabilized community productivity across resource environments, whereas functional diversity determined stability when subjected to invasion. CONCLUSIONS/SIGNIFICANCE: Biodiversity increases the stability of microbial communities against both biotic and abiotic environmental perturbations. Depending on stressor type, varying aspects of biodiversity contribute to the stability of ecosystem functions. The results suggest that both genetic and functional diversity need to be preserved to ensure buffering of communities against abiotic and biotic stresses.

Tropical regions are facing increasing atmospheric inputs of nutrients, which will have unknown consequences for the structure and functioning of these systems. Here, we show that Neotropical montane rainforests respond rapidly to moderate additions of N (50 kg ha(-1) yr(-1)) and P (10 kg ha(-1) yr(-1)). Monitoring of nutrient fluxes demonstrated that the majority of added nutrients remained in the system, in either soil or vegetation. N and P additions led to not only an increase in foliar N and P concentrations, but also altered soil microbial biomass, standing fine root biomass, stem growth, and litterfall. The different effects suggest that trees are primarily limited by P, whereas some processes-notably aboveground productivity--are limited by both N and P. Highly variable and partly contrasting responses of different tree species suggest marked changes in species composition and diversity of these forests by nutrient inputs in the long term. The unexpectedly fast response of the ecosystem to moderate nutrient additions suggests high vulnerability of tropical montane forests to the expected increase in nutrient inputs.

One of the most significant consequences of contemporary global change is the rapid decline of biodiversity in many ecosystems. Knowledge of the consequences of biodiversity loss in terrestrial ecosystems is largely restricted to single ecosystem functions. Impacts of key plant functional groups on soil biota are considered to be more important than those of plant diversity; however, current knowledge mainly relies on short-term experiments.We studied changes in the impacts of plant diversity and presence of key functional groups on soil biota by investigating the performance of soil microorganisms and soil fauna two, four and six years after the establishment of model grasslands. The results indicate that temporal changes of plant community effects depend on the trophic affiliation of soil animals: plant diversity effects on decomposers only occurred after six years, changed little in herbivores, but occurred in predators after two years. The results suggest that plant diversity, in terms of species and functional group richness, is the most important plant community property affecting soil biota, exceeding the relevance of plant above- and belowground productivity and the presence of key plant functional groups, i.e. grasses and legumes, with the relevance of the latter decreasing in time.Plant diversity effects on biota are not only due to the presence of key plant functional groups or plant productivity highlighting the importance of diverse and high-quality plant derived resources, and supporting the validity of the singular hypothesis for soil biota. Our results demonstrate that in the long term plant diversity essentially drives the performance of soil biota questioning the paradigm that belowground communities are not affected by plant diversity and reinforcing the importance of biodiversity for ecosystem functioning.

Changes in plant diversity may induce distinct changes in soil food web structure and accompanying soil feedbacks to plants. However, knowledge of the long-term consequences of plant community simplification for soil animal food webs and functioning is scarce. Nematodes, the most abundant and diverse soil Metazoa, represent the complexity of soil food webs as they comprise all major trophic groups and allow calculation of a number of functional indices.We studied the functional composition of nematode communities three and five years after establishment of a grassland plant diversity experiment (Jena Experiment). In response to plant community simplification common nematode species disappeared and pronounced functional shifts in community structure occurred. The relevance of the fungal energy channel was higher in spring 2007 than in autumn 2005, particularly in species-rich plant assemblages. This resulted in a significant positive relationship between plant species richness and the ratio of fungal-to-bacterial feeders. Moreover, the density of predators increased significantly with plant diversity after five years, pointing to increased soil food web complexity in species-rich plant assemblages. Remarkably, in complex plant communities the nematode community shifted in favour of microbivores and predators, thereby reducing the relative abundance of plant feeders after five years.The results suggest that species-poor plant assemblages may suffer from nematode communities detrimental to plants, whereas species-rich plant assemblages support a higher proportion of microbivorous nematodes stimulating nutrient cycling and hence plant performance; i.e. effects of nematodes on plants may switch from negative to positive. Overall, food web complexity is likely to decrease in response to plant community simplification and results of this study suggest that this results mainly from the loss of common species which likely alter plant-nematode interactions.

The diversity-stability hypothesis states that current losses of biodiversity can impair the ability of an ecosystem to dampen the effect of environmental perturbations on its functioning. Using data from a long-term and comprehensive biodiversity experiment, we quantified the temporal stability of 42 variables characterizing twelve ecological functions in managed grassland plots varying in plant species richness. We demonstrate that diversity increases stability i) across trophic levels (producer, consumer), ii) at both the system (community, ecosystem) and the component levels (population, functional group, phylogenetic clade), and iii) primarily for aboveground rather than belowground processes. Temporal synchronization across studied variables was mostly unaffected with increasing species richness. This study provides the strongest empirical support so far that diversity promotes stability across different ecological functions and levels of ecosystem organization in grasslands.

BackgroundInvasions of natural communities by non-indigenous species are currently rated as one of the most important global-scale threats to biodiversity. Biodiversity itself is known to reduce invasions and increase stability. Disturbances by ecosystem engineers affect the distribution, establishment, and abundance of species but this has been ignored in studies on diversity-invasibility relationships.Methodology/principal findingsWe determined natural plant invasion into 46 plots varying in the number of plant species (1, 4, and 16) and plant functional groups (1, 2, 3, and 4) for three years beginning two years after the establishment of the Jena Experiment. We sampled subplots where earthworms were artificially added and others where earthworm abundance was reduced. We also performed a seed-dummy experiment to investigate the role of earthworms as secondary seed dispersers along a plant diversity gradient. Horizontal dispersal and burial of seed dummies were significantly reduced in subplots where earthworms were reduced in abundance. Seed dispersal by earthworms decreased with increasing plant species richness and presence of grasses but increased in presence of small herbs. These results suggest that dense vegetation inhibits the surface activity of earthworms. Further, there was a positive relationship between the number of earthworms and the number and diversity of invasive plants. Hence, earthworms decreased the stability of grassland communities against plant invasion.Conclusions/significanceInvasibility decreased and stability increased with increasing plant diversity and, most remarkably, earthworms modulated the diversity-invasibility relationship. While the impacts of earthworms were unimportant in low diverse (low earthworm densities) and high diverse (high floral structural complexity) plant communities, earthworms decreased the stability of intermediate diverse plant communities against plant invasion. Overall, the results document that fundamental processes in plant communities like plant seed burial and invader establishment are modulated by soil fauna calling for closer cooperation between soil animal and plant ecologists.