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Climate change will affect the way biodiversity influences the stability of plant communities. Although biodiversity, associated species asynchrony, and species stability could enhance community stability, the understanding of potential nonlinear shifts in the biodiversity–stability relationship across a wide range of aridity (measured as the aridity index, the precipitation/potential evapotranspiration ratio) gradients and the underlying mechanisms remain limited. Using an 8‐year dataset from 687 sites in Mongolia, which included 5496 records of vegetation and productivity, we found that the temporal stability of plant communities decreased more rapidly in more arid areas than in less arid areas. The result suggests that future aridification across terrestrial ecosystems may adversely affect community stability. Additionally, we identified nonlinear shifts in the effects of species richness and species synchrony on temporal community stability along the aridity gradient. Species synchrony was a primary driver of community stability, which was consistently negatively affected by species richness while being positively affected by the synchrony between C3 and C4 species across the aridity gradient. These results highlight the crucial role of C4 species in stabilizing communities through differential responses to interannual climate variations between C3 and C4 species. Notably, species richness and the synchrony between C3 and C4 species independently regulated species synchrony, ultimately affecting community stability. We propose that maintaining plant communities with a high diversity of C3 and C4 species will be key to enhancing community stability across Mongolian grasslands. Moreover, species synchrony, species stability, species richness and the synchrony between C3 and C4 species across the aridity gradient consistently mediated the impacts of aridity on community stability. Hence, strategies aimed at promoting the maintenance of biological diversity and composition will help ecosystems adapt to climate change or mitigate its adverse effects on ecosystem stability. [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]

It is well known that biodiversity positively affects ecosystem functioning, leading to enhanced ecosystem stability. However, this knowledge is mainly based on analyses using single ecosystem functions, while studies focusing on the stability of ecosystem multifunctionality (EMF) are rare. Taking advantage of a long‐term grassland biodiversity experiment, we studied the effect of plant diversity (1–60 species) on EMF over 5 years, its temporal stability, as well as multifunctional resistance and resilience to a 2‐year drought event. Using split‐plot treatments, we further tested whether a shared history of plants and soil influences the studied relationships. We calculated EMF based on functions related to plants and higher‐trophic levels. Plant diversity enhanced EMF in all studied years, and this effect strengthened over the study period. Moreover, plant diversity increased the temporal stability of EMF and fostered resistance to reoccurring drought events. Old plant communities with shared plant and soil history showed a stronger plant diversity–multifunctionality relationship and higher temporal stability of EMF than younger communities without shared histories. Our results highlight the importance of old and biodiverse plant communities for EMF and its stability to extreme climate events in a world increasingly threatened by global change. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) affects many areas of the world and is increasing globally. To date, there has been limited and inconsistent evidence regarding the consequences of ALAN for plant communities, as well as for the fitness of their constituent species. ALAN could be beneficial for plants as they need light as energy source, but they also need darkness for regeneration and growth. We created model communities composed of 16 plant species sown, exposed to a gradient of ALAN ranging from 'moonlight only' to conditions like situations typically found directly underneath a streetlamp. We measured plant community composition and its production (biomass), as well as functional traits of three plant species from different functional groups (grasses, herbs, legumes) in two separate harvests. We found that biomass was reduced by 33% in the highest ALAN treatment compared to the control, Shannon diversity decreased by 43% and evenness by 34% in the first harvest. Some species failed to establish in the second harvest. Specific leaf area, leaf dry matter content and leaf hairiness responded to ALAN. These responses suggest that plant communities will be sensitive to increasing ALAN, and they flag a need for plant conservation activities that consider impending ALAN scenarios. This article is part of the theme issue 'Light pollution in complex ecological systems'. [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]

Root‐associated fungi could play a role in determining both the positive relationship between plant diversity and productivity in experimental grasslands, and its strengthening over time. This hypothesis assumes that specialized pathogenic and mutualistic fungal communities gradually assemble over time, enhancing plant growth more in species‐rich than in species‐poor plots. To test this hypothesis, we used high‐throughput amplicon sequencing to characterize root‐associated fungal communities in experimental grasslands of 1 and 15 years of age with varying levels of plant species richness. Specifically, we tested whether the relationship between fungal communities and plant richness and productivity becomes stronger with the age of the experimental plots. Our results showed that fungal diversity increased with plant diversity, but this relationship weakened rather than strengthened over the two time points. Contrastingly, fungal community composition showed increasing associations with plant diversity over time, suggesting a gradual build‐up of specific fungal assemblages. Analyses of different fungal guilds showed that these changes were particularly marked in pathogenic fungi, whose shifts in relative abundance are consistent with the pathogen dilution hypothesis in diverse plant communities. Our results suggest that root‐associated fungal pathogens play more specific roles in determining the diversity–productivity relationship than other root‐associated plant symbionts. [ABSTRACT FROM AUTHOR]

Positive plant diversity–productivity relationships are known to be driven by complementary resource use via differences in plant functional traits. Moreover, soil properties related to nutrient availability were shown to change with plant diversity over time; however, it is not well‐understood whether and how such plant diversity‐dependent soil changes and associated changes in functional traits contribute to positive diversity–productivity relationships in the long run. To test this, we investigated plant communities of different species richness (1, 2, 6, and 9 species) in a 15‐year‐old grassland biodiversity experiment. We determined community biomass production and biodiversity effects (net biodiversity [NEs], complementarity [CEs], and selection effects [SEs]), as well as community means of plant functional traits and soil properties. First, we tested how these variables changed along the plant diversity gradient and were related to each other. Then, we tested for direct and indirect effects of plant and soil variables influencing community biomass production and biodiversity effects. Community biomass production, NEs, CEs, SEs, plant height, root length density (RLD), and all soil property variables changed with plant diversity and the presence of the dominant grass species Arrhenatherum elatius (increase except for soil pH, which decreased). Plant height and RLD for plant functional traits, and soil pH and organic carbon concentration for soil properties, were the variables with the strongest influence on biomass production and biodiversity effects. Our results suggest that plant species richness and the presence of the dominant species, A. elatius, cause soil organic carbon to increase and soil pH to decrease over time, which increases nutrient availability favoring species with tall growth and dense root systems, resulting in higher biomass production in species‐rich communities. Here, we present an additional process that contributes to the strengthening positive diversity–productivity relationship, which may play a role alongside the widespread plant functional trait‐based explanation. [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]

1. Understanding how ecosystem multifunctionality is maintained in naturally assembled communities is crucial, because human activities benefit from multiple functions and services of various ecosystems. However, the effects of aboveand below-ground biodiversity on ecosystem multifunctionality in alpine and boreal moorland ecosystems remain unclear despite their potential as global carbon sinks. 2. Here we evaluated how ecosystem multifunctionality related to primary production and carbon sequestration, which are crucial for global climate regulation, is maintained in natural systems. We disentangled the relationships between diversity and composition of plants and soil microbes (fungi and bacteria) and ecosystem multifunctionality in subalpine moorlands in northern Japan. 3. We found that microbial composition primarily regulated carbon sequestration, whereas plant taxonomic and functional composition were related to all functions considered. Plant and microbial α diversity (diversity within local communities) were not generally related to any single function, highlighting the important roles of specific plant and microbial taxa in determining ecosystem functioning. When single functions were aggregated to ecosystem multifunctionality within local communities, plant and microbial community composition rather than diversity regulated ecosystem multifunctionality. We further found that plant and bacterial taxonomic β diversity (taxonomic turnover between local communities) primarily regulated the dissimilarity of ecosystem multifunctionality between local communities. 4. Synthesis. We provide observational evidence that plant and microbial community composition rather than diversity are essential for sustaining subalpine moorland multifunctionality. Furthermore, plant and bacterial β diversity enhance the dissimilarity of moorland multifunctionality. Our study provides novel insights into biodiversity–ecosystem multifunctionality relationships occurring in nature, and helps to sustain desirable ecosystem functioning to human society. [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]

Plant–soil feedback (PSF) has gained attention as a mechanism promoting plant growth and coexistence. However, most PSF research has measured monoculture growth in greenhouse conditions. Translating PSFs into effects on plant growth in field communities remains an important frontier for PSF research. Using a 4‐year, factorial field experiment in Jena, Germany, we measured the growth of nine grassland species on soils conditioned by each of the target species (i.e., 72 PSFs). Plant community models were parameterized with or without these PSF effects, and model predictions were compared to plant biomass production in diversity–productivity experiments. Plants created soils that changed subsequent plant biomass by 40%. However, because they were both positive and negative, the average PSF effect was 14% less growth on "home" than on "away" soils. Nine‐species plant communities produced 29 to 37% more biomass for polycultures than for monocultures due primarily to selection effects. With or without PSF, plant community models predicted 28%–29% more biomass for polycultures than for monocultures, again due primarily to selection effects. Synthesis: Despite causing 40% changes in plant biomass, PSFs had little effect on model predictions of plant community biomass across a range of species richness. While somewhat surprising, a lack of a PSF effect was appropriate in this site because species richness effects in this study were caused by selection effects and not complementarity effects (PSFs are a complementarity mechanism). Our plant community models helped us describe several reasons that even large PSF may not affect plant productivity. Notably, we found that dominant species demonstrated small PSF, suggesting there may be selective pressure for plants to create neutral PSF. Broadly, testing PSFs in plant communities in field conditions provided a more realistic understanding of how PSFs affect plant growth in communities in the context of other species traits. [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]

Defaunation including invertebrate decline is one of the major consequences of anthropogenic alterations of the environment. Despite recent reports of ubiquitous invertebrate decline, the ecosystem consequences have been rarely documented. We exposed standardized plant communities grown in the iDiv Ecotron to different levels of invertebrate numbers and biomass and tracked effects on the diversity and composition of bacterial communities associated with flowers and leaves of Scorzoneroides autumnalis and Trifolium pratense using next-generation 16S rRNA gene amplicon sequencing. Our data indicate that invertebrate decline reduces bacterial richness and β -diversity and alters community composition. These effects may result from direct effects of invertebrates that may serve as dispersal agents of bacteria; or from indirect effects where animal-induced changes in the plant's phenotype shape the niches plants provide for bacterial colonizers. Because bacteria are usually not dispersal limited and because species sorting, i.e. niche-based processes, has been shown to be a dominant process in bacterial community assembly, indirect effects may be more likely. Given that a healthy microbiome is of fundamental importance for the well-being of plants, animals (including humans) and ecosystems, a loss of bacterial diversity may be a dramatic yet previously unknown consequence of current invertebrate decline. [ABSTRACT FROM AUTHOR]

Droughts can strongly affect grassland productivity and biodiversity, but responses differ widely. Nutrient availability may be a critical factor explaining this variation, but is often ignored in analyses of drought responses. Here, we used a standardized nutrient addition experiment covering 10 European grasslands to test if full‐factorial nitrogen, phosphorus, and potassium addition affected plant community responses to inter‐annual variation in drought stress and to the extreme summer drought of 2018 in Europe. We found that nutrient addition amplified detrimental drought effects on community aboveground biomass production. Drought effects also differed between functional groups, with a negative effect on graminoid but not forb biomass production. Our results imply that eutrophication in grasslands, which promotes dominance of drought‐sensitive graminoids over forbs, amplifies detrimental drought effects. In terms of climate change adaptation, agricultural management would benefit from taking into account differential drought impacts on fertilized versus unfertilized grasslands, which differ in ecosystem services they provide to society. [ABSTRACT FROM AUTHOR]

Although nitrogen (N) deposition is increasing globally, N availability still limits many organisms, such as microorganisms and mesofauna. However, little is known to which extent soil organisms rely on mineral‐derived N and whether plant community composition modifies its incorporation into soil food webs. More diverse plant communities more effectively compete with microorganisms for mineral N likely reducing the incorporation of mineral‐derived N into soil food webs. We set up a field experiment in experimental grasslands with different levels of plant species and functional group richness. We labeled soil with 15NH415NO3 and analyzed the incorporation of mineral‐derived 15N into soil microorganisms and mesofauna over 3 months. Mineral‐derived N incorporation decreased over time in all investigated organisms. Plant species richness and presence of legumes reduced the uptake of mineral‐derived N into microorganisms. In parallel, the incorporation of mineral‐derived 15N into mesofauna species declined with time and decreased with increasing plant species richness in the secondary decomposer springtail Ceratophysella sp. Effects of both plant species richness and functional group richness on other mesofauna species varied with time. The presence of grasses increased the 15N incorporation into Ceratophysella sp., but decreased it in the primary decomposer oribatid mite Tectocepheus velatus sarekensis. The results highlight that mineral N is quickly channeled into soil animal food webs via microorganisms irrespective of plant diversity. The amount of mineral‐derived N incorporated into soil animals, and the plant community properties affecting this incorporation, differed markedly between soil animal taxa, reflecting species‐specific use of food resources. Our results highlight that plant diversity and community composition alter the competition for N in soil and change the transfer of N across trophic levels in soil food webs, potentially leading to changes in soil animal population dynamics and community composition. Sustaining high plant diversity may buffer detrimental effects of elevated N deposition on soil biota. [ABSTRACT FROM AUTHOR]

As ecosystem engineers, invasive earthworms are one of the main drivers of plant community changes in North American forests previously devoid of earthworms. One explanation for these community changes is the effects of earthworms on the reproduction, recruitment, and development of plant species. However, few studies have investigated functional trait responses of native plants to earthworm invasion to explain the mechanisms underlying community changes. In a mesocosm (Ecotron) experiment, we set up a plant community composed of two herb and two grass species commonly found in northern North American forests under two earthworm treatments (presence vs. absence). We measured earthworm effects on above- and belowground plant biomass and functional traits after 3 months of experiment. Our results showed that earthworm presence did not significantly affect plant community biomass and cover. Furthermore, only four out of the fifteen above- and belowground traits measured were affected by earthworm presence. While some traits, such as the production of ramets, the carbon and nitrogen content of leaves, responded similarly between and within functional groups in the presence or absence of earthworms, we observed opposite responses for other traits, such as height, specific leaf area, and root length within some functional groups in the presence of earthworms. Plant trait responses were thus species-specific, although the two grass species showed a more pronounced response to earthworm presence with changes in their leaf traits than herb species. Overall, earthworms affected some functional traits related to resource uptake abilities of plants and thus could change plant competition outcomes over time, which could be an explanation of plant community changes observed in invaded ecosystems. [ABSTRACT FROM AUTHOR]

Understanding factors that maintain ecosystem stability is critical in the face of environmental change. Experiments simulating species loss from grassland have shown that losing biodiversity decreases ecosystem stability. However, as the originally sown experimental communities with reduced biodiversity develop, plant evolutionary processes or the assembly of interacting soil organisms may allow ecosystems to increase stability over time. We explored such effects in a long‐term grassland biodiversity experiment with plant communities with either a history of co‐occurrence (selected communities) or no such history (naïve communities) over a 4‐yr period in which a major flood disturbance occurred. Comparing communities of identical species composition, we found that selected communities had temporally more stable biomass than naïve communities, especially at low species richness. Furthermore, selected communities showed greater biomass recovery after flooding, resulting in more stable post‐flood productivity. In contrast to a previous study, the positive diversity–stability relationship was maintained after the flooding. Our results were consistent across three soil treatments simulating the presence or absence of co‐selected microbial communities. We suggest that prolonged exposure of plant populations to a particular community context and abiotic site conditions can increase ecosystem temporal stability and resilience due to short‐term evolution. A history of co‐occurrence can in part compensate for species loss, as can high plant diversity in part compensate for the missing opportunity of such adaptive adjustments. [ABSTRACT FROM AUTHOR]

The inference of pairwise competitive outcomes (PCO) and multispecies competitive ranks and intransitivity from empirical data is essential to evaluate how competition shapes plant communities. Three categories of methods, differing in theoretical background and data requirements, have been used: (a) theoretically sound coexistence theory‐based methods, (b) index‐based methods, and (c) 'process‐from‐pattern' methods. However, how they are related is largely unknown.In this study, we explored the relations between the three categories by explicitly comparing three representatives of them: (a) relative fitness difference (RFD), (b) relative yield (RY), and (c) a reverse‐engineering approach (RE). Specifically, we first conducted theoretical analyses with Lotka–Volterra competition models to explore their theoretical linkages. Second, we used data from a long‐term field experiment and a short‐term greenhouse experiment with eight herbaceous perennials to validate the theoretical findings.The theoretical analyses showed that RY or RE applied with equilibrium data indicated equivalent, or very similar, PCO respectively to RFD, but these relations became weaker or absent with data further from equilibrium. In line with this, both RY and RE converged with RFD in indicating PCO over time in the field experiment as the communities became closer to equilibrium. Moreover, the greenhouse PCO (far from equilibrium) were only similar to the field PCO of earlier rather than later years. Intransitivity was more challenging to infer because it could be reshuffled by even a small competitive shift among similar competitors. For example, the field intransitivity inferred by three methods differed greatly: no intransitivity was detected with RFD; intransitivity detected with RY and RE was poorly correlated, changed substantially over time (even after equilibrium) and failed to explain coexistence.Our findings greatly help the comparison and generalization of studies using different methods. For future studies, if equilibrium data are available, one can infer PCO and multispecies competitive ranks with RY or RE. If not, one should apply RFD with density gradient or time‐series data. Equilibria could be evaluated with T tests or standard deviations. To reliably infer intransitivity, one needs high quality data for a given method to first accurately infer PCO, especially among similar competitors. [ABSTRACT FROM AUTHOR]

Earth is experiencing a substantial loss of biodiversity at the global scale, while both species gains and losses are occurring at local and regional scales. The influence of these nonrandom changes in species distributions could profoundly affect the functioning of ecosystems and the essential services that they provide. However, few experimental tests have been conducted examining the influence of species invasions on ecosystem functioning. Even fewer have been conducted using invasive ecosystem engineers, which can have disproportionately strong influence on native ecosystems relative to their own biomass. The invasion of exotic earthworms is a prime example of an ecosystem engineer that is influencing many ecosystems around the world. In particular, European earthworm invasions of northern North American forests cause simultaneous species gains and losses with significant consequences for essential ecosystem processes like nutrient cycling and crucial services to humanity like soil erosion control and carbon sequestration. Exotic earthworms are expected to select for specific traits in communities of soil microorganisms (fast-growing bacteria species), soil fauna (promoting the bacterial energy channel), and plants (graminoids) through direct and indirect effects. This will accelerate some ecosystem processes and decelerate others, fundamentally altering how invaded forests function. This project aims to investigate ecosystem responses of northern North American forests to earthworm invasion. Using a novel, synthetic combination of field observations, field experiments, lab experiments, and meta-analyses, the proposed work will be the first systematic examination of earthworm effects on (1) plant communities and (2) soil food webs and processes. Further, (3) effects of a changing climate (warming and reduced summer precipitation) on earthworm performance will be investigated in a unique field experiment designed to predict the future spread and consequences of earthworm invasion in North America. By assessing the soil chemical and physical properties as well as the taxonomic (e.g., by the latest next-generation sequencing techniques) and functional composition of plant, soil microbial and animal communities and the processes they drive in four forests, work packages I-III take complementary approaches to derive a comprehensive and generalizable picture of how ecosystems change in response to earthworm invasion. Finally, in work package IV, meta-analyses will be used to integrate the information from work packages I-III and existing literature to investigate if earthworms cause invasion waves, invasion meltdowns, habitat homogenization, and ecosystem state shifts. Global data will be synthesized to test if the relative magnitude of effects differs from place to place depending on the functional dissimilarity between native soil fauna and exotic earthworms. Moving from local to global scale, the present proposal examines the influence of earthworm invasions on biodiversity-ecosystem functioning relationships from an aboveground-belowground perspective in natural settings. This approach is highly innovative as it utilizes the invasion by exotic earthworms as an exciting model system that links invasion biology with trait-based community ecology, global change research, and ecosystem ecology, pioneering a new generation of biodiversity-ecosystem functioning research. [ABSTRACT FROM AUTHOR]

The temporal and spatial dynamics of soil water are closely interlinked with terrestrial ecosystems functioning. The interaction between plant community properties such as species composition and richness and soil water mirrors fundamental ecological processes determining above‐ground–below‐ground feedbacks. Plant–water relations and water stress have attracted considerable attention in biodiversity experiments. Yet, although soil scientific research suggests an influence of ecosystem productivity on soil hydraulic properties, temporal changes of the soil water content and soil hydraulic properties remain largely understudied in biodiversity experiments. Thus, insights on how plant diversity—productivity relationships affect soil water are lacking.Here, we determine which factors related to plant community composition (species and functional group richness, presence of plant functional groups) and soil (organic carbon concentration) affect soil water in a long‐term grassland biodiversity experiment (The Jena Experiment).Both plant species richness and the presence of particular functional groups affected soil water content, while functional group richness played no role. The effect of species richness changed from positive to negative and expanded to deeper soil with time. Shortly after establishment, increased topsoil water content was related to higher leaf area index in species‐rich plots, which enhanced shading. In later years, higher species richness increased topsoil organic carbon, likely improving soil aggregation. Improved aggregation, in turn, dried topsoils in species‐rich plots due to faster drainage of rainwater. Functional groups affected soil water distribution, likely due to plant traits affecting root water uptake depths, shading, or water‐use efficiency. For instance, topsoils in plots containing grasses were generally drier, while plots with legumes were moister.Synthesis. Our decade‐long experiment reveals that the maturation of grasslands changes the effects of plant richness from influencing soil water content through shading effects to altering soil physical characteristics in addition to modification of water uptake depth. Functional groups affected the soil water distribution by characteristic shifts of root water uptake depth, but did not enhance exploitation of the overall soil water storage. Our results reconcile previous seemingly contradictory results on the relation between grassland species diversity and soil moisture and highlight the role of vegetation composition for soil processes. The effect of plant species richness on soil water content in the Jena Experiment changed with time after establishment, and was related at the beginning to aboveground (canopy) and later to belowground (soil organic carbon, roots) processes. In contrast, each plant functional group affected soil water distribution in a characteristic fashion that did not change with time, but varied in strength between years. Overall, the analysis suggests that recovery of soil functions after abandonment of arable farming may benefit from higher grassland diversity as a follow up land use, which likely feeds back on other ecosystem functions. [ABSTRACT FROM AUTHOR]

Abstract: Understanding how biodiversity (B) affects ecosystem functioning (EF) is essential for assessing the consequences of ongoing biodiversity changes. An increasing number of studies, however, show that environmental conditions affect the shape of BEF relationships. Here, we first use a game‐theoretic community model to reveal that a unimodal response of the BEF slope can be expected along environmental stress gradients, but also how the ecological mechanisms underlying this response may vary depending on how stress affects species interactions. Next, we analysed a global dataset of 44 experiments that crossed biodiversity with environmental conditions. Confirming our main model prediction, the effect of biodiversity on ecosystem functioning tends to be greater at intermediate levels of environmental stress, but varies among studies corresponding to differences in stress‐effects on species interactions. Together, these results suggest that increases in stress from ongoing global environmental changes may amplify the consequences of biodiversity changes. [ABSTRACT FROM AUTHOR]

The extensive use of traits in ecological studies over the last few decades to predict community functions has revealed that plant traits are plastic and respond to various environmental factors. These plant traits are assumed to predict how plants compete and capture resources. Variation in stoichiometric ratios both within and across species reflects resource capture dynamics under competition. However, the impact of local plant diversity on species‐specific stoichiometry remains poorly studied. Here, we analyze how spatial and temporal diversity in resource‐acquisition traits affects leaf elemental stoichiometry of plants (i.e. the result of resource capture) and how flexible this stoichiometry is depending on the functional composition of the surrounding community. Therefore, we assessed inter‐ and intraspecific variations of leaf carbon (C), nitrogen (N), and phosphorus (P) (and their ratios) of 20 grassland species in a large trait‐based plant diversity experiment located in Jena (Germany) by measuring leaf elemental concentrations at the species‐level along a gradient in plant trait dissimilarity. Our results show that plants showed large intra‐ and interspecific variation in leaf stoichiometry, which was only partly explained by the functional group identity (grass or herb) of the species. Elemental concentrations (N, P, but not C) decreased with plant species richness, and species tended to become more deviant from their monoculture stoichiometry with increasing trait dissimilarity in the community. These responses differed among species, some consistently increased or decreased in P and N concentrations; for other species, the negative or positive change in P and N concentrations increased with increasing trait difference between the target species and the remaining community. The strength of this relationship was significantly associated to the relative position of the species along trait gradients related to resource acquisition. Trait‐difference and trait‐diversity thus were important predictors of how species’ resource capture changed in competitive neighbourhoods. [ABSTRACT FROM AUTHOR]

Niche complementarity and competitive disparity are driving mechanisms behind plant community assembly and productivity. Consequently, there is great interest in predicting species complementarity and their competitive differences from their functional traits as dissimilar species may compete less and result in more complete use of resources., Here we assessed the role of trait dissimilarities for species complementarity and competitive disparities within an experimental gradient of plant species richness and functional trait dissimilarity. Communities were assembled using three pools of grass and forb species based on a priori knowledge of traits related to (1) above- and below-ground spatial differences in resource acquisition, (2) phenological differences or (3) both. Complementarity and competitive disparities were assessed by partitioning the overyielding in mixed species communities into species complementarity and dominance effects., Community overyielding and the underlying complementarity and competitive dominance varied strongly among the three plant species pools. Overyielding and complementarity were greatest among species that were assembled based on their variation in both spatial and phenological traits. Competitive dominance was greatest when species were assembled based on spatial resource acquisition traits alone., In communities that were assembled based on species variation in only spatial or phenological traits, greater competitive dominance was predicted by greater differences in SLA and flowering initiation respectively, while greater complementarity was predicted by greater dissimilarity in leaf area and flowering senescence respectively. Greater differences in leaf area could also be linked to greater species complementarity in communities assembled based on variation in both phenological and spatial traits, but trait dissimilarity was unrelated to competitive dominance in these communities., Our results indicate that complementarity and competitive disparity among species are both driven by trait dissimilarities. However, the identity of the traits that drives the complementarity and competitive disparity depends on the trait variation among species that comprise the community. Moreover, we demonstrate that communities assembled with the greater variation in both spatial and phenological traits show the greatest complementarity among species., A is available for this article. [ABSTRACT FROM AUTHOR]

Flooding is expected to increase in frequency and severity in the future. The ecological consequences of flooding are the combined result of species-specific plant traits and ecological context. However, the majority of past flooding research has focused on individual model species under highly controlled conditions., An early summer flooding event in a grassland biodiversity experiment in Jena, Germany, provided the opportunity to assess flooding responses of 60 grassland species in monocultures and 16-species mixtures. We examined plant biomass, species-specific traits (plant height, specific leaf area (SLA), root aerenchyma, starch content) and soil porosity., We found that, on average, plant species were less negatively affected by the flood when grown in higher-diversity plots in July 2013. By September 2013, grasses were unaffected by the flood regardless of plant diversity, and legumes were severely negatively affected regardless of plant diversity. Plants with greater SLA and more root aerenchyma performed better in September. Soil porosity was higher in higher-diversity plots and had a positive effect on plant performance., As floods become more frequent and severe in the future, growing flood-sensitive plants in higher-diversity communities and in soil with greater soil aeration may attenuate the most negative effects of flooding. [ABSTRACT FROM AUTHOR]

Stable provisioning of ecosystem functions and services is crucial for human well-being in a changing world. Two essential ecological components driving vital ecosystem functions in terrestrial ecosystems are plant diversity and soil microorganisms. In this study, we tracked soil microbial basal respiration and biomass over a time period of 12 years in a grassland biodiversity experiment (the Jena Experiment) and examined the role of plant diversity and plant functional group composition for the spatial and temporal stability of soil microbial properties (basal respiration and biomass) in bulk-soil. Spatial and temporal stability were calculated as the inverse coefficient of variation (CV−1) of soil microbial respiration and biomass measured from soil samples taken over space and time, respectively. We found that 1) plant species richness consistently increased soil microbial properties after a time lag of four years since the establishment of the experimental plots, 2) plant species richness had minor effects on the spatial stability of soil microbial properties, whereas 3) the functional composition of plant communities significantly affected spatial stability of soil microbial properties, with legumes and tall herbs reducing both the spatial stability of microbial respiration and biomass, while grasses increased the latter, and 4) the effect of plant diversity on temporal stability of soil microbial properties turned from being negative to neutral, suggesting that the recovery of soil microbial communities from former arable land-use takes more than a decade. Our results highlight the importance of plant functional group composition for the spatial and temporal stability of soil microbial properties, and hence for microbially-driven ecosystem processes, such as decomposition and element cycling, in temperate semi-natural grassland. [ABSTRACT FROM AUTHOR]

In a recent Forum paper, Wardle ( Journal of Vegetation Science, 2016) questions the value of biodiversity-ecosystem function ( BEF) experiments with respect to their implications for biodiversity changes in real world communities. The main criticism is that the previous focus of BEF experiments on random species assemblages within each level of diversity has 'limited the understanding of how natural communities respond to biodiversity loss.' He concludes that a broader spectrum of approaches considering both non-random gains and losses of diversity is essential to advance this field of research. Wardle's paper is timely because of recent observations of frequent local and regional biodiversity changes across ecosystems. While we appreciate that new and complementary experimental approaches are required for advancing the field, we question criticisms regarding the validity of BEF experiments. Therefore, we respond by briefly reiterating previous arguments emphasizing the reasoning behind random species composition in BEF experiments. We describe how BEF experiments have identified important mechanisms that play a role in real world ecosystems, advancing our understanding of ecosystem responses to species gains and losses. We discuss recent examples where theory derived from BEF experiments enriched our understanding of the consequences of biodiversity changes in real world ecosystems and where comprehensive analyses and integrative modelling approaches confirmed patterns found in BEF experiments. Finally, we provide some promising directions in BEF research. [ABSTRACT FROM AUTHOR]

Soil food webs comprise a multitude of trophic interactions that can affect the composition and productivity of plant communities. Belowground predators feeding on microbial grazers like Collembola could decelerate nutrient mineralization by reducing microbial turnover in the soil, which in turn could negatively influence plant growth. However, empirical evidences for the ecological significance of belowground predators on nutrient cycling and plant communities are scarce. Here, we manipulated predator density ( Hypoaspis aculeifer: predatory mite) with equal densities of three Collembola species as a prey in four functionally dissimilar plant communities in experimental microcosms: grass monoculture ( Poa pratensis), herb monoculture ( Rumex acetosa), legume monoculture ( Trifolium pratense), and all three species as a mixed plant community. Density manipulation of predators allowed us to test for density-mediated effects of belowground predators on Collembola and lower trophic groups. We hypothesized that predator density will reduce Collembola population causing a decrease in nutrient mineralization and hence detrimentally affect plant growth. First, we found a density-dependent population change in predators, that is, an increase in low-density treatments, but a decrease in high-density treatments. Second, prey suppression was lower at high predator density, which caused a shift in the soil microbial community by increasing the fungal: bacterial biomass ratio, and an increase of nitrification rates, particularly in legume monocultures. Despite the increase in nutrient mineralization, legume monocultures performed worse at high predator density. Further, individual grass shoot biomass decreased in monocultures, while it increased in mixed plant communities with increasing predator density, which coincided with elevated soil N uptake by grasses. As a consequence, high predator density significantly increased plant complementarity effects indicating a decrease in interspecific plant competition. These results highlight that belowground predators can relax interspecific plant competition by increasing nutrient mineralization through their density-dependent cascading effects on detritivore and soil microbial communities. [ABSTRACT FROM AUTHOR]

Plant performance is influenced by root-associated bacteria that provide important services to the host plant, such as pathogen suppression. Suppression of pathogens is known to be context-dependent and to vary between plant species, yet the significance of plant identity in shaping rhizosphere bacterial functioning in multi-species communities is largely unknown., We questioned whether the activity of a rhizosphere bacterium in producing biocontrol compounds varies with plant identity in a plant diversity gradient. We set up a gnotobiotic microcosm experiment with the model rhizosphere bacterium Pseudomonas protegens CHA0, an important biocontrol agent, and investigated the effects of plant identity and diversity on its production of biocontrol compounds. Using GFP-based reporter fusions, we assessed gene expression linked to the production of the biocontrol compounds 2,4-diacetylphloroglucinol, pyrrolnitrin and hydrogen cyanide., The expression of genes coding for biocontrol compounds was driven to a large extent by plant identity and this effect persisted along the plant species richness gradient for all tested genes. Notably, the effect of certain plant identities varied between the three tested genes, indicating a selective impact of plant species on bacterial gene expression. However, some plant species, such as Lolium perenne, consistently stimulated bacterial gene expression irrespective of the diversity of the plant community., Our results indicate that the presence of certain plant species within a community disproportionately impacts biocontrol traits expressed by rhizosphere bacteria, providing new insight into the patterns driving plant health and productivity. [ABSTRACT FROM AUTHOR]

Nutrient cycling in terrestrial ecosystems is affected by various factors such as plant diversity and insect herbivory. While several studies suggest insect herbivory to depend on plant diversity, their interacting effect on nutrient cycling is unclear. In a greenhouse experiment with grassland microcosms of one to six plant species of two functional groups (grasses and legumes), we tested the influence of plant species richness (diversity) and functional composition on plant community biomass production, insect foliar herbivory, soil microbial biomass, and nutrient concentrations in throughfall. To manipulate herbivory, zero, three or six generalist grasshoppers ( Chorthippus parallelus) were added to the plant communities. Increasing plant species richness increased shoot biomass and grasshopper performance, without significantly affecting root biomass or insect herbivory. Plant functional composition affected all of these parameters, e.g. legume communities showed the highest shoot biomass, the lowest grasshopper performance and suffered the least herbivory. Nutrient concentrations (dissolved mineral N, PO4-P, SO4-S) and pH in throughfall increased with herbivory. PO4-P and pH increases were positively affected by plant diversity, especially under high herbivore pressure. Plant functional composition affected several throughfall variables, sometimes fully explaining diversity effects. Increasing plant diversity tended to increase soil microbial biomass, but only under high herbivore pressure. Faeces quantities strongly correlated with changes in pH and PO4-P; frass may therefore be an important driver of throughfall pH and a main source of PO4-P released from living plants. Our results indicate that insect herbivory may significantly influence fast nutrient cycling processes in natural communities, particularly so in managed grasslands. [ABSTRACT FROM AUTHOR]

Land degradation reducing vegetation cover may affect the soil surface-active fauna because both aboveground and belowground invertebrates depend on complex plant communities. In this study, we evaluated the effect of land degradation and restoration on soil fauna in northeast Brazil. Sites differed in degradation status: native vegetation, moderately degraded land, highly degraded land, and land under restoration for 4 years. Araneae and Coleoptera densities were significantly higher in natural vegetation and restored land (8 ± 4 ind./trap and 41 ± 21 ind./trap, respectively) than in degraded lands (−73% and −81%, respectively). The density of Formicidae was significantly higher in natural vegetation (206 ± 181 ind./trap) than in highly degraded land (32 ± 24 ind./trap), while restored land (51 ± 10 ind./trap) and moderately degraded land (37 ± 14 ind./trap) did not differ significantly from the other degradation levels. The density of Orthoptera did not follow the aforementioned patterns, while invertebrate groups mostly had highest densities in natural land and restored land. Linear regressions showed a strong negative relation between faunal density and soil bulk density, and a positive relation with soil organic matter due to an increase in plant cover. Our results indicate that land degradation simplifies soil surface-active invertebrate communities with pronounced decreases in the density of Araneae, Coleoptera, and Formicidae, but that land restoration practices may recover the density of soil fauna even after only 4 years. Araneae, Coleoptera, and Formicidae respond sensitively to land degradation and restoration practice and are suggested as indicator groups for restoration success. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Loss of plant diversity influences essential ecosystem processes as aboveground productivity, and can have cascading effects on the arthropod communities in adjacent trophic levels. However, few studies have examined how those changes in arthropod communities can have additional impacts on ecosystem processes caused by them (e.g. pollination, bioturbation, predation, decomposition, herbivory). Therefore, including arthropod effects in predictions of the impact of plant diversity loss on such ecosystem processes is an important but little studied piece of information. In a grassland biodiversity experiment, we addressed this gap by assessing aboveground decomposer and herbivore communities and linking their abundance and diversity to rates of decomposition and herbivory. Path analyses showed that increasing plant diversity led to higher abundance and diversity of decomposing arthropods through higher plant biomass. Higher species richness of decomposers, in turn, enhanced decomposition. Similarly, species-rich plant communities hosted a higher abundance and diversity of herbivores through elevated plant biomass and C:N ratio, leading to higher herbivory rates. Integrating trophic interactions into the study of biodiversity effects is required to understand the multiple pathways by which biodiversity affects ecosystem functioning. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Decomposers and arbuscular mycorrhizal fungi (AMF) both determine plant nutrition; however, little is known about their interactive effects on plant communities. We set up a greenhouse experiment to study effects of plant competition (one- and two-species treatments), Collembola ( Heteromurus nitidus and Protaphorura armata), and AMF ( Glomus intraradices) on the performance (above- and belowground productivity and nutrient uptake) of three grassland plant species ( Lolium perenne, Trifolium pratense, and Plantago lanceolata) belonging to three dominant plant functional groups (grasses, legumes, and herbs). Generally, L. perenne benefited from being released from intraspecific competition in the presence of T. pratense and P. lanceolata. However, the presence of AMF increased the competitive strength of P. lanceolata and T. pratense against L. perenne and also modified the effects of Collembola on plant productivity. The colonization of roots by AMF was reduced in treatments with two plant species suggesting that plant infection by AMF was modified by interspecific plant interactions. Collembola did not affect total colonization of roots by AMF, but increased the number of mycorrhizal vesicles in P. lanceolata. AMF and Collembola both enhanced the amount of N and P in plant shoot tissue, but impacts of Collembola were less pronounced in the presence of AMF. Overall, the results suggest that, by differentially affecting the nutrient acquisition and performance of plant species, AMF and Collembola interactively modify plant competition and shape the composition of grassland plant communities. The results suggest that mechanisms shaping plant community composition can only be understood when complex belowground interactions are considered. [ABSTRACT FROM AUTHOR]

Background: 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 Methodology/Principal Findings: 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-tobacterial 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. Conclusions/Significance: 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. [ABSTRACT FROM AUTHOR]

The intensive discussion on the importance of biodiversity for the stability of essential processes in ecosystems has prompted a multitude of studies since the middle of the last century. Nevertheless, research has been extremely biased by focusing on the producer level, while studies on the impacts of decomposer diversity on the stability of ecosystem functions are lacking. Here, we investigate the impacts of decomposer diversity on the stability (reliability) of three important aboveground and belowground ecosystem functions: primary productivity (shoot and root biomass), litter decomposition, and herbivore infestation. For this, we analyzed the results of three laboratory experiments manipulating decomposer diversity (1-3 species) in comparison to decomposer-free treatments in terms of variability of the measured variables. Decomposer diversity often significantly but inconsistently affected the stability of all aboveground and belowground ecosystem functions investigated in the present study. While primary productivity was mainly destabilized, litter decomposition and aphid infestation were essentially stabilized by increasing decomposer diversity. However, impacts of decomposer diversity varied between plant community and fertility treatments. There was no general effect of the presence of decomposers on stability and no trend toward weaker effects in fertilized communities and legume communities. This indicates that impacts of decomposers are based on more than effects on nutrient availability. Although inconsistent impacts complicate the estimation of consequences of belowground diversity loss, underpinning mechanisms of the observed patterns are discussed. Impacts of decomposer diversity on the stability of essential ecosystem functions differed between plant communities of varying composition and fertility, implicating that human-induced changes of biodiversity and land-use management might have unpredictable effects on the processes mankind relies on. This study therefore points to the necessity of also considering soil feedback mechanisms in order to gain a comprehensive and holistic understanding of the impacts of current global change phenomena on the stability of essential ecosystem functions. [ABSTRACT FROM AUTHOR]

Background: 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. Methodology/Principal Findings: 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. Conclusions/Significance: 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. [ABSTRACT FROM AUTHOR]

Abstract: A major issue in current ecological research is the effect of biodiversity on ecosystem functioning. Although several studies reported a positive diversity – productivity relationship, the role of soil animals has been largely neglected. Nematodes are among the most widespread and important herbivores causing substantial yield losses in agriculture; however, impacts of nematodes on the diversity – productivity relationship in semi-natural plant communities have not been investigated until today. In the framework of the Jena Experiment (Thuringia, Germany) we established control and nematicide treated subplots to manipulate nematode densities on plots varying in plant species (1–16) and functional group richness (1–4). We explored the interacting effects of nematicide application and plant diversity on the main trophic groups of nematodes and on aboveground plant productivity. Nematicide application reduced the number of nematodes significantly, particularly that of plant feeders and predators. The negative impact of nematicide application on plant and bacterial feeders depended however on the diversity of the plant community. Total plant shoot biomass tended to decrease in the presence of ambient nematode densities. In detail, nematode effects varied however with plant functional group identity by reducing only the shoot biomass of herbs significantly but not that of legumes. Furthermore, the shoot biomass of grasses tended to decrease in the presence of ambient nematode densities. In contrast to total shoot biomass, nematodes decreased grass shoot biomass only in high diverse but not in low diverse plant communities. Thus, the present study for the first time highlights that nematodes likely modify the community structure und functions of semi-natural plant communities by altering the competition between plant functional groups and by attenuating the diversity – productivity relationship. [Copyright &y& Elsevier]

Abstract: Declining plant diversity potentially threatens essential ecosystem functions driven by the decomposer community, such as litter decomposition and nutrient cycling. Currently, there is no consensus on the interrelationships between plant diversity and decomposer performance and previous studies highlighted the urgent need for long-term experiments. In the Jena Experiment we investigated the long-term impacts of plant community characteristics on the structure of earthworm communities representing key decomposers in temperate grassland. We repeatedly sampled plots varying in plant species richness (1–16 species), plant functional group richness (1–4 groups), and presence of certain plant functional groups (grasses and legumes) three, four, and six years after establishment of the experiment in spring and autumn. The results show that earthworm performance is essentially driven by the presence of certain plant functional groups via a variety of mechanisms. Plant productivity (root biomass) explained most of the detrimental grass impacts (decrease in earthworm performance), while beneficial legume effects likely were linked to high quality inputs of plant residues (increase in earthworm performance). These impacts depended on the functional group of earthworms with the strongest effects on surface feeding anecic earthworms and minor effects on soil feeding endogeic species. Remarkably, effects of plant community characteristics on the composition and age structure of earthworm communities varied between seasons. Moreover, plant diversity effects reported by a former study decreased and detrimental effects of grasses increased with time. The results indicate that plant community characteristics, such as declining diversity, indeed affect the structure of earthworm communities; however, loss of key plant functional groups is likely to be more important than plant species number per se. However, in frequently disturbed ecosystems plant species richness might be important for the recovery and resilience of belowground functions. Moreover, the results accentuate the importance of long-term repeated measurements to fully appreciate the impacts of plant community composition and diversity on ecosystem properties. Single point observations may be misleading and potentially mask the complexity of above-belowground interrelationships. [Copyright &y& Elsevier]

The anthropogenic spread of exotic ecosystem engineers profoundly impacts native ecosystems. Exotic earthworms were shown to alter plant community composition of the understory of deciduous forests previously devoid of earthworms. We investigated the effect of two exotic earthworm species ( Lumbricus terrestris L. and Octolasion tyrtaeum Savigny) belonging to different ecological groups (anecic and endogeic) on the emergence of plants from the seed bank of a northern North American deciduous forest using the seedling emergence method. We hypothesized that (1) exotic earthworms change the seedling emergence from the plant seed bank, (2) L. terrestris increases the emergence of plant seedlings of the deeper soil layer but decreases that of the upper soil layer due to plant seed burial, and (3) O. tyrtaeum decreases plant seedling emergence due the damage of plant seeds. Indeed, exotic earthworms altered the emergence of plant seedlings from the seed bank and the functional composition of the established plant seedlings. Surprisingly, although L. terrestris only marginally affected seedling emergence, O. tyrtaeum changed the emergence of native plant species from the seed bank considerably. In particular, the number of emerging grass and herb seedlings were increased in the presence of O. tyrtaeum in both soil layers. Moreover, the impacts of earthworms depended on the identity of plant functional groups; herb species benefited, whereas legumes suffered from the presence of exotic earthworms. The results highlight the strong effect of invasive belowground ecosystem engineers on aboveground ecosystem characteristics and suggest fundamental changes of ecosystems by human-spread earthworm species. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of the role of decomposers in the plant diversity–productivity relationship is scarce. In the framework of the Jena Experiment, we observed regrowth of grassland plant communities varying in plant species and functional group richness three weeks after mowing. We investigated earthworm subplots and subplots with reduced earthworm density in order to explore if earthworms enhance plant regrowth and if earthworm effects depend on plant diversity. Earthworms significantly enhanced each of the plant regrowth parameters (plant coverage and maximum and average height of the vegetation) suggesting that particularly fast growing species, such as grasses, benefit from earthworm activity. However, the average height of the vegetation was not affected in 16-species mixtures suggesting compensation of the impact of earthworms on plant regrowth in complex plant communities. [Copyright &y& Elsevier]

Diversity is one major factor driving plant productivity in temperate grasslands. Although decomposers like earthworms are known to affect plant productivity, interacting effects of plant diversity and earthworms on plant productivity have been neglected in field studies. We investigated in the field the effects of earthworms on plant productivity, their interaction with plant species and functional group richness, and their effects on belowground plant competition. In the framework of the Jena Experiment we determined plant community productivity (in 2004 and 2007) and performance of two phytometer plant species [ Centaurea jacea (herb) and Lolium perenne (grass); in 2007 and 2008] in a plant species (from one to 16) and functional group richness gradient (from one to four). We sampled earthworm subplots and subplots with decreased earthworm density and reduced aboveground competition of phytometer plants by removing the shoot biomass of the resident plant community. Earthworms increased total plant community productivity (+11%), legume shoot biomass (+35%) and shoot biomass of the phytometer C. jacea (+21%). Further, phytometer performance decreased, i.e. belowground competition increased, with increasing plant species and functional group richness. Although single plant functional groups benefited from higher earthworm numbers, the effects did not vary with plant species and functional group richness. The present study indicates that earthworms indeed affect the productivity of semi-natural grasslands irrespective of the diversity of the plant community. Belowground competition increased with increasing plant species diversity. However, belowground competition was modified by earthworms as reflected by increased productivity of the phytometer C. jacea. Moreover, particularly legumes benefited from earthworm presence. Considering also previous studies, we suggest that earthworms and legumes form a loose mutualistic relationship affecting essential ecosystem functions in temperate grasslands, in particular decomposition and plant productivity. Further, earthworms likely alter competitive interactions among plants and the structure of plant communities by beneficially affecting certain plant functional groups. [ABSTRACT FROM AUTHOR]

Summary: The soil seed bank functions to escape unfavourable environmental conditions and seed predation. Anecic earthworms are increasingly recognised as important dispersers and predators of plant seeds. In contrast, the role of the usually more abundant endogeic earthworms which live and feed in the soil on plant seeds is largely unknown. We tested whether (A) endogeic earthworms (Aporrectodea rosea, Allolobophora chlorotica, Octolasion tyrtaeum, Aporrectodea caliginosa) ingest and digest grassland plant seeds (Phleum pratense, Bellis perennis, Trifolium repens, Poa trivialis, Plantago lanceolata, Medicago varia), (B) the passage of seeds through the gut of endogeic earthworms modifies seed germination, and (C) excreta (mucus and casts) of endogeic earthworms modify seed germination. As a reference effects of the well-studied anecic species Lumbricus terrestris were determined. Endogeic earthworms ingested and digested all of the studied plant seeds; however, both ingestion and digestion were earthworm and plant species specific. Moreover, passage through the gut of endogeic earthworms and their excreta modified plant seed germination (gut passage: B. perennis; excreta: Ph. pratense and Pl. lanceolata). The results indicate that endogeic earthworms may strongly impact the composition of the soil seed bank and, consequently, plant community assembly via direct and indirect effects on plant seeds. Since post-dispersal seed predation is a key factor for the structure of plant communities, with the effect on seed survival potentially exceeding that of pre-dispersal predation, seed predation and changes in germination of seeds by endogeic earthworm species is likely to drive plant community composition. [Copyright &y& Elsevier]

Invasions of natural communities by non-indigenous species threaten native biodiversity and are currently rated as one of the most important global-scale environmental problems. The mechanisms that make communities resistant to invasions and drive the establishment success of seedlings are essential both for management and for understanding community assembly and structure. Especially in grasslands, anecic earthworms are known to function as ecosystem engineers, however, their direct effects on plant community composition and on the invasibility of plant communities via plant seed burial, ingestion and digestion are poorly understood. In a greenhouse experiment we investigated the impact of Lumbricus terrestris, plant functional group identity and seed size of plant invader species and plant functional group of the established plant community on the number and biomass of plant invaders. We set up 120 microcosms comprising four plant community treatments, two earthworm treatments and three plant invader treatments containing three seed size classes. Earthworm performance was influenced by an interaction between plant functional group identity of the established plant community and that of invader species. The established plant community and invader seed size affected the number of invader plants significantly, while invader biomass was only affected by the established community. Since earthworm effects on the number and biomass of invader plants varied with seed size and plant functional group identity they probably play a key role in seedling establishment and plant community composition. Seeds and germinating seedlings in earthworm burrows may significantly contribute to earthworm nutrition, but this deserves further attention. Lumbricus terrestris likely behaves like a ‘farmer’ by collecting plant seeds which cannot directly be swallowed or digested. Presumably, these seeds are left in middens and become eatable after partial microbial decay. Increased earthworm numbers in more diverse plant communities likely contribute to the positive relationship between plant species diversity and resistance against invaders. [ABSTRACT FROM AUTHOR]

Abstract: Anecic earthworm species function as ecosystem engineers by structuring the soil environment, incorporating large amounts of litter and seeds into soil and, thereby influence the composition of plant communities. The aim of the present greenhouse experiment was to investigate the effects of three apparently anecic earthworm species on wheat seed burial, seedling establishment, wheat growth and litter incorporation. The three species differed substantially in their behavior and effect on plant establishment. Aporrectodea longa did not incorporate litter into the soil while Lumbricus terrestris (−69%) and Lumbricus rubellus friendoides (−75%) reduced the litter layer considerably during 9 weeks of incubation. Moreover, L. terrestris and L. rubellus friendoides buried more wheat seeds than A. longa. Fewer seeds germinated when buried by A. longa compared to L. terrestris. The behavior of L. terrestris and L. rubellus friendoides was characteristic for anecic earthworm species whereas that of A. longa rather resembled that of endogeic species. The present study is the first experimental evidence for anecic behavior in L. rubellus friendoides. [Copyright &y& Elsevier]

Locally, plant species richness supports many ecosystem functions. Yet, the mechanisms driving these often‐positive biodiversity–ecosystem functioning relationships are not well understood. Spatial resource partitioning across vertical resource gradients is one of the main hypothesized causes for enhanced ecosystem functioning in more biodiverse grasslands. Spatial resource partitioning occurs if species differ in where they acquire resources and can happen both above‐ and belowground. However, studies investigating spatial resource partitioning in grasslands provide inconsistent evidence. We present the results of a meta‐analysis of 21 data sets from experimental species‐richness gradients in grasslands. We test the hypothesis that increasing spatial resource partitioning along vertical resource gradients enhances ecosystem functioning in diverse grassland plant communities above‐ and belowground. To test this hypothesis, we asked three questions. (1) Does species richness enhance biomass production or community resource uptake across sites? (2) Is there evidence of spatial resource partitioning as indicated by resource tracer uptake and biomass allocation above‐ and belowground? (3) Is evidence of spatial resource partitioning correlated with increased biomass production or community resource uptake? Although plant species richness enhanced community nitrogen and potassium uptake and biomass production above‐ and belowground, we found that plant communities did not meet our criteria for spatial resource partitioning, though they did invest in significantly more aboveground biomass in higher canopy layers in mixture relative to monoculture. Furthermore, the extent of spatial resource partitioning across studies was not positively correlated with either biomass production or community resource uptake. Our results suggest that spatial resource partitioning across vertical resource gradients alone does not offer a general explanation for enhanced ecosystem functioning in more diverse temperate grasslands. [ABSTRACT FROM AUTHOR]

Although diversity‐dependent plant–soil feedbacks (PSFs) may contribute significantly to plant diversity effects on ecosystem functioning, the influences of underlying abiotic and biotic mechanistic pathways have been little explored to date. Here, we assessed such pathways with a PSF experiment using soil conditioned for ≥12 yr from two grassland biodiversity experiments. Model plant communities differing in plant species and functional group richness (current plant diversity treatment) were grown in soils conditioned by plant communities with either low‐ or high‐diversity (soil history treatment). Our results indicate that plant diversity can modify plant productivity through both diversity‐mediated plant–plant and plant–soil interactions, with the main driver (current plant diversity or soil history) differing with experimental context. Structural equation modeling suggests that the underlying mechanisms of PSFs were explained to a significant extent by both abiotic and biotic pathways (specifically, soil nitrogen availability and soil nematode richness). Thus, effects of plant diversity loss on plant productivity may persist or even increase over time because of biotic and abiotic soil legacy effects. [ABSTRACT FROM AUTHOR]

Abstract: Declining biodiversity is one of the most important aspects of anthropogenic global change phenomena, but the implications of plant species loss for soil decomposers are little understood. We used the experimental grassland community of the Jena Experiment to assess the response of density and diversity of Collembola to varying plant species richness, plant functional group richness and plant functional group identity. We sampled the experimental plots in spring and autumn four years after establishment of the experimental plant communities. Collembola density and diversity significantly increased with plant species and plant functional group richness highlighting the importance of the singular hypothesis for soil invertebrates. Generally, grasses and legumes beneficially affected Collembola density and diversity, whereas effects of small herbs usually were detrimental. These impacts were largely consistent in spring and autumn. By contrast, in the presence of small herbs the density of hemiedaphic Collembola and the diversity of Isotomidae increased in spring whereas they decreased in autumn. Beneficial impacts of plant diversity as well as those of grasses and legumes were likely due to increased root and microbial biomass, and elevated quantity and quality of plant residues serving as food resources for Collembola. By contrast, beneficial impacts of small herbs in spring probably reflect differences in microclimatic conditions, and detrimental effects in autumn likely were due to low quantity and quality of resources. The results point to an intimate relationship between plants and the diversity of belowground biota, even at small spatial scales, contrasting the findings of previous studies. The pronounced response of soil animals in the present study was presumably due to the fact that plant communities had established over several years. As decomposer invertebrates significantly impact plant performance, changes in soil biota density and diversity are likely to have major feedbacks on plant community productivity and composition. [Copyright &y& Elsevier]

Abstract: There is increasing evidence that direct interactions between earthworms and seeds impact the assembly of plant communities. However, effects of earthworms of different ecological groups and their interactions on plant germination and establishment are little known. We set up a full-factorial greenhouse experiment in order to explore impacts of different ecological groups of earthworms (epigeic, endogeic and anecic) on the establishment of seedlings. The three ecological groups of earthworms affected seedling establishment in an interactive way with the effects varying in time. While anecic earthworms detrimentally affected the number of established seedlings, impacts of epigeic and endogeic species depended on the presence of earthworms belonging to other ecological groups. Impacts of anecic earthworms were more significant and consistent than those of epigeic and endogeic ones pointing to the dominance of the effect of anecic earthworms for seedling establishment. The initial positive effect of the combined presence of epigeic and endogeic earthworms compared to treatments with only endogeic and only anecic earthworms was likely due to the acceleration of seed germination and elevated nutrient availability for seedlings in earthworm casts. By contrast, reduced numbers of seedlings in presence of both epigeic and endogeic earthworms compared to the control treatment might have been due to seedling predation after the litter layer had disappeared. The results extend current knowledge on interactions between earthworms and seeds by showing that, in addition to anecic species, also epigeic and endogeic species influence seedling establishment with their effect depending on the presence of anecic species. Moreover, the results indicate that impacts of earthworms vary with the developmental stage of seedlings highlighting the importance of interactions between earthworms and seeds. [ABSTRACT FROM AUTHOR]

It is now well established that biodiversity plays an important role in determining ecosystem functioning and its stability over time. A possible mechanism for this positive effect of biodiversity is that more diverse plant communities have a greater capacity to respond to environmental changes through shifts in species dominance and composition. In our study, we utilized data from five long-term grassland biodiversity experiments located in North America (three studies) and Central Europe (two studies), in which plant species richness and global change drivers were manipulated simultaneously. The global change drivers included warming, drought, elevated atmospheric CO2 concentrations, elevated N inputs, or intensive management. Across drivers, functional change over time was significantly greater for communities of high plant diversity than that of low diversity because of a higher functional and phylogenetic richness and mostly associated with a dominance by species with a 'slow and tall' strategy. Community functional shifts in response to global change drivers were, however, relatively weak and mostly not influenced by diversity. The exception to this was warming, where diverse communities showed stronger shifts than species-poor communities. Our results confirm the hypothesis that diverse communities have a greater capacity for functional change than species-poor communities, particularly in their successional dynamics, but also potentially in their responses to environmental change. This capacity could underlie the positive biodiversity-stability relationship and buffer ecosystem responses to environmental change. [ABSTRACT FROM AUTHOR]