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Fauna is highly abundant and diverse in soils worldwide, but surprisingly little is known about how it affects soil organic matter stabilization. Here, we review how the ecological strategies of a multitude of soil faunal taxa can affect the formation and persistence of labile (particulate organic matter, POM) and stabilized soil organic matter (mineral-associated organic matter, MAOM). We propose three major mechanisms - transformation, translocation, and grazing on microorganisms - by which soil fauna alters factors deemed essential in the formation of POM and MAOM, including the quantity and decomposability of organic matter, soil mineralogy, and the abundance, location, and composition of the microbial community. Determining the relevance of these mechanisms to POM and MAOM formation in cross-disciplinary studies that cover individual taxa and more complex faunal communities, and employ physical fractionation, isotopic, and microbiological approaches is essential to advance concepts, models, and policies focused on soil organic matter and effectively manage soils as carbon sinks, nutrient stores, and providers of food. In their review, Angst et al. conceptualize how the ecological strategies of a multitude of soil faunal taxa can influence the formation of particulate and mineral-associated organic matter. The authors highlight research gaps and ways forward. [ABSTRACT FROM AUTHOR]

The currently dominant types of land management are threatening the multifunctionality of ecosystems, which is vital for human well-being. Here, we present a novel ecological-economic assessment of how multifunctionality of agroecosystems in Central Germany depends on land-use type and climate. Our analysis includes 14 ecosystem variables in a large-scale field experiment with five different land-use types under two different climate scenarios (ambient and future climate). We consider ecological multifunctionality measures using averaging approaches with different weights, reflecting preferences of four relevant stakeholders based on adapted survey data. Additionally, we propose an economic multifunctionality measure based on the aggregate economic value of ecosystem services. Results show that intensive management and future climate decrease ecological multifunctionality for most scenarios in both grassland and cropland. Only under a weighting based on farmers' preferences, intensively-managed grassland shows higher multifunctionality than sustainably-managed grassland. The economic multifunctionality measure is about ~1.7 to 1.9 times higher for sustainable, compared to intensive, management for both grassland and cropland. Soil biodiversity correlates positively with ecological multifunctionality and is expected to be one of its drivers. As the currently prevailing land management provides high multifunctionality for farmers, but not for society at large, we suggest to promote and economically incentivise sustainable land management that enhances both ecological and economic multifunctionality, also under future climatic conditions. Land management impacts ecosystem functions. Here, the authors conduct field experiments in Germany assessing ecosystem variables in cropland and grasslands showing that sustainable agricultural practices enhance ecological and economic benefits. [ABSTRACT FROM AUTHOR]

The relationship between biodiversity and ecosystem functioning strengthens with ecosystem age. However, the interplay between the plant diversity - ecosystem functioning relationship and Glomeromycotinian arbuscular mycorrhizal fungi (AMF) community assembly has not yet been scrutinized in this context, despite AMF's role in plant survival and niche exploration. We study the development of AMF communities by disentangling soil- and plant-driven effects from calendar year effects. Within a long-term grassland biodiversity experiment, the pre-existing plant communities of varying plant diversity were re-established as split plots with combinations of common plant and soil histories: split plots with neither common plant nor soil history, with only soil but no plant history, and with both common plant and soil history. We found that bulk soil AMF communities were primarily shaped by common soil history, and additional common plant history had little effect. Further, the steepness of AMF diversity and plant diversity relationship did not strengthen over time, but AMF community evenness increased with common history. Specialisation of AMF towards plant species was low throughout, giving no indication of AMF communities specialising or diversifying over time. The potential of bulk soil AMF as mediators of variation in plant and microbial biomass over time and hence as drivers of biodiversity and ecosystem relationships was low. Our results suggest that soil processes may be key for the build-up of plant community-specific mycorrhizal communities with likely feedback effects on ecosystem productivity, but the plant-available mycorrhizal pool in bulk soil itself does not explain the strengthening of biodiversity and ecosystem relationships over time. [ABSTRACT FROM AUTHOR]

Plant diversity effects on community productivity often increase over time. Whether the strengthening of diversity effects is caused by temporal shifts in species-level overyielding (i.e., higher species-level productivity in diverse communities compared with monocultures) remains unclear. Here, using data from 65 grassland and forest biodiversity experiments, we show that the temporal strength of diversity effects at the community scale is underpinned by temporal changes in the species that yield. These temporal trends of species-level overyielding are shaped by plant ecological strategies, which can be quantitatively delimited by functional traits. In grasslands, the temporal strengthening of biodiversity effects on community productivity was associated with increasing biomass overyielding of resource-conservative species increasing over time, and with overyielding of species characterized by fast resource acquisition either decreasing or increasing. In forests, temporal trends in species overyielding differ when considering above- versus belowground resource acquisition strategies. Overyielding in stem growth decreased for species with high light capture capacity but increased for those with high soil resource acquisition capacity. Our results imply that a diversity of species with different, and potentially complementary, ecological strategies is beneficial for maintaining community productivity over time in both grassland and forest ecosystems.Species-rich plant communities often have higher productivity than monocultures. Here, the authors analyse biodiversity-ecosystem functioning experiments in grasslands and forests and find that the biodiversity effects on community productivity strengthen over time thanks to shifts in contributions of species with different resource acquisition traits. [ABSTRACT FROM AUTHOR]

Plant nutrient uptake and productivity are driven by a multitude of factors that have been modified by human activities, like climate change and the activity of decomposers. However, interactive effects of climate change and key decomposer groups like earthworms have rarely been studied. In a field microcosm experiment, we investigated the effects of a mean future climate scenario with warming (+ 0.50 °C to + 0.62 °C) and altered precipitation (+ 10% in spring and autumn, − 20% in summer) and earthworms (anecic—two Lumbricus terrestris, endogeic—four Allolobophora chlorotica and both together within 10 cm diameter tubes) on plant biomass and stoichiometry in two land-use types (intensively used meadow and conventional farming). We found little evidence for earthworm effects on aboveground biomass. However, future climate increased above- (+40.9%) and belowground biomass (+44.7%) of grass communities, which was mainly driven by production of the dominant Festulolium species during non-summer drought periods, but decreased the aboveground biomass (− 36.9%) of winter wheat. Projected climate change and earthworms interactively affected the N content and C:N ratio of grasses. Earthworms enhanced the N content (+1.2%) thereby decreasing the C:N ratio (− 4.1%) in grasses, but only under ambient climate conditions. The future climate treatment generally decreased the N content of grasses (aboveground: − 1.1%, belowground: − 0.15%) and winter wheat (− 0.14%), resulting in an increase in C:N ratio of grasses (aboveground: + 4.2%, belowground: +6.3%) and wheat (+5.9%). Our results suggest that climate change diminishes the positive effects of earthworms on plant nutrient uptakes due to soil water deficit, especially during summer drought. [ABSTRACT FROM AUTHOR]

Eutrophication usually impacts grassland biodiversity, community composition, and biomass production, but its impact on the stability of these community aspects is unclear. One challenge is that stability has many facets that can be tightly correlated (low dimensionality) or highly disparate (high dimensionality). Using standardized experiments in 55 grassland sites from a globally distributed experiment (NutNet), we quantify the effects of nutrient addition on five facets of stability (temporal invariability, resistance during dry and wet growing seasons, recovery after dry and wet growing seasons), measured on three community aspects (aboveground biomass, community composition, and species richness). Nutrient addition reduces the temporal invariability and resistance of species richness and community composition during dry and wet growing seasons, but does not affect those of biomass. Different stability measures are largely uncorrelated under both ambient and eutrophic conditions, indicating consistently high dimensionality. Harnessing the dimensionality of ecological stability provides insights for predicting grassland responses to global environmental change. Anthropogenic eutrophication is a driver of plant community shifts in many grassland ecosystems. Here, the authors use data from a globally distributed experiment to assess how nutrient addition affects multiple facets of grassland ecological stability and their correlations. [ABSTRACT FROM AUTHOR]

This document is a reply to a comment made by C. Yue et al. regarding a study on soil microbial carbon. The authors of the reply address the concerns raised by Yue et al. and provide additional analysis. They argue that the relationship between temperature and soil microbial carbon is context-dependent and non-linear. They also discuss the limitations of the datasets used by Yue et al. and emphasize the need for more comprehensive studies on soil microbial carbon. The authors acknowledge the importance of global soil monitoring initiatives and the development of mechanistic models. [Extracted from the article]

A variety of human activities have been identified as driving factors for the release and spread of invasive earthworm species in North America. Population genetic markers can help to identify locally relevant anthropogenic vectors and provide insights into the processes of population dispersal and establishment. We sampled the invasive European earthworm species Lumbricus terrestris at nine sites and several bait shops within the metropolitan area of Minneapolis-St. Paul in Minnesota, USA. We used microsatellite markers to infer genetic diversity and population structure, and 16S rDNA to address multiple introduction events, including bait dumping, which is a common source of L. terrestris introductions into the wild. Our results indicate multiple introductions but not from current bait dumping. Overall, genetic structure was low and earthworms > 5,000 m apart were genetically differentiated, except for one sampling location, indicating jump-dispersal followed by population establishment. Further, earthworms at one location north of Minneapolis established from one or few founder individuals, suggesting that earthworm invasions are ongoing. We therefore encourage further monitoring of earthworm populations using molecular markers, in order to disentangle the different human-related vectors contributing to the spread of earthworms and their establishment, which is essential to develop adequate management strategies. [ABSTRACT FROM AUTHOR]

Long-term observations have shown that many plants and aboveground animals have changed their phenology patterns due to warmer temperatures over the past decades. However, empirical evidence for phenological shifts in alpine organisms, particularly belowground organisms, is scarce. Here, we investigate how the activities and phenology of plants, soil microbes, and soil fauna will respond to warming in an alpine meadow on the Tibetan Plateau, and whether their potential phenological changes will be synchronized. We experimentally simulate an increase in soil temperature by 2–4 °C according to future projections for this region. We find that warming promotes plant growth, soil microbial respiration, and soil fauna feeding by 8%, 57%, and 20%, respectively, but causes dissimilar changes in their phenology during the growing season. Specifically, warming advances soil faunal feeding activity in spring and delays it in autumn, while their peak activity does not change; whereas warming increases the peak activity of plant growth and soil microbial respiration but with only minor shifts in their phenology. Such phenological asynchrony in alpine organisms may alter ecosystem functioning and stability. Phenological shifts driven by climate change are well-studied in plants and aboveground animals, but scarcely in belowground biota. Here, the authors show that soil warming causes phenological mismatches between plants, soil microbes and soil microarthropods in an alpine meadow. [ABSTRACT FROM AUTHOR]

Plant productivity varies due to environmental heterogeneity, and theory suggests that plant diversity can reduce this variation. While there is strong evidence of diversity effects on temporal variability of productivity, whether this mechanism extends to variability across space remains elusive. Here we determine the relationship between plant diversity and spatial variability of productivity in 83 grasslands, and quantify the effect of experimentally increased spatial heterogeneity in environmental conditions on this relationship. We found that communities with higher plant species richness (alpha and gamma diversity) have lower spatial variability of productivity as reduced abundance of some species can be compensated for by increased abundance of other species. In contrast, high species dissimilarity among local communities (beta diversity) is positively associated with spatial variability of productivity, suggesting that changes in species composition can scale up to affect productivity. Experimentally increased spatial environmental heterogeneity weakens the effect of plant alpha and gamma diversity, and reveals that beta diversity can simultaneously decrease and increase spatial variability of productivity. Our findings unveil the generality of the diversity-stability theory across space, and suggest that reduced local diversity and biotic homogenization can affect the spatial reliability of key ecosystem functions. The insurance hypothesis posits that more diverse communities are more stable through time. Here, the authors show that plant biodiversity reduces the spatial variability of productivity in grassland communities, demonstrating that the insurance hypothesis applies also across space. [ABSTRACT FROM AUTHOR]

Numerous studies have demonstrated that biodiversity drives ecosystem functioning, yet how biodiversity loss alters ecosystems functioning and stability in the long-term lacks experimental evidence. We report temporal effects of species richness on community productivity, stability, species asynchrony, and complementarity, and how the relationships among them change over 17 years in a grassland biodiversity experiment. Productivity declined more rapidly in less diverse communities resulting in temporally strengthening positive effects of richness on productivity, complementarity, and stability. In later years asynchrony played a more important role in increasing community stability as the negative effect of richness on population stability diminished. Only during later years did species complementarity relate to species asynchrony. These results show that species complementarity and asynchrony can take more than a decade to develop strong stabilizing effects on ecosystem functioning in diverse plant communities. Thus, the mechanisms stabilizing ecosystem functioning change with community age. Biodiversity-ecosystem functioning relationships may change over time. Here, Wagg et al. show that richness-productivity and richness stability relationships grow stronger over time in an experimental grassland community, and shed light on the ecological mechanisms. [ABSTRACT FROM AUTHOR]

Soils are the foundation of all terrestrial ecosystems1. However, unlike for plants and animals, a global assessment of hotspots for soil nature conservation is still lacking2. This hampers our ability to establish nature conservation priorities for the multiple dimensions that support the soil system: from soil biodiversity to ecosystem services. Here, to identify global hotspots for soil nature conservation, we performed a global field survey that includes observations of biodiversity (archaea, bacteria, fungi, protists and invertebrates) and functions (critical for six ecosystem services) in 615 composite samples of topsoil from a standardized survey in all continents. We found that each of the different ecological dimensions of soils—that is, species richness (alpha diversity, measured as amplicon sequence variants), community dissimilarity and ecosystem services—peaked in contrasting regions of the planet, and were associated with different environmental factors. Temperate ecosystems showed the highest species richness, whereas community dissimilarity peaked in the tropics, and colder high-latitudinal ecosystems were identified as hotspots of ecosystem services. These findings highlight the complexities that are involved in simultaneously protecting multiple ecological dimensions of soil. We further show that most of these hotspots are not adequately covered by protected areas (more than 70%), and are vulnerable in the context of several scenarios of global change. Our global estimation of priorities for soil nature conservation highlights the importance of accounting for the multidimensionality of soil biodiversity and ecosystem services to conserve soils for future generations.A global field survey that analyses samples of soil from all continents identifies hotspots for soil nature conservation, and shows that different ecological dimensions of soil are associated with different priority areas for conservation. [ABSTRACT FROM AUTHOR]

Background and aims: The amount of nitrogen (N) derived from symbiotic N2 fixation by legumes in grasslands might be affected by anthropogenic N and phosphorus (P) inputs, but the underlying mechanisms are not known. Methods: We evaluated symbiotic N2 fixation in 17 natural and semi-natural grasslands on four continents that are subjected to the same full-factorial N and P addition experiment, using the 15N natural abundance method. Results: N as well as combined N and P (NP) addition reduced aboveground legume biomass by 65% and 45%, respectively, compared to the control, whereas P addition had no significant impact. Addition of N and/or P had no significant effect on the symbiotic N2 fixation per unit legume biomass. In consequence, the amount of N fixed annually per grassland area was less than half in the N addition treatments compared to control and P addition, irrespective of whether the dominant legumes were annuals or perennials. Conclusion: Our results reveal that N addition mainly impacts symbiotic N2 fixation via reduced biomass of legumes rather than changes in N2 fixation per unit legume biomass. The results show that soil N enrichment by anthropogenic activities significantly reduces N2 fixation in grasslands, and these effects cannot be reversed by additional P amendment. [ABSTRACT FROM AUTHOR]

Soil microorganisms are central to sustain soil functions and services, like carbon and nutrient cycling. Currently, we only have a limited understanding of the spatial-temporal dynamics of soil microorganisms, restricting our ability to assess long-term effects of climate and land-cover change on microbial roles in soil biogeochemistry. This study assesses the temporal trends in soil microbial biomass carbon and identifies the main drivers of biomass change regionally and globally to detect the areas sensitive to these environmental factors. Here, we combined a global soil microbial biomass carbon data set, random forest modelling, and environmental layers to predict spatial-temporal dynamics of microbial biomass carbon stocks from 1992 to 2013. Soil microbial biomass carbon stocks decreased globally by 3.4 ± 3.0% (mean ± 95% CI) between 1992 and 2013 for the predictable regions, equivalent to 149 Mt being lost over the period, or ~1‰ of soil C. Northern areas with high soil microbial carbon stocks experienced the strongest decrease, mostly driven by increasing temperatures. In contrast, land-cover change was a weaker global driver of change in microbial carbon, but had, in some cases, important regional effects. Soil microbial carbon is central to soil functions and services, but its spatial-temporal dynamics are unclear. Here the authors show global trends in soil microbial carbon, which suggests a global decrease in soil microbial carbon, mostly driven by temperature increases in northern areas. [ABSTRACT FROM AUTHOR]

Growing threats from extreme climatic events and biodiversity loss have raised concerns about their interactive consequences for ecosystem functioning. Evidence suggests biodiversity can buffer ecosystem functioning during such climatic events. However, whether exposure to extreme climatic events will strengthen the biodiversity-dependent buffering effects for future generations remains elusive. We assess such transgenerational effects by exposing experimental grassland communities to eight recurrent summer droughts versus ambient conditions in the field. Seed offspring of 12 species are then subjected to a subsequent drought event in the glasshouse, grown individually, in monocultures or in 2-species mixtures. Comparing productivity between mixtures and monocultures, drought-selected plants show greater between-species complementarity than ambient-selected plants when recovering from the subsequent drought, causing stronger biodiversity effects on productivity and better recovery of drought-selected mixtures after the drought. These findings suggest exposure to recurrent climatic events can improve ecosystem responses to future events through transgenerational reinforcement of species complementarity. Using experimental communities of grassland species, this study shows that drought-exposure history can accelerate recovery from subsequent drought through increased niche complementarity between species. This transgenerational effect may enhance the sustainability of biodiversity and ecosystem functioning in a future with more frequent droughts. [ABSTRACT FROM AUTHOR]

Earthworms are considered ecosystem engineers due to their fundamental impact on soil structure, soil processes and on other soil biota. An invasion of non-native earthworm species has altered soils of North America since European settlement, a process currently expanding into still earthworm-free forest ecosystems due to continuous spread and increasing soil temperatures owing to climate change. Although earthworms are known to modify soil microbial diversity and activity, it is as yet unclear how eukaryote consumers in soil microbial food webs will be affected. Here, we investigated how earthworm invasion affects the diversity of Cercozoa, one of the most dominant protist taxa in soils. Although the composition of the native cercozoan community clearly shifted in response to earthworm invasion, the communities of the different forests showed distinct responses. We identified 39 operational taxonomic units (OTUs) exclusively indicating earthworm invasion, hinting at an earthworm-associated community of Cercozoa. In particular, Woronina pythii, a hyper-parasite of plant-parasitic Oomycota in American forests, increased strongly in the presence of invasive earthworms, indicating an influence of invasive earthworms on oomycete communities and potentially on forest health, which requires further research. [ABSTRACT FROM AUTHOR]

Enough of silos: develop a joint scientific agenda to understand the intertwined global crises of the Earth system. [ABSTRACT FROM AUTHOR]

Diversity loss has been shown to change the soil community; however, little is known about long-term consequences and underlying mechanisms. Here, we investigated how nematode communities are affected by plant species richness and whether this is driven by resource quantity or quality in 15-year-old plant communities of a long-term grassland biodiversity experiment. We extracted nematodes from 93 experimental plots differing in plant species richness, and measured above- and belowground plant biomass production and soil organic carbon concentrations (Corg) as proxies for resource quantity, as well as C/Nleaf ratio and specific root length (SRL) as proxies for resource quality. We found that nematode community composition and diversity significantly differed among plant species richness levels. This was mostly due to positive plant diversity effects on the abundance and genus richness of bacterial-feeding, omnivorous, and predatory nematodes, which benefited from higher shoot mass and soil Corg in species-rich plant communities, suggesting control via resource quantity. In contrast, plant-feeding nematodes were negatively influenced by shoot mass, probably due to higher top–down control by predators, and were positively related to SRL and C/Nleaf, indicating control via resource quality. The decrease of the grazing pressure ratio (plant feeders per root mass) with plant species richness indicated a higher accumulation of plant-feeding nematodes in species-poor plant communities. Our results, therefore, support the hypothesis that soil-borne pathogens accumulate in low-diversity communities over time, while soil mutualists (bacterial-feeding, omnivorous, predatory nematodes) increase in abundance and richness in high-diversity plant communities, which may contribute to the widely-observed positive plant diversity–productivity relationship. [ABSTRACT FROM AUTHOR]

Deforestation, plantation expansion and other human activities in tropical ecosystems are often associated with biological invasions. These processes have been studied for above-ground organisms, but associated changes below the ground have received little attention. We surveyed rainforest and plantation systems in Jambi province, Sumatra, Indonesia, to investigate effects of land-use change on the diversity and abundance of earthworms—a major group of soil-ecosystem engineers that often is associated with human activities. Density and biomass of earthworms increased 4—30-fold in oil palm and rubber monoculture plantations compared to rainforest. Despite much higher abundance, earthworm communities in plantations were less diverse and dominated by the peregrine morphospecies Pontoscolex corethrurus, often recorded as invasive. Considering the high deforestation rate in Indonesia, invasive earthworms are expected to dominate soil communities across the region in the near future, in lieu of native soil biodiversity. Ecologically-friendly management approaches, increasing structural habitat complexity and plant diversity, may foster beneficial effects of invasive earthworms on plant growth while mitigating negative effects on below-ground biodiversity and the functioning of the native soil animal community. [ABSTRACT FROM AUTHOR]

Experiments showed that biodiversity increases grassland productivity and nutrient exploitation, potentially reducing fertiliser needs. Enhancing biodiversity could improve P-use efficiency of grasslands, which is beneficial given that rock-derived P fertilisers are expected to become scarce in the future. Here, we show in a biodiversity experiment that more diverse plant communities were able to exploit P resources more completely than less diverse ones. In the agricultural grasslands that we studied, management effects either overruled or modified the driving role of plant diversity observed in the biodiversity experiment. Nevertheless, we show that greater above- (plants) and belowground (mycorrhizal fungi) biodiversity contributed to tightening the P cycle in agricultural grasslands, as reduced management intensity and the associated increased biodiversity fostered the exploitation of P resources. Our results demonstrate that promoting a high above- and belowground biodiversity has ecological (biodiversity protection) and economical (fertiliser savings) benefits. Such win-win situations for farmers and biodiversity are crucial to convince farmers of the benefits of biodiversity and thus counteract global biodiversity loss. Relationships between biodiversity and phosphorus cycling and the underlying processes are complex. Here the authors analyse a biodiversity manipulation experiment and an agricultural management gradient to show how plant and mycorrhizal fungal diversity promote phosphorus exploitation. [ABSTRACT FROM AUTHOR]

Aims: Aboveground plant litter inputs are important sources of soil carbon (C). We aimed to establish how experimentally altered litter inputs affect soil C to 1-m depth across different ecosystems, and over different timeframes. Methods: We performed a meta-analysis of 237 studies across 248 sites worldwide to assess the influence of treatment magnitude, treatment duration, initial soil C content, and climate on the response of soil C to altered aboveground litter inputs. Results: Overall, soil C content was lower under litter removal, but higher under litter addition compared to controls. The effects of litter manipulation were apparent throughout the soil profile and were related to treatment magnitude. Soil C content declined markedly with increasing duration of litter removal, whereas the positive effect of litter addition attenuated over time. Cropland management practices (bare fallow or additional straw incorporation) had similar effects on soil C to litter removal and addition treatments. Conclusions: Our study reveals rapid and consistent changes in soil C content with altered litter inputs and provides important insights into plant residue management to enhance soil C sequestration. We highlight the need for long-term experiments, with a greater focus on the processes underpinning soil C storage in different ecosystems. [ABSTRACT FROM AUTHOR]

We conducted a 15N tracer experiment in laboratory microcosms with field-fresh soil samples from a biodiversity experiment to evaluate the relationship between grassland biodiversity and N cycling. To embrace the complexity of the N cycle, we determined N exchange between five soil N pools (labile and recalcitrant organic N, dissolved NH4+ and NO3− in soil solution, and exchangeable NH4+) and eight N transformations (gross N mineralization from labile and recalcitrant organic N, NH4+ immobilization into labile and recalcitrant organic N, autotrophic nitrification, heterotrophic nitrification, NO3− immobilization, adsorption of NH4+) expected in aerobic soils with the help of the N-cycle model Ntrace. We used grassland soil of the Jena Experiment, which includes plant mixtures with 1 to 60 species and 1 to 4 functional groups (legumes, grasses, tall herbs, small herbs). The 19 soil samples of one block of the Jena Experiment were labeled with either 15NH4+ or 15NO3- or both. In the presence of legumes, gross N mineralization and autotrophic nitrification increased significantly because of higher soil N concentrations in legume-containing plots and high microbial activity. Similarly, the presence of grasses significantly increased the soil NH4+ pool, gross N mineralization, and NH4+ immobilization, likely because of enhanced microbial biomass and activity by providing large amounts of rhizodeposits through their dense root systems. In our experiment, previously reported plant species richness effects on the N cycle, observed in a larger-scale field experiment within the Jena Experiment, were not seen. However, specific plant functional groups had a significant positive impact on the N cycling in the incubated soil samples. [ABSTRACT FROM AUTHOR]

Gross rates of nitrogen (N) turnover inform about the total N release and consumption. We investigated how plant diversity affects gross N mineralization, microbial ammonium (NH4+) consumption and gross inorganic N immobilization in grasslands via isotopic pool dilution. The field experiment included 74 plots with 1–16 plant species and 1–4 plant functional groups (legumes, grasses, tall herbs, small herbs). We determined soil pH, shoot height, root, shoot and microbial biomass, and C and N concentrations in soil, microbial biomass, roots and shoots. Structural equation modeling (SEM) showed that increasing plant species richness significantly decreased gross N mineralization and microbial NH4+ consumption rates via increased root C:N ratios. Root C:N ratios increased because of the replacement of legumes (low C:N ratios) by small herbs (high C:N ratios) and an increasing shoot height, which was positively related with root C:N ratios, with increasing species richness. However, in our SEM remained an unexplained direct negative path from species richness to both N turnover rates. The presence of legumes increased gross N mineralization, microbial NH4+ consumption and gross inorganic N immobilization rates likely because of improved N supply by N2 fixation. The positive effect of small herbs on microbial NH4+ consumption and gross inorganic N immobilization could be attributed to their increased rhizodeposition, stimulating microbial growth. Our results demonstrate that increasing root C:N ratios with increasing species richness slow down the N cycle but also that there must be additional, still unidentified processes behind the species richness effect potentially including changed microbial community composition. [ABSTRACT FROM AUTHOR]

Context: Soil erosion is one of the main threats driving soil degradation across the globe with important impacts on crop yields, soil biota, biogeochemical cycles, and ultimately human nutrition. Objectives: Here, using an empirical model, we present a global and temporally explicit assessment of soil erosion risk according to recent (2001–2013) dynamics of rainfall and vegetation cover change to identify vulnerable areas for soils and soil biodiversity. Methods: We used an adaptation of the Universal Soil Loss Equation together with state of the art remote sensing models to create a spatially and temporally explicit global model of soil erosion and soil protection. Finally, we overlaid global maps of soil biodiversity to assess the potential vulnerability of these soil communities to soil erosion. Results: We show a consistent decline in soil erosion protection over time across terrestrial biomes, which resulted in a global increase of 11.7% in soil erosion rates. Notably, soil erosion risk systematically increased between 2006 and 2013 in relation to the baseline year (2001). Although vegetation cover is central to soil protection, this increase was mostly driven by changes in rainfall erosivity. Globally, soil erosion is expected not only to have an impact on the vulnerability of soil conditions but also on soil biodiversity with 6.4% (for soil macrofauna) and 7.6% (for soil fungi) of these vulnerable areas coinciding with regions with high soil biodiversity. Conclusions: Our results indicate that an increasing proportion of soils are degraded globally, affecting not only livelihoods but also potentially degrading local and regional landscapes. Similarly, many degraded regions coincide with and may have impacted high levels of soil biodiversity. [ABSTRACT FROM AUTHOR]

Land-use intensification represents one major threat to the diversity and functioning of terrestrial ecosystems. In the face of concurrent climate change, concerns are growing about the ability of intensively managed agroecosystems to ensure stable food provisioning, as they may be particularly vulnerable to climate extreme-induced harvest losses and pest outbreaks. Extensively managed systems, in contrast, were shown to mitigate climate change based on plant diversity-mediated effects, such as higher functional redundancy or asynchrony of species. In this context, the maintenance of soils is essential to sustain key ecosystem functions such as nutrient cycling, pest control, and crop yield. Within the highly diverse soil fauna, nematodes represent an important group as their trophic spectrum ranges from detritivores to predators and they allow inferences to the overall state of the ecosystem (bioindicators). Here, we investigated the effects of simulated climate change and land-use intensity on the diversity and abundance of soil nematode functional groups and functional indices in two consecutive years. We revealed that especially land use induced complex shifts in the nematode community with strong seasonal dynamics, while future climate led to weaker effects. Strikingly, the high nematode densities associated with altered climatic conditions and intensive land use were a consequence of increased densities of opportunists and potential pest species (i.e., plant feeders). This coincided with a less diverse and less structured community with presumably reduced capabilities to withstand environmental stress. These degraded soil food web conditions represent a potential threat to ecosystem functioning and underline the importance of management practices that preserve belowground organisms. [ABSTRACT FROM AUTHOR]

Bottom-up effects of plants on soil communities can be modified by the activity of exotic earthworms, by altering resource availability for soil food webs through feeding, burrowing, and casting activities. The present study explored effects of plants (planting of shrubs) on soil micro-food webs (composition of soil microbial and nematode communities), and whether these effects were altered by the activity of exotic earthworms (exotic earthworms addition). Planted shrubs resulted in a non-significant increase of bacterial biomass and significantly increased the abundance of different nematode trophic groups and total nematode biomass, indicating that planted shrubs had significant bottom-up effects on soil bacteria and nematodes. Planted shrubs decreased nematode diversity, evenness, and richness, but increased nematode dominance in the plots where the abundance of exotic earthworms was not amended. By contrast, these effects of shrub presence on soil biodiversity were not found in the plots that received exotic earthworms. In addition, planted shrubs increased the total energy flux to the nematode community. By contrast, the elevated activity of exotic earthworms mitigated the increase in total energy flux to nematodes in the presence of shrubs, and increased the ratio of fungal to bacterial PLFAs. Both of these changes indicate reduced energy flux in the plots with added exotic earthworms. Nematode diversity decreased, while nematode dominance increased with increasing total energy flux to nematodes, probably because few species benefited from high energy flux. Our study indicates that exotic earthworms can maintain soil biodiversity by reducing the energy flux through soil food webs. [ABSTRACT FROM AUTHOR]

Numerous important ecosystem functions and services depend on soil biodiversity. However, little is known about the mechanisms which maintain the vast belowground biodiversity and about the filters shaping soil community composition. Yet, biotic interactions like facilitation and dispersal by animals are assumed to play a crucial role, particularly as most soil animal taxa are strongly limited in their active dispersal abilities. Here, we report on a newfound interaction of potentially high ubiquity and importance in soil communities: the endozoochorous dispersal of soil fauna by gastropods. We focus on the dispersal-limited group of oribatid mites, one of the most diverse and abundant soil animal groups. In a field survey in a German riparian forest, 73% of 40 collected slugs (Arion vulgaris) egested a total of 135 oribatid mites, belonging to 35 species. Notably, 70% of the egested mites were alive and survived the gut passage through slugs. Similar results were found for Roman snails (Helix pomatia), indicating the generality of our findings across different gastropod taxa. Complementary laboratory experiments confirmed our field observations, revealing that oribatid mites are, indeed, ingested and egested alive by slugs, and that they are able to independently escape the faeces and colonise new habitats. Our results strongly indicate that gastropods may help soil organisms to disperse within habitats, to overcome dispersal barriers, and to reach short-lived resource patches. Gastropods might even disperse whole multi-trophic micro-ecosystems, a discovery that could have profound implications for our understanding of dispersal mechanisms and the distribution of soil biodiversity. [ABSTRACT FROM AUTHOR]

Plant diversity influences many ecosystem functions including root decomposition. However, due to the presence of multiple pathways via which plant diversity may affect root decomposition, our mechanistic understanding of their relationships is limited. In a grassland biodiversity experiment, we simultaneously assessed the effects of three pathways-root litter quality, soil biota, and soil abiotic conditions-on the relationships between plant diversity (in terms of species richness and the presence/absence of grasses and legumes) and root decomposition using structural equation modeling. Our final structural equation model explained 70% of the variation in root mass loss. However, different measures of plant diversity included in our model operated via different pathways to alter root mass loss. Plant species richness had a negative effect on root mass loss. This was partially due to increased Oribatida abundance, but was weakened by enhanced root potassium (K) concentration in more diverse mixtures. Equally, grass presence negatively affected root mass loss. This effect of grasses was mostly mediated via increased root lignin concentration and supported via increased Oribatida abundance and decreased root K concentration. In contrast, legume presence showed a net positive effect on root mass loss via decreased root lignin concentration and increased root magnesium concentration, both of which led to enhanced root mass loss. Overall, the different measures of plant diversity had contrasting effects on root decomposition. Furthermore, we found that root chemistry and soil biota but not root morphology or soil abiotic conditions mediated these effects of plant diversity on root decomposition. [ABSTRACT FROM AUTHOR]

Aims: Recent studies in experimental grasslands indicated that declining plant species diversity negatively affects soil microbial communities. Here, we assessed if plant diversity effects also occur in 'real-world' grasslands. Methods: We studied the influence of fertilization, soil, and plant community characteristics on soil microbial activity (microbial biomass carbon, basal respiration) in 12 managed temperate grasslands of varying plant species richness in two subsequent years. Results: The most important variable explaining variation in microbial activity was soil water content, while positive effects of other soil characteristics (organic carbon and nitrogen concentrations) and fertilization became more important in one study year with generally moister soil conditions. Under moister conditions, fertilization also indirectly influenced soil microbial biomass C via negative effects on plant species richness, which itself increased soil microbial biomass C. Conclusion: Our results show that variation in soil microbial activity in managed grasslands involves direct effects of fertilization as well as indirect effects through changes in plant diversity and the amount of carbon and nitrogen stored in plants and soil. These results emphasize that increased nutrient inputs in grasslands entail complex changes in ecosystem processes and indicate that mechanisms driving soil microbial activity in experimental grasslands also apply to 'real-world' grasslands. [ABSTRACT FROM AUTHOR]

The magnitude and frequency of extreme weather events are predicted to increase in the future due to ongoing climate change. In particular, floods and droughts resulting from climate change are thought to alter the ecosystem functions and stability. However, knowledge of the effects of these weather events on soil fauna is scarce, although they are key towards functioning of terrestrial ecosystems. Plant species richness has been shown to affect the stability of ecosystem functions and food webs. Here, we used the occurrence of a natural flood in a biodiversity grassland experiment that was followed by a simulated summer drought experiment, to investigate the interactive effects of plant species richness, a natural flood, and a subsequent summer drought on nematode communities. Three and five months after the natural flooding, effects of flooding severity were still detectable in the belowground system. We found that flooding severity decreased soil nematode food-web structure (loss of K-strategists) and the abundance of plant feeding nematodes. However, high plant species richness maintained higher diversity and abundance of higher trophic levels compared to monocultures throughout the flood. The subsequent summer drought seemed to be of lower importance but reversed negative flooding effects in some cases. This probably occurred because the studied grassland system is well adapted to drought, or because drought conditions alleviated the negative impact of long-term soil waterlogging. Using soil nematodes as indicator taxa, this study suggests that high plant species richness can maintain soil food web complexity after consecutive environmental perturbations. [ABSTRACT FROM AUTHOR]

Aims: The passage of seeds through the earthworm gut potentially damages seeds, altering seed and seedling performances depending on seed traits. This work was conducted to study to what extent chemical and morphological seed traits determine the seed attractiveness for earthworms. Methods: We tested seed selection via the ingestion and digestion of 23 grassland plant species spanning a range of 14 morphological and chemical traits by two common earthworm species: the anecic Lumbricus terrestris and the endogeic Allolobophora chlorotica. Results: Both earthworm species ingested seeds from all plant species. A. chlorotica digested almost all ingested seeds (out of the 15 % ingested), whereas L. terrestris excreted them in varying quantities (out of the 86 % ingested), depending on plant species identity. Seed ingestion rate by L. terrestris was driven by seed oil content and earthworm initial weight. The apparent effect of seed length was explained via seed oil content. Seed digestion rate by L. terrestris was negatively impacted by seed size. Seed ingestion rate by A. chlorotica tended to be impacted by seed protein content and seed length. Conclusion: Earthworms-seed interactions depend on a variety of seed traits and earthworm identity. Thus, earthworms, via their specific feeding behavior, might facilitate or impede the regeneration of certain plant species and drive plant communities. [ABSTRACT FROM AUTHOR]

Higher plant diversity reduces nitrate leaching by complementary resource use, while its relation to leaching of other N species is unclear. We determined the effects of plant species richness, functional group richness, and the presence of specific functional groups on ammonium, dissolved organic N (DON), and total dissolved N (TDN) leaching from grassland in the first 4 years after conversion from fertilized arable land to unfertilized grassland. On 62 experimental plots in Jena, Germany, with 1-60 plant species and 1-4 functional groups (legumes, grasses, tall herbs, small herbs), nitrate, ammonium, and TDN concentrations in soil solution (0-0.3 m soil layer) were measured fortnightly during 4 years. DON concentrations were calculated by subtracting inorganic N from TDN. Nitrogen concentrations were multiplied with modeled downward water fluxes to obtain N leaching. DON leaching contributed most to TDN leaching (64 ± SD 4% of TDN). Ammonium leaching was unaffected by plant diversity. Increasing species richness decreased DON leaching in the fourth year. We attribute this finding to enhanced use of DON as a C and N source and enhanced mineralization of DON by soil microorganisms. An increase of species richness decreased TDN leaching likely driven by the complementary use of nitrate by diverse mixtures. Legumes increased DON and TDN leaching likely because of their N $$_{2}$$ -fixing ability and higher litter production. Grasses decreased TDN leaching because of more exhaustive use of nitrate and water. Our results demonstrate that increasing plant species richness decreases leaching of DON and TDN. [ABSTRACT FROM AUTHOR]

Background and aims: Soil hydraulic properties drive water distribution and availability in soil. There exists limited knowledge of how plant species diversity might influence soil hydraulic properties. Methods: We quantified the change in infiltration capacity affected by soil structural variables (soil bulk density, porosity and organic carbon content) along a gradient of soil texture, plant species richness (1, 2, 4, 8, 16 and 60) and functional group composition (grasses, legumes, small herbs, tall herbs). We conducted two infiltration measurement campaigns (May and October 2012) using a hood infiltrometer. Results: Plant species richness significantly increased infiltration capacity in the studied grasslands. Both soil porosity (or inversely bulk density) and organic carbon played an important role in mediating the plant species richness effect. Soil texture did not correlate with infiltration capacity. In spring 2012, earthworm biomass increased infiltration capacity, but this effect could not be attributed to changes in soil structural variables. Conclusions: We experimentally identified important ecological drivers of infiltration capacity, suggesting complex interactions between plant species richness, earthworms, and soil structural variables, while showing little impact of soil texture. Changes in plant species richness may thus have significant effects on soil hydraulic properties with potential consequences for surface run-off and soil erosion. [ABSTRACT FROM AUTHOR]

Common buckthorn ( Rhamnus cathartica L.) is one of the most abundant and ecologically harmful non-native plants in forests of the Upper Midwest United States. At the same time, European earthworms are invading previously glaciated areas in this region, with largely anecdotal evidence suggesting they compound the negative effects of buckthorn and influence the invasibility of these forests. Germination and seedling establishment are important control points for colonization by any species, and manipulation of the conditions influencing these life history stages may provide insight into why invasive species are successful in some environments and not others. Using a greenhouse microcosm experiment, we examined the effects of important biotic and abiotic factors on the germination and seedling establishment of common buckthorn. We manipulated light levels, leaf litter depth and earthworm presence to investigate the independent and interactive effects of these treatments on buckthorn establishment. We found that light and leaf litter depth were significant predictors of buckthorn germination but that the presence of earthworms was the most important factor; earthworms interacted with light and leaf litter to increase the number and biomass of buckthorn across all treatments. Path analysis suggested both direct and moisture-mediated indirect mechanisms controlled these processes. The results suggest that the action of earthworms may provide a pathway through which buckthorn invades forests of the Upper Midwest United States. Hence, researchers and managers should consider co-invasion of plants and earthworms when investigating invasibility and creating preemptive or post-invasion management plans. [ABSTRACT FROM AUTHOR]

Tree species interact with soil biota to impact soil organic carbon (C) pools, but it is unclear how this interaction is shaped by various ecological factors. We used multiple regression to describe how ~100 variables were related to soil organic C pools in a common garden experiment with 14 temperate tree species. Potential predictor variables included: (i) the abundance, chemical composition, and decomposition rates of leaf litter and fine roots, (ii) species richness and abundance of bacteria, fungi, and invertebrate animals in soil, and (iii) measures of soil acidity and texture. The amount of organic C in the organic horizon and upper 20 cm of mineral soil (i.e. the combined C pool) was strongly negatively correlated with earthworm abundance and strongly positively correlated with the abundance of aluminum, iron, and protons in mineral soils. After accounting for these factors, we identified additional correlations with soil biota and with litter traits. Rates of leaf litter decomposition, measured as litter mass loss, were negatively correlated with size of the combined soil organic C pool. Somewhat paradoxically, the combined soil organic C pool was also negatively related to the ratio of recalcitrant compounds to nitrogen in leaf litter. These apparent effects of litter traits probably arose because two independent components of litter 'quality' were controlling different aspects of decomposition. Leaf litter mass loss rates were positively related with leaf litter calcium concentrations, reflecting greater utilization and depolymerization of calcium-rich leaf litter by earthworms and other soil biota, which presumably led to greater proportional losses of litter C as CO or dissolved organic C. The fraction of depolymerized and metabolized litter that is ultimately lost as CO is an inverse function of microbial C use efficiency, which increases with litter nutrient concentrations but decreases with concentrations of recalcitrant compounds (e.g. lignin); thus, high ratios of recalcitrant compounds to nitrogen in leaf litter likely caused a greater fraction of depolymerized litter to be lost as CO. Existing conceptual models of soil C stabilization need to reconcile the effects of litter quality on these two potentially counteracting factors: rates of litter depolymerization and microbial C use efficiency. [ABSTRACT FROM AUTHOR]

Climate change causes species range shifts and potentially alters biological invasions. The invasion of European earthworm species across northern North America has severe impacts on native ecosystems. Given the long and cold winters in that region that to date supposedly have slowed earthworm invasion, future warming is hypothesized to accelerate earthworm invasions into yet non-invaded regions. Alternatively, warming-induced reductions in soil water content (SWC) can also decrease earthworm performance. We tested these hypotheses in a field warming experiment at two sites in Minnesota, USA by sampling earthworms in closed and open canopy in three temperature treatments in 2010 and 2012. Structural equation modeling revealed that detrimental warming effects on earthworm densities and biomass could indeed be partly explained by warming-induced reductions in SWC. The direction of warming effects depended on the current average SWC: warming had neutral to positive effects at high SWC, whereas the opposite was true at low SWC. Our results suggest that warming limits the invasion of earthworms in northern North America by causing less favorable soil abiotic conditions, unless warming is accompanied by increased and temporally even distributions of rainfall sufficient to offset greater water losses from higher evapotranspiration. [ABSTRACT FROM AUTHOR]