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Global change drivers, such as anthropogenic nutrient inputs, are increasing globally. Nutrient deposition simultaneously alters plant biodiversity, species composition and ecosystem processes like aboveground biomass production. These changes are underpinned by species extinction, colonisation and shifting relative abundance. Here, we use the Price equation to quantify and link the contributions of species that are lost, gained or that persist to change in aboveground biomass in 59 experimental grassland sites. Under ambient (control) conditions, compositional and biomass turnover was high, and losses (i.e. local extinctions) were balanced by gains (i.e. colonisation). Under fertilisation, the decline in species richness resulted from increased species loss and decreases in species gained. Biomass increase under fertilisation resulted mostly from species that persist and to a lesser extent from species gained. Drivers of ecological change can interact relatively independently with diversity, composition and ecosystem processes and functions such as aboveground biomass due to the individual contributions of species lost, gained or persisting. EEA Santa Cruz Fil: Ladouceur, Emma. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Ladouceur, Emma. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; Alemania Fil: Ladouceur, Emma. University of Leipzig. Department of Biology; Alemania Fil: Ladouceur, Emma. Martin Luther University Halle-Wittenberg. Institute of Computer Science; Alemania Fil: Blowes, Shane A. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Blowes, Shane A. Martin Luther University Halle-Wittenberg. Institute of Computer Science; Alemania Fil: Chase, Jonathan M. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Chase, Jonathan M. Martin Luther University Halle-Wittenberg. Institute of Computer Science; Alemania Fil: Clark, Adam T. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Clark, Adam T. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; Alemania Fil: Clark, Adam T. Karl-Franzens University of Graz. Institute of Biology; Austria. Fil: Garbowski, Magda. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Garbowski, Magda. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; Alemania Fil: Alberti, Juan. Universidad Nacional de Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Laboratorio de Ecología. Mar del Plata; Argentina. Fil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Arnillas, Carlos Alberto. University of Toronto. Department of Physical and Environmental Sciences; Canadá. Fil: Bakker, Jonathan D. University of Washington. School of Environmental and Forest Sciences; Estados Unidos Fil: Barrio, Isabel C. Agricultural University of Iceland. Faculty of Environmental and Forest Sciences; Islandia Fil: Bharath, Siddharth. Atria University; India. Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina. Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Harpole, Stanley. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Harpole, Stanley. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; Alemania Martin Luther University Halle-Wittenberg. Institute of Computer Science; Alemania

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.

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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., Plant–soil feedbacks have gained attention as a mechanism of plant growth and coexistence, yet most plant–soil feedback research continues to be performed in greenhouse conditions. At the end of a 4‐year field experiment, plants created soils that changed subsequent plant growth by 37%, yet these relatively large effects had little effect on plant community growth because some feedbacks were positive and others negative and because feedbacks for the dominant species were small. Research highlights the need to test the consequences of plant–soil feedbacks in plant communities.

Seed removal can result in either seed predation or dispersal and is therefore an indicator of important ecosystem functions. To better understand how these variable processes are affected by environmental changes, rapid and reliable assessments with high temporal and spatial replication are needed. We address this need by testing the application of a rapid ecosystem function assessment (REFA) method to investigate seed removal in habitats with differing land use intensity. We recorded seed removal hourly over eight hours at 301 sites in five habitat types in three urban regions in Germany. We calculated seed removal rates per sampling period, traditionally used in seed removal studies, as well as instantaneous seed removal probabilities based on hourly sampling. Across regions, seed removal probabilities and rates were lowest in arable fields, a habitat type with high land-use intensity. Except in urban sealed areas, temperature had a negative effect on seed removal. Additional Cox hazard regressions suggest invertebrates as the main seed removing animals in arable fields, whereas vertebrates were likely removers in other habitat types. We confirm that seed removal is strongly negatively affected by human disturbance, indicating that the tested method is appropriate in different settings. We were able to recognize patterns in highly variable data and the method also has the advantages of low cost, high replication and high temporal resolution. However, there is a trade-off between the high temporal-resolution of instantaneous seed removal probabilities and the sampling effort, but adjustments in the standardized setup can be made depending on the study. To further utilize the extensive data collection in the REFA method, we propose to combine instantaneous seed removal probabilities, seed removal rates and Cox hazard regressions of seed removal to provide complementary information on the extent and temporal patterns of seed removal and indications about potential seed removing guilds. Keywords: Seed predation, seed dispersal, seed removal, granivore, REFA

A large body of research shows that biodiversity loss can reduce ecosystem functioning. However, much of the evidence for this relationship is drawn from biodiversity-ecosystem functioning experiments in which biodiversity loss is simulated by randomly assembling communities of varying species diversity, and ecosystem functions are measured. This random assembly has led some ecologists to question the relevance of biodiversity experiments to real-world ecosystems, where community assembly or disassembly may be non-random and influenced by external drivers, such as climate, soil conditions or land use. Here, we compare data from real-world grassland plant communities with data from two of the largest and longest-running grassland biodiversity experiments (the Jena Experiment in Germany and BioDIV in the United States) in terms of their taxonomic, functional and phylogenetic diversity and functional-trait composition. We found that plant communities of biodiversity experiments cover almost all of the multivariate variation of the real-world communities, while also containing community types that are not currently observed in the real world. Moreover, they have greater variance in their compositional features than their real-world counterparts. We then re-analysed a subset of experimental data that included only ecologically realistic communities (that is, those comparable to real-world communities). For 10 out of 12 biodiversity-ecosystem functioning relationships, biodiversity effects did not differ significantly between the full dataset of biodiversity experiments and the ecologically realistic subset of experimental communities. Although we do not provide direct evidence for strong or consistent biodiversity-ecosystem functioning relationships in real-world communities, our results demonstrate that the results of biodiversity experiments are largely insensitive to the exclusion of unrealistic communities and that the conclusions drawn from biodiversity experiments are generally robust. By comparing data from real-world grassland communities with data from two of the longest-running grassland biodiversity-ecosystem functioning experiments, the authors show that conclusions derived from experimental systems are robust to the removal of unrealistic experimental communities., Nature Ecology & Evolution, 4 (11), ISSN:2397-334X

Knowledge from agriculture and ecological field studies suggests that plant monocultures lose productivity over time, but the drivers underlying the long‐term performance of monocultures of grassland species are not completely understood. We examined the performance of 60 grassland species growing in monoculture for 12 years in a biodiversity experiment (Jena Experiment) and studied three groups of biotic drivers potentially affecting plant performance in monocultures over time: 1) soil biota (nematode communities, arbuscular mycorrhizal fungi), 2) leaf traits related to leaf economics spectrum, and 3) plant life‐cycle characteristics related to buffered population growth (viable seeds in topsoil, seedling density, seed survival). Monocultures of 15 out of 60 species increased productivity, while monocultures of the remaining 45 species showed slight to strong losses of productivity over time, resulting in zero biomass in 15 species. All three biotic drivers were related to the varying long‐term performance of monocultures. Their combined influence on monoculture performance could be interpreted as a tradeoff between ‘fast’ versus ‘slow’ life strategies. ‘Fast’ species showed rapid resource use and little buffering of population growth through a viable seed bank, which led to high biomass production in young monocultures but a consecutive loss of biomass production over time. ‘Slow’ species were characterized by positive nematode effects (high abundance of predatory nematodes), conservative use of resources, and a viable seed bank with high recruitment success resulting in gradually increasing productivity over time. In summary, our study highlights the importance of studying long‐term field monocultures to investigate the complex role of different biotic drivers responsible for productivity changes over time. These insights provide an essential baseline for estimating biodiversity effects on productivity as well as to understand and predict long‐term performance of plant populations.

1- Plant damage by invertebrate herbivores and pathogens influences the dynamics of grassland ecosystems, but anthropogenic changes in nitrogen and phosphorus availability can modify these relationships. 2- Using a globally distributed experiment, we describe leaf damage on 153 plant taxa from 27 grasslands worldwide, under ambient conditions and with experimentally elevated nitrogen and phosphorus. 3- Invertebrate damage significantly increased with nitrogen addition, especially in grasses and non-leguminous forbs. Pathogen damage increased with nitrogen in grasses and legumes but not forbs. Effects of phosphorus were generally weaker. Damage was higher in grasslands with more precipitation, but climatic conditions did not change effects of nutrients on leaf damage. On average, invertebrate damage was relatively higher on legumes and pathogen damage was relatively higher on grasses. Community-weighted mean damage reflected these functional group patterns, with no effects of N on community-weighted pathogen damage (due to opposing responses of grasses and forbs) but stronger effects of N on community-weighted invertebrate damage (due to consistent responses of grasses and forbs). 4- Synthesis. As human-induced inputs of nitrogen and phosphorus continue to increase, understanding their impacts on invertebrate and pathogen damage becomes increasingly important. Our results demonstrate that eutrophication frequently increases plant damage and that damage increases with precipitation across a wide array of grasslands. Invertebrate and pathogen damage in grasslands is likely to increase in the future, with potential consequences for plant, invertebrate and pathogen communities, as well as the transfer of energy and nutrients across trophic levels. EEA Santa Cruz Fil: Ebeling, Anne. University of Jena. Institute of Ecology and Evolution; Alemania Fil: Strauss, Alex T. University of Minnesota. Department of Ecology, Evolution, and Behavior; Estados Unidos Fil: Strauss, Alex T. University of Georgia. Odum School of Ecology; Estados Unidos Fil: Adler, Peter B. Utah State University. Department of Wildland Resources and the Ecology Center; Estados Unidos Fil: Arnillas, Carlos Alberto. University of Toronto —Scarborough. Department of Physical and Environmental Sciences; Canadá Fil: Barrio, Isabel C. Agricultural University of Iceland. Faculty of Environmental and Forest Sciences; Islandia Fil: Biederman, Lori A. Iowa State University. Department of Ecology, Evolution, and Organismal Biology; Estados Unidos Fil. Borer, Elizabeth T. University of Minnesota. Department of Ecology, Evolution, and Behavior; Estados Unidos Fil: Bugalho, Miguel N. University of Lisbon. Centre for Applied Ecology (CEABN-InBIO). School of Agriculture; Portugal. Fil: Caldeira, Maria C. University of Lisbon. Forest Research Centre. School of Agriculture; Portugal. Fil: Cadotte, Marc W. University of Toronto Scarborough. Department of Biological Sciences; Canadá Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina. Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Blumenthal, Dana M. USDA-ARS, Rangeland Resources & Systems Research Unit; Estados Unidos

Fertilisation experiments have demonstrated that nutrient availability is a key determinant of biomass production and carbon sequestration in grasslands. However, the influence of nutrients in explaining spatial variation in grassland biomass production has rarely been assessed. Using a global dataset comprising 72 sites on six continents, we investigated which of 16 soil factors that shape nutrient availability associate most strongly with variation in grassland aboveground biomass. Climate and N deposition were also considered. Based on theory-driven structural equation modelling, we found that soil micronutrients (particularly Zn and Fe) were important predictors of biomass and, together with soil physicochemical properties and C:N, they explained more unique variation (32%) than climate and N deposition (24%). However, the association between micronutrients and biomass was absent in grasslands limited by NP. These results highlight soil properties as key predictors of global grassland biomass production and point to serial co-limitation by NP and micronutrients.

Species‐rich plant communities can induce unique soil biotic legacy effects through changing the abundance and composition of soil biota. These soil legacy effects can cause feedbacks to influence plant performance. In addition, soil biota can induce (defensive) secondary metabolites in shoots and roots and thus affect plant–herbivore interactions. We hypothesize that plant diversity‐driven soil biotic legacy effects elicit changes in the shoot and root metabolome. We tested this hypothesis by establishing an experiment with four plant species. We grew plants in a sterile substrate inoculated with soil conditioned by different plant species communities: (a) monocultures of either of the four species, (b) the four species in a mixture, (c) an eight species mixture including all four species or (d) a sterile inoculum. After at least 8 weeks in the field, we estimated shoot herbivory. At the same time, we took root and shoot samples for metabolomics analyses by liquid chromatography quadrupole time‐of‐flight mass spectrometry. We found that shoot and root metabolomes of all plants grown in sterile soil differed significantly from those grown in living soil. The plant metabolomes in living soils differed by species and tissue. Across all species, shoots displayed a greater richness of secondary metabolites than roots. The richness of secondary metabolites differed by species and among living soils. The conditioning species richness significantly affected the Shannon diversity of secondary metabolites in Centaurea jacea. Shoot herbivory positively correlated with the richness and Shannon diversity of secondary metabolites in Leucanthemum vulgare. We detected multiple metabolites that together explained up to 88% of the variation in herbivory in the shoots of C. jacea and Plantago lanceolata. Synthesis.

Identifying to what degree inherent characteristics of plant species and their variation in response to their environment regulate the temporal stability of plant populations is important to understand patterns of species coexistence and the stability of ecosystems. Longevity is a key characteristic of plant life history and an important component of demographic storage, but age is usually unknown for herbaceous species. In a 12-year-old biodiversity experiment (Jena Experiment) comprising 80 grassland communities with six levels of plant species richness (1, 2, 4, 8, 16 and 60 species) and four levels of functional groups richness (1, 2, 3 and 4 functional groups), we studied populations of 38 dicotyledonous forb species (N = 1,683 plant individuals). The sampled individuals represented three plant functional groups (legumes, small herbs and tall herbs) and two different growth forms (species with long-lived primary roots and clonal species with rhizomes/stolons). We assessed the age of plant individuals by means of growth ring analysis and related the age of plant populations to their temporal stability in terms of peak biomass production. On average, plant species richness did not affect the mean age of the populations or the maximum age of individuals found in a population. Age of herbs with taproots increased and age of herbs with clonal growth decreased with increasing species richness, cancelling out each other when growth forms were analysed together. Mean population age was lowest for small herbs and highest for tall herbs, while legumes had an intermediate population age. Herbs with a taproot were on average older than herbs with a rhizome. Across all species-richness levels, populations with older individuals were more stable in terms of biomass production over time. Synthesis. Our study shows for the first time across multiple species that the longevity of forbs is affected by the diversity of the surrounding plant community, and that plant longevity as an important component of demographic storage increases the temporal stability of populations of grassland forb species.

Earth is home to over 350,000 vascular plant species that differ in their traits in innumerable ways. A key challenge is to predict how natural or anthropogenically driven changes in the identity, abundance and diversity of co-occurring plant species drive important ecosystem-level properties such as biomass production or carbon storage. Here, we analyse the extent to which 42 different ecosystem properties can be predicted by 41 plant traits in 78 experimentally manipulated grassland plots over 10 years. Despite the unprecedented number of traits analysed, the average percentage of variation in ecosystem properties jointly explained was only moderate (32.6%) within individual years, and even much lower (12.7%) across years. Most other studies linking ecosystem properties to plant traits analysed no more than six traits and, when including only six traits in our analysis, the average percentage of variation explained in across-year levels of ecosystem properties dropped to 4.8%. Furthermore, we found on average only 12.2% overlap in significant predictors among ecosystem properties, indicating that a small set of key traits able to explain multiple ecosystem properties does not exist. Our results therefore suggest that there are specific limits to the extent to which traits per se can predict the long-term functional consequences of biodiversity change, so that data on additional drivers, such as interacting abiotic factors, may be required to improve predictions of ecosystem property levels.

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 (naive 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 naive 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.

The diversity of primary producers strongly affects the structure and diversity of species assemblages at other trophic levels. However, limited knowledge exists of how plant diversity effects at small spatial scales propagate to consumer communities at larger spatial scales. We assessed arthropod community β and γ-diversity in response to experimentally manipulated plant community richness in two long-term grassland biodiversity experiments (Jena, Germany and Cedar Creek, USA) replicated over two years. We calculated arthropod species turnover among all plot combinations (β-diversity), and accumulated number of arthropod species occurring on (1) all pairwise plot combinations and (2) 40 randomly selected six-plot combinations (γ-diversity). The components of arthropod diversity were tested against two measures of plant diversity, namely average plant α-diversity ( PSR ¯ ) and the average difference in plant α-diversity between plots (ΔPSR). Whereas PSR ¯ points to the overall importance of plant α-diversity for arthropod community turnover and diversity on a larger scale, ΔPSR represents the role of habitat heterogeneity. We demonstrate that arthropod γ-diversity is supported by high, homogeneous plant α-diversity, despite lower arthropod β-diversity among high- compared to low-diversity plant communities. We also show that, in six-plot combinations, average plant α-diversity has a positive influence on arthropod γ-diversity only when homogeneity in plant α-diversity is also high. Varying heterogeneity in six-plot combinations showed that combinations consisting solely of plots with an intermediate level of plant α-diversity support a higher number of arthropod species compared to combinations that contain a mix of high- and low-diversity plots. In fact, equal levels of arthropod diversity were found for six-plot combinations with only intermediate or high plant α-diversity, due to saturating benefits of local and larger-scale plant diversity for higher trophic levels. Our results, alongside those of recent observational studies, strongly suggest that maintaining high α-diversity in plant communities is important for conserving multiple components of arthropod diversity. As arthropods carry out a range of essential ecosystem functions, such as pollination and natural pest-control, our findings provide crucial insight for effective planning of human-dominated landscapes to maximize both ecological and economic benefits in grassland systems.

Contains fulltext : 217065.pdf (Publisher’s version ) (Open Access) Abstract 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.

Biodiversity-ecosystem function experiments test how species diversity influences fundamental ecosystem processes. Historically, arthropod driven functions, such as herbivory and pest-control, have been thought to be influenced by direct and indirect associations among species. Although a number of studies have evaluated how plant diversity affects arthropod communities and arthropod-mediated ecosystem processes, it remains unclear whether diversity effects on arthropods are sufficiently consistent over time such that observed responses can be adequately predicted by classical hypotheses based on associational effects. By combining existing results from a long-term grassland biodiversity experiment (Jena Experiment) with new analyses, we evaluate the consistency of consumer responses within and across taxonomic, trophic, and trait-based (i.e. vertical stratification) groupings, and we consider which changes in arthropod community composition are associated with changes in consumer-mediated ecosystem functions. Overall, higher plant species richness supported more diverse and complex arthropod communities and this pattern was consistent across multiple years. Vegetation-associated arthropods responded more strongly to changes in plant species richness than ground-dwelling arthropods. Additionally, increases in plant species richness were associated with shifts in the species-abundance distributions for many, but not all taxa. For example, highly specialized consumers showed a decrease in dominance and an increase in the number of rare species with increasing plant species richness. Most ecosystem processes investigated responded to increases in plant species richness in the same way as the trophic group mediating the process, e.g. both herbivory and herbivore diversity increase with increasing plant species richness. In the Jena Experiment and other studies, inconsistencies between predictions based on classic hypotheses of associational effects and observed relationships between plant species richness and arthropod diversity likely reflect the influence of multi-trophic community dynamics and species functional trait distributions. Future research should focus on testing a broader array of mechanisms to unravel the biological processes underlying the biodiversity-ecosystem functioning relationships.

Biodiversity ensures ecosystem functioning and provisioning of ecosystem services, but it remains unclear how biodiversity-ecosystem multifunctionality relationships depend on the identity and number of functions considered. Here, we demonstrate that ecosystem multifunctionality, based on 82 indicator variables of ecosystem functions in a grassland biodiversity experiment, increases strongly with increasing biodiversity. Analysing subsets of functions showed that the effects of biodiversity on multifunctionality were stronger when more functions were included and that the strength of the biodiversity effects depended on the identity of the functions included. Limits to multifunctionality arose from negative correlations among functions and functions that were not correlated with biodiversity. Our findings underline that the management of ecosystems for the protection of biodiversity cannot be replaced by managing for particular ecosystem functions or services and emphasize the need for specific management to protect biodiversity. More plant species from the experimental pool of 60 species contributed to functioning when more functions were considered. An individual contribution to multifunctionality could be demonstrated for only a fraction of the species.

Changes to primary producer diversity can cascade up to consumers and affect ecosystem processes. Although the effect of producer diversity on higher trophic groups have been studied, these studies often quantify taxonomy-based measures of biodiversity, like species richness, which do not necessarily reflect the functioning of these communities. In this study, we assess how plant species richness affects the functional composition and diversity of higher trophic levels and discuss how this might affect ecosystem processes, such as herbivory, predation and decomposition. Based on six different consumer traits, we examined the functional composition of arthropod communities sampled in experimental plots that differed in plant species richness. The two components we focused on were functional variation in the consumer community structure (functional structure) and functional diversity, expressed as functional richness, evenness and divergence. We found a consistent positive effect of plant species richness on the functional richness of herbivores, carnivores, and omnivores, but not decomposers, and contrasting patterns for functional evenness and divergence. Increasing plant species richness shifted the omnivore community to more predatory and less mobile species, and the herbivore community to more specialized and smaller species. This was accompanied by a shift towards more species occurring in the vegetation than in the ground layer. Our study shows that plant species richness strongly affects the functional structure and diversity of aboveground arthropod communities. The observed shifts in body size (herbivores), specialization (herbivores), and feeding mode (omnivores) together with changes in the functional diversity may underlie previously observed increases in herbivory and predation in plant communities of higher diversity.

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.

Recent studies have shown that the diversity of flowering plants can enhance pollinator richness and visitation frequency and thereby increase the resilience of pollination. It is assumed that flower traits explain these effects, but it is still unclear which flower traits are responsible, and knowing that, if pollinator richness and visitation frequency are more driven by mass-ratio effects (mean trait values) or by trait diversity. Here, we analyse a three-year data set of pollinator observations collected in a European grassland plant diversity experiment (The Jena experiment). The data entail comprehensive flower trait measurements, including reward traits (nectar and pollen amount), morphological traits (height, symmetry, area, colour spectra) and chemical traits (nectar-amino acid and nectar-sugar concentration). We test if pollinator species richness and visitation frequency of flower communities depend on overall functional diversity combining all flower traits within a community, single trait diversities (within trait variation) and community-weighted means of the single traits, using Bayesian inference. Overall functional diversity did not affect pollinator species richness, but reduced visitation frequency. When looking at individual flower traits separately, we found that single trait diversity of flower reflectance and flower morphology were important predictors of pollinator visitation frequency. Moreover, independent of total flower abundance, community-weighted means of flower height, area, reflectance, nectar-sugar concentration and nectar-amino acid concentration strongly affected both pollinator species richness and visitation frequency. Our results, challenge the idea that functional diversity always positively affects ecosystem functions. Nonetheless, we demonstrate that both single trait diversity and mass-ratio effects of flower traits play an important role for diverse and frequent flower visits, which underlines the functionality of flower traits for pollination services.

Summary 1.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. 2.Here we assessed the role of trait dissimilarities on 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 belowground 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. 3.Community overyielding and the underlying complementarity and competitive dominance varied strongly among the three plant species pools. Overyielding and complementarity was 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. 4.In communities that were assembled based on species variation in only spatial or phenological traits greater competitive dominance was predicted by greater differences 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. 5.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. This article is protected by copyright. All rights reserved.

Plant elemental composition can indicate resource limitation, and changes in key elemental ratios (e.g. plant C:N ratios) can influence rates including herbivory, nutrient recycling, and pathogen infection. Although plant stoichiometry can influence ecosystem-level processes, very few studies have addressed whether and how plant C:N stoichiometry changes with plant diversity and composition. Here, using two long-term experimental manipulations of plant diversity (Jena and Cedar Creek), we test whether plant richness (species and functional groups) or composition (functional group proportions) affects temporal trends and variability of community-wide C:N stoichiometry. Site fertility determined the initial community-scale C:N ratio. Communities growing on N-poor soil (Cedar Creek) began with higher C:N ratios than communities growing on N-rich soil (Jena). However, site-level plant C:N ratios converged through time, most rapidly in high diversity plots. In Jena, plant community C:N ratios increased. This temporal trend was stronger with increasing richness. However, temporal variability of C:N decreased as plant richness increased. In contrast, C:N decreased over time at Cedar Creek, most strongly at high species and functional richness, whereas the temporal variability of C:N increased with both measures of diversity at this site. Thus, temporal trends in the mean and variability of C:N were underlain by concordant changes among sites in functional group proportions. In particular, the convergence of community-scale C:N over time at these very different sites was mainly due to increasing proportions of forbs at both sites, replacing high mean C:N (C4 grasses, Cedar Creek) or low C:N (legumes, Jena) species. Diversity amplified this convergence; although temporal trends differed in sign between the sites, these trends increased in magnitude with increasing species richness. Our results suggest a predictive mechanistic link between trends in plant diversity and functional group composition and trends in the many ecosystem rates that depend on aboveground community C:N. Synthesis We compared the effect of plant diversity on the temporal dynamics of community stoichiometry in two long-term grassland diversity experiments: the Cedar Creek and Jena Experiments. Changes in community C:N ratios were accelerated by increasing diversity at both sites, but in opposite directions depending on soil fertility. Stoichiometry changes were driven by shifts of functional group composition differing in their elemental compositions, the identity of the functional groups depending on the site. Thus, we highlighted that community turnover constrained the effect of diversity on plant stoichiometry at both sites.

Plant diversity is an important driver of nitrogen and phosphorus stocks in aboveground plant biomass of grassland ecosystems, but plant diversity effects on other elements also important for plant growth are less understood. We tested whether plant species richness, functional group richness or the presence/absence of particular plant functional groups influences the Si and Ca concentrations (mmol g(-1)) and stocks (mmol m(-2)) in aboveground plant biomass in a large grassland biodiversity experiment (Jena Experiment). In the experiment including 60 temperate grassland species, plant diversity was manipulated as sown species richness (1, 2, 4, 8, 16) and richness and identity of plant functional groups (1-4; grasses, small herbs, tall herbs, legumes). We found positive species richness effects on Si as well as Ca stocks that were attributable to increased biomass production. The presence of particular functional groups was the most important factor explaining variation in aboveground Si and Ca stocks (mmol m(-2)). Grass presence increased the Si stocks by 140 % and legume presence increased the Ca stock by 230 %. Both the presence of specific plant functional groups and species diversity altered Si and Ca stocks, whereas Si and Ca concentration were affected mostly by the presence of specific plant functional groups. However, we found a negative effect of species diversity on Si and Ca accumulation, by calculating the deviation between mixtures and mixture biomass proportions, but in monoculture concentrations. These changes may in turn affect ecosystem processes such as plant litter decomposition and nutrient cycling in grasslands.

Patterns of feeding interactions between species are thought to influence the stability of communities and the flux of nutrients and energy through ecosystems. However, surprisingly few well-resolved food webs allow us to evaluate factors that influence the architecture of species interactions. We constructed a meta food web consisting of 714 invertebrate species collected over 9 years of suction and pitfall sampling campaigns in the Jena Experiment, a long-term grassland biodiversity experiment located in Jena, Germany. We summarize information on the 51,496 potential trophic links, which were established using information on diet specificity and species traits that typically constrain feeding interactions (trophic group, body size, and vertical stratification). The list of species identities, traits, and link-derivation rules will be useful not only for tests of plant diversity effects on food web structure within the Jena Experiment, but also for considering consistent construction of food webs from empirical data, and for comparisons of network structure across ecosystems. No copyright or proprietary restrictions are associated with the use of this data set other than citation of this Data Paper.

During the last decades, a number of biodiversity experiments have been established to study the effects of plant diversity on ecosystem functioning. This research has been accompanied by a controversial discussion how “diversity effects” in experimental communities are related to the role of biodiversity in “real-world” ecosystems. To explore potential relationships, we compared plant community characteristics of 12 semi-natural managed reference grasslands to selected 10-year old communities of a large grassland biodiversity experiment (Jena Experiment): two communities initially sown with 60 species (JE60), and two communities assembled naturally during succession from bare soil (JESuc). Compared to semi-natural grasslands (17.6 ± 5.6), JE60 had higher species richness (27.5 ± 0.8), while species richness in JESuc (15.2 ± 0.5) was not different on subplots of 0.64 m2 size. Evenness and spatial heterogeneity were similar among grassland types, but biomass proportions of legumes and forbs were higher in JE60, while JESuc and semi-natural grasslands were dominated by grasses. Structural equation modelling applied to identify the drivers of biomass production in mixtures of the Jena Experiment with similar species richness (sown with 8, 16, and 60 species) and reference grasslands, showed no direct relationships between observed species richness and biomass production. In contrast, functional characteristics related to nitrogen acquisition and use were the most important variables explaining community biomass production. These functional characteristics were either driven by management intensity (fertilisation) in the “real world” reference grasslands or established by sowing in the experimental grasslands. Our results imply that species functional characteristics are key for a better understanding of the mechanisms underlying community assembly and ecosystem functioning and that the drivers of ecosystem functioning are not fundamentally different between experimental and “real-world” grasslands. Thus, experimental studies with designed extinction scenarios may help to predict the consequences of species loss for ecosystem functioning in “real-world” ecosystems.

Plant species richness (PSR) increases nutrient uptake which depletes bioavailable nutrient pools in soil. No such relationship between plant uptake and availability in soil was found for phosphorus (P). We explored PSR effects on P mobilisation [phosphatase activity (PA)] in soil. PA increased with PSR. The positive PSR effect was not solely due to an increase in Corg concentrations because PSR remained significant if related to PA:Corg . An increase in PA per unit Corg increases the probability of the temporal and spatial match between substrate, enzyme and microorganism potentially serving as an adaption to competition. Carbon use efficiency of microorganisms (Cmic :Corg ) increased with increasing PSR while enzyme exudation efficiency (PA:Cmic ) remained constant. These findings suggest the need for efficient C rather than P cycling underlying the relationship between PSR and PA. Our results indicate that the coupling between C and P cycling in soil becomes tighter with increasing PSR.

1.) Plants influence associated soil biotic communities that in turn can alter the performance of the subsequently growing plants. Although such “plant–soil feedbacks” (PSFs) are considered as important drivers of plant community assembly, past PSF studies have mainly addressed plant biomass production. However, plant performance is not only the production of biomass but comprises a sequence of different life stages: from seed germination over vegetative growth up to the production of a viable progeny.\ud \ud 2.) Here, we assessed the effects of soil biotic communities that were previously conditioned for 3 years by a focal plant species monoculture or species mixtures on key plant life stages from germination and vegetative growth to flowering and the production of viable seeds. We used three common grassland herb species that were grown in a sterile substrate and inoculated with a sterile control soil or with living soils. Living soils were conditioned either by the focal species in monoculture or a four- or eight-species mixture that included the focal species to represent a decrease in the target plants’ conspecific influence on the soil communities.\ud \ud 3.) We show that the effect of soil biota changed from positive at the plants’ juvenile life stages to neutral or negative at the plants’ adult life stages and ultimately decreased plant fitness. A higher conspecific influence on the soil communities pronounced the positive effects at the juvenile life stage but also the negative effects at adult life stages. Further, we observed direct soil biotic effects on flower production and plant fitness that were not mediated by adult biomass production. This suggests that soil biotic effects may alter plant resource allocation and even may have transgenerational effects on plant fitness.\ud \ud 4.) Synthesis. We conclude that there is no overarching effect of soil biota that remains consistent at all the life stages of a plant. Thus, our results highlight the importance to consider plant life stage and ultimately plant fitness especially when plant–soil interactions are used to explain plant community dynamics.

Contains fulltext : 176862.pdf (Publisher’s version ) (Closed access) 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. 13 p.

In the past two decades, a large number of studies have investigated the relationship between biodiversity and ecosystem functioning, most of which focussed on a limited set of ecosystem variables. The Jena Experiment was set up in 2002 to investigate the effects of plant diversity on element cycling and trophic interactions, using a multi-disciplinary approach. Here, we review the results of 15 years of research in the Jena Experiment, focussing on the effects of manipulating plant species richness and plant functional richness. With more than 85,000 measures taken from the plant diversity plots, the Jena Experiment has allowed answering fundamental questions important for functional biodiversity research.[br/] First, the question was how general the effect of plant species richness is, regarding the many different processes that take place in an ecosystem. About 45% of different types of ecosystem processes measured in the 'main experiment', where plant species richness ranged from 1 to 60 species, were significantly affected by plant species richness, providing strong support for the view that biodiversity is a significant driver of ecosystem functioning. Many measures were not saturating at the 60-species level, but increased linearly with the logarithm of species richness. There was, however, great variability in the strength of response among different processes. One striking pattern was that many processes, in particular belowground processes, took several years to respond to the manipulation of plant species richness, showing that biodiversity experiments have to be long-term, to distinguish trends from transitory patterns. In addition, the results from the Jena Experiment provide further evidence that diversity begets stability, for example stability against invasion of plant species, but unexpectedly some results also suggested the opposite, e.g. when plant communities experience severe perturbations or elevated resource availability. This highlights the need to revisit diversity-stability theory.[br/] Second, we explored whether individual plant species or individual plant functional groups, or biodiversity itself is more important for ecosystem functioning, in particular biomass production. We found strong effects of individual species and plant functional groups on biomass production, yet these effects mostly occurred in addition to, but not instead of, effects of plant species richness.[br/] Third, the Jena Experiment assessed the effect of diversity on multitrophic interactions. The diversity of most organisms responded positively to increases in plant species richness, and the effect was stronger for above-than for belowground organisms, and stronger for herbivores than for carnivores or detritivores. Thus, diversity begets diversity. In addition, the effect on organismic diversity was stronger than the effect on species abundances.[br/] Fourth, the Jena Experiment aimed to assess the effect of diversity on N, P and C cycling and the water balance of the plots, separating between element input into the ecosystem, element turnover, element stocks, and output from the ecosystem. While inputs were generally less affected by plant species richness, measures of element stocks, turnover and output were often positively affected by plant diversity, e.g. carbon storage strongly increased with increasing plant species richness. Variables of the N cycle responded less strongly to plant species richness than variables of the C cycle.[br/] Fifth, plant traits are often used to unravel mechanisms underlying the biodiversity-ecosystem functioning relationship. In the Jena Experiment, most investigated plant traits, both above-and belowground, were plastic and trait expression depended on plant diversity in a complex way, suggesting limitation to using database traits for linking plant traits to particular functions.[br/] Sixth, plant diversity effects on ecosystem processes are often caused by plant diversity effects on species interactions. Analyses in the Jena Experiment including structural equation modelling suggest complex interactions that changed with diversity, e.g. soil carbon storage and greenhouse gas emission were affected by changes in the composition and activity of the belowground microbial community. Manipulation experiments, in which particular organisms, e.g. belowground invertebrates, were excluded from plots in split-plot experiments, supported the important role of the biotic component for element and water fluxes.[br/] Seventh, the Jena Experiment aimed to put the results into the context of agricultural practices in managed grasslands. The effect of increasing plant species richness from 1 to 16 species on plant biomass was, in absolute terms, as strong as the effect of a more intensive grassland management, using fertiliser and increasing mowing frequency. Potential bioenergy production from high-diversity plots was similar to that of conventionally used energy crops. These results suggest that diverse 'High Nature Value Grasslands' are multifunctional and can deliver a range of ecosystem services including production-related services.[br/] A final task was to assess the importance of potential artefacts in biodiversity-ecosystem functioning relationships, caused by the weeding of the plant community to maintain plant species composition. While the effort ( in hours) needed to weed a plot was often negatively related to plant species richness, species richness still affected the majority of ecosystem variables. Weeding also did not negatively affect monoculture performance; rather, monocultures deteriorated over time for a number of biological reasons, as shown in plant-soil feedback experiments.[br/] To summarize, the Jena Experiment has allowed for a comprehensive analysis of the functional role of biodiversity in an ecosystem. A main challenge for future biodiversity research is to increase our mechanistic understanding of why the magnitude of biodiversity effects differs among processes and contexts. It is likely that there will be no simple answer. For example, among the multitude of mechanisms suggested to underlie the positive plant species richness effect on biomass, some have received limited support in the Jena Experiment, such as vertical root niche partitioning. However, others could not be rejected in targeted analyses. Thus, from the current results in the Jena Experiment, it seems likely that the positive biodiversity effect results from several mechanisms acting simultaneously in more diverse communities, such as reduced pathogen attack, the presence of more plant growth promoting organisms, less seed limitation, and increased trait differences leading to complementarity in resource uptake. Distinguishing between different mechanisms requires careful testing of competing hypotheses. Biodiversity research has matured such that predictive approaches testing particular mechanisms are now possible.

Plant functional characteristics may drive plant species richness effects on ecosystem processes. Consequently, the focus of biodiversity–ecosystem functioning (BEF) experiments has expanded from the manipulation of plant species richness to manipulating functional trait composition. Involving ecophysiological plant traits in the experimental design might allow for a better understanding of how species loss alters ecosystem processes. Here we provide the theoretical background, design and first results of the ‘Trait-Based Biodiversity Experiment’ (TBE), established in 2010 that directly manipulates the trait composition of experimental plant communities. Analysis of six plant traits related to resource acquisition and use were analyzed using principal component analysis of 60 grassland species. The resulting two main axes describe gradients in functional similarity, and were used as the basis for designing plant communities with different functional and species diversity levels. Using such an approach allowed us to manipulate different levels of complementarity in spatial and temporal plant resource acquisition. In contrast to previous biodiversity experiments, the TBE is designed according to more realistic scenarios of non-random species loss along orthogonal axes of species trait dissimilarities. This allows us to tease apart the relative importance of selection and complementarity effects on multiple ecosystem processes, and to mechanistically study the consequences of plant community simplification.

Plant diversity is a key driver of ecosystem functioning best documented for its influence on plant productivity. The strength and direction of plant diversity effects on species interactions across trophic levels are less clear. For example, with respect to the interactions between herbivorous invertebrates and plants, a number of competing hypotheses have been proposed that predict either increasing or decreasing community herbivory with increasing plant species richness. We investigated foliar herbivory rates and consumed leaf biomass along an experimental grassland plant diversity gradient in year eight after establishment. The gradient ranged from one to 60 plant species and manipulated also functional group richness (from one to four functional groups-legumes, grasses, small herbs, and tall herbs) and plant community composition. Measurements in monocultures of each plant species showed that functional groups differed in the quantity and quality of herbivory damage they experienced, with legumes being more damaged than grasses or non-legume herbs. In mixed plant communities, herbivory increased with plant diversity and the presence of two key plant functional groups in mixtures had a positive (legumes) and a negative (grasses) effect on levels of herbivory. Further, plant community biomass had a strong positive impact on consumed leaf biomass, but little effect on herbivory rates. Our results contribute detailed data from a well-established biodiversity experiment to a growing body of evidence suggesting that an increase of herbivory with increasing plant diversity is the rule rather than an exception. Considering documented effects of herbivory on other ecosystem functions and the increase of herbivory with plant diversity, levels of herbivory damage might not only be a result, but also a trigger within the diversity-productivity relationship.

In many environments land use intensification is likely to result in a decrease in species richness and in an increase in eutrophication. Although the importance of both factors for higher trophic levels such as insect herbivores is well documented, their impact has rarely been studied in combination. Herbivorous insects have a strong impact on the functioning of ecosystems and it is therefore important to understand how they are affected by eutrophication in high or low diversity environments. We used a grassland biodiversity experiment to investigate the combined effect of fertilization and plant diversity loss on the fitness of the generalist grasshopper Chorthippus parallelus by rearing grasshopper nymphs for four weeks in cages on unfertilized or fertilized (NPK) subplots across a species richness gradient from 1 to 60 plant species. Survival, the number of oothecae, body mass and the number of hatchlings were measured separately for each cage. Plant diversity had no effect on any of the grasshopper fitness measures, neither in unfertilized nor in fertilized plots. NPK-fertilization reduced grasshopper survival but increased body mass of males and reproductive success of the surviving females. Fertilization effects were not mediated by plant community structure, productivity or composition, suggesting that higher food plant quality was one of the main drivers. There was no interaction between plant diversity and fertilization on any of the measures. In conclusion, an increase in eutrophication, in both species-rich and species-poor grasslands, could lead to higher reproductive success and therefore higher abundances of herbivorous insects including insect pests, with fertilization effects dominating plant diversity effects.

Ongoing biodiversity decline impairs ecosystem processes, including pollination. Flower visitation, an important indicator of pollination services, is influenced by plant species richness. However, the spatio-temporal responses of different pollinator groups to plant species richness have not yet been analyzed experimentally. Here, we used an experimental plant species richness gradient to analyze plant-pollinator interactions with an unprecedented spatio-temporal resolution. We observed four pollinator functional groups (honeybees, bumblebees, solitary bees, and hoverflies) in experimental plots at three different vegetation strata between sunrise and sunset. Visits were modified by plant species richness interacting with time and space. Furthermore, the complementarity of pollinator functional groups in space and time was stronger in species-rich mixtures. We conclude that high plant diversity should ensure stable pollination services, mediated via spatio-temporal niche complementarity in flower visitation. Declining plant diversity has been shown to affect ecosystem processes such as plant-pollinator interactions, but it is currently not known if or how spatio-temporal niche partitioning of pollinators is affected by plant biodiversity. In a grassland biodiversity experiment, where we manipulated plant species richness and studied spatio-temporal resource use of pollinators, we found that complementarity of pollinator groups in space and time was stronger in species-rich mixtures. Our study shows that high plant diversity may ensure stable pollination services due to increased pollinator complementarity.

Pollinators play a key role in the reproduction of most plant species, and pollinator and plant diversity are often related. We studied an experimental gradient of plant species richness for a better understanding of plantpollinator community interactions and their temporal variability, because in non-experimental field surveys plant richness is often confounded with gradients in management, soil fertility, and community composition. We observed pollinator species richness and frequency of visits six times in 73 plots over two years, and used advanced statistical analysis to account for the high number of zeroes that often occur in count data of rare species. The frequency of pollinator visits increased linearly with both the blossom cover and the number of flowering plant species, which was closely related to the total number of plant species, whereas the number of pollinator species followed a saturation curve. The presence of particularly attractive plant species was only important for the frequency of flower visits, but not to the richness of pollinators. Plant species richness, blossom cover, and the presence of attractive plant species enhanced the temporal stability in the frequency of pollinator visits. In conclusion, grasslands with high plant diversity enhance and stabilize frequent and diverse flower visitations, which should sustain effective pollination and plant reproduction.

Die Artenvielfalt von Pflanzen strukturiert die Gesellschaften höherer trophischer Ebenen und verbessert die Fortpflanzung und Fitness von Pflanzen-assoziierten Insekten. Dieser Einfluss auf höhere trophische Ebenen kann von der Quantität (Verfügbarkeit) und Qualität (Zusammensetzung) der Ressourcen abhängen. Wir untersuchten die Stöchiometrie von Interaktionen zwischen Pflanzen und zwei funktionellen Insektengruppen (Herbivoren, Bestäuber) entlang des experimentellen Pflanzendiversitätsgradienten im „Jena-Experiment“. Wir analysierten den prozentuellen Anteil von Kohlenstoff (C), Stickstoff (N) und Phosphat (P), sowie die entsprechenden molaren Verhältnisse dieser Elemente (C:N, C:P, N:P) bei einer bestäubenden Bienenart (Chelostoma distinctum) und einer herbivoren Heuschreckenart (Chorthippus parallelus), welche wir auf Graslandflächen verschiedener Diversitätsstufen gezüchtet haben. Insekten zeigten höhere prozentuale Anteile in der Trockenmasse (C, N und P) und niedrigere C:N- und C:P-Verhältnisse als Pflanzen. Das C:N-Verhältnis war bei Heuschrecken signifikant höher als bei den Bienen, und in beiden Gruppen bei den Weibchen höher als bei den Männchen. Zunehmende Pflanzenvielfalt erhöhte das C:N-Verhältnis von männlichen Bienen und weiblichen Heuschrecken und die Insektenstöchiometrie beider Gruppen hängte positiv mit der Pflanzenstöchiometrie zusammen (männliche Bienen: C:P und N:P; Heuschrecken: C:N und N:P). Unsere Studie zeigt unterschiedliche Stöchiometrie von antagonistischen und mutualistischen Interaktionen. Daraus ergeben sich verschiedene Schlussfolgerungen für diversitätsgetriebene Veränderungen von der Elementzusammensetzung bei Pflanzen verschiedener trophischer und funktioneller Gruppen. Changes in plant diversity have consequences for higher trophic levels, e.g., higher plant diversity can enhance the reproduction and fitness of plant-associated insects. This response of higher trophic levels potentially depends on diversity-related changes in both resource quantity (abundance) and quality (nutritional content). The availability of elemental nutrients in plant resources is one aspect of nutritional quality, but has rarely been addressed as a pathway relating plant diversity to associated insects. Using the experimental plant diversity gradient of a large biodiversity grassland project, the Jena-Experiment, we analysed the %C, %N and %P and the molar ratios of those elements (C:N, C:P and N:P) in a pollinating bee, Chelostoma distinctum, and an herbivorous grasshopper, Chorthippus parallelus, reared on plots of different plant diversity. Insects showed higher content of C, N and P (% dry mass), and lower C:N and C:P ratios than plants. C:N ratios were significantly higher in grasshoppers than in bees and higher in females than in males of both species. Increasing plant species richness increased the C:N ratio of male bees and female grasshoppers. In both groups, stoichiometry was positively related to plant stoichiometry (male bees: C:P and N:P; grasshoppers: C:N and N:P). Path analysis revealed that diversity-driven changes in plant elemental composition can have consequences for abundance and chemical composition of higher trophic levels, with different responses of the two functional groups.

Biodiversity experiments generally report a positive effect of plant biodiversity on aboveground biomass (overyielding), which typically increases with time. Various studies also found overyielding for belowground plant biomass, but this has never been measured over time. Also, potential underlying mechanisms have remained unclear. Differentiation in rooting patterns among plant species and plant functional groups has been proposed as a main driver of the observed biodiversity effect on belowground biomass, leading to more efficient belowground resource use with increasing diversity, but so far there is little evidence to support this. We analyzed standing root biomass and its distribution over the soil profile, along a 1-16 species richness gradient over eight years in the Jena Experiment in Germany, and compared belowground to aboveground overyielding. In our long-term dataset, total root biomass increased with increasing species richness but this effect was only apparent after four years. The increasingly positive relationship between species richness and root biomass, explaining 12% of overall variation and up to 28% in the last year of our study, was mainly due to decreasing root biomass at low diversity over time. Functional group composition strongly affected total standing root biomass, explaining 44% of variation, with grasses and legumes having strong overall positive and negative effects, respectively. Functional group richness or interactions between functional group presences did not strongly contribute to overyielding. We found no support for the hypothesis that vertical root differentiation increases with species richness, with functional group richness or composition. Other explanations, such as stronger negative plant-soil feedbacks in low-diverse plant communities on standing root biomass and vertical distribution should be considered.

In order to predict which ecosystem functionsare most at risk from biodiversity loss, meta-analyses havegeneralised results from biodiversity experiments overdifferent sites and ecosystem types. In contrast, comparingthe strength of biodiversity effects across a large number ofecosystem processes measured in a single experimentpermits more direct comparisons. Here, we present ananalysis of 418 separate measures of 38 ecosystem processes.Overall, 45 % of processes were significantlyaffected by plant species richness, suggesting that, whilediversity affects a large number of processes not allrespond to biodiversity. We therefore compared thestrength of plant diversity effects between different categoriesof ecosystem processes, grouping processesaccording to the year of measurement, their biogeochemicalcycle, trophic level and compartment (above- orbelowground) and according to whether they were measuresof biodiversity or other ecosystem processes, biotic orabiotic and static or dynamic. Overall, and for severalindividual processes, we found that biodiversity effectsbecame stronger over time. Measures of the carbon cyclewere also affected more strongly by plant species richnessthan were the measures associated with the nitrogen cycle. In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45 % of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination.

Agricultural intensification is a major driver of global environmental change. Disentangling the relative impact of losses in plant species richness and intensified management on higher trophic level organisms is important for conservation recommendations.We established different management regimes along an experimental gradient of plant species richness within “The Jena-Experiment” in Germany and quantified herbivory as well as grasshoppers and pollinators. Herbivory, grasshopper density and species richness and frequency of flower visiting pollinators were recorded two times in each of four subplots of altogether 80 plots differing in plant species richness. Each of the four subplots was subject to four different levels of fertilizer application and mowing to simulate very low, low, high and very high land use intensity.Fertilization and mowing significantly affected plant–herbivore interactions but plant species richness had no discernible effect. Grasshoppers were most abundant at high intensity subplots (3.1 individuals per m2) and least abundant on very low intensity subplots (1.3 individuals per m2). Leaf damage caused by herbivores was highest in even the very high intensity subplots (3.7%) with four mowing events per year and high amounts of fertilizer application and lowest on subplots with a low management intensity (2.4%) comprising two mowing events per year but no fertilizer application. In contrast, pollinators benefited most from lower management intensities, with only one or two mowing events and no fertilizer addition. In addition, higher numbers of flowering plant species and increased blossom cover was associated with enhanced pollinator species richness and flower visitation.Our results indicate that even in grasslands with high plant species richness, mowing and fertilization are more important drivers of herbivory and flower visitation by pollinators. Management with no more than two cuts per year and without fertilizer application in our grasslands balanced the ecosystem functions of increased pollination and decreased herbivory.

Plant diversity changes can impact the abundance, diversity, and functioning of species at higher trophic levels. We used an experimental gradient in grassland plant diversity ranging from 1 to 16 plant species to study multitrophic interactions among plants, cavity-nesting bees and wasps, and their natural enemies, and analysed brood cell density, insect diversity (species richness), and bee and wasp community similarity over two consecutive years. The bee and wasp communities were more similar among the high (16 species) diversity plots than among plots of the lower diversity levels (up to 8 species), and a more similar community of bees and wasps resulted in a more similar community of their parasitoids. Plant diversity, which was closely related to flower diversity, positively and indirectly affected bee diversity and the diversity of their parasitoids via increasing brood cell density of bees. Increasing plant diversity directly led to higher wasp diversity. Parasitism rates of bees and wasps (hosts) were not affected by plant diversity, but increased with the diversity of their respective parasitoids. Decreases in parasitism rates of bees arose from increasing brood cell density of bees (hosts), whereas decreasing parasitism rates of wasps arose from increasing wasp diversity (hosts). In conclusion, decreases in plant diversity propagated through different trophic levels: from plants to insect hosts to their parasitoids, decreasing density and diversity. The positive relationship between plant diversity and the community similarity of higher trophic levels indicates a community-stabilising effect of high plant diversity. Plant diversity changes can impact the abundance,diversity, and functioning of species at higher trophiclevels. We used an experimental gradient in grasslandplant diversity ranging from 1 to 16 plant species to studymultitrophic interactions among plants, cavity-nesting beesand wasps, and their natural enemies, and analysed broodcell density, insect diversity (species richness), and bee andwasp community similarity over two consecutive years.The bee and wasp communities were more similar amongthe high (16 species) diversity plots than among plots of thelower diversity levels (up to 8 species), and a more similarcommunity of bees and wasps resulted in a more similarcommunity of their parasitoids. Plant diversity, which wasclosely related to flower diversity, positively and indirectlyaffected bee diversity and the diversity of their parasitoidsvia increasing brood cell density of bees. Increasing plantdiversity directly led to higher wasp diversity. Parasitismrates of bees and wasps (hosts) were not affected by plantdiversity, but increased with the diversity of their respectiveparasitoids. Decreases in parasitism rates of bees arosefrom increasing brood cell density of bees (hosts), whereasdecreasing parasitism rates of wasps arose from increasingwasp diversity (hosts). In conclusion, decreases in plantdiversity propagated through different trophic levels: fromplants to insect hosts to their parasitoids, decreasing densityand diversity. The positive relationship between plantdiversity and the community similarity of higher trophiclevels indicates a community-stabilising effect of highplant diversity.

Although most plants benefit from pollen vectors, very little information exists about how plant diversity structures the interactions between plants and their flower visitors. The structure of such interaction webs holds information about specialization and effectiveness of flower visitors in flower resource use. Here, we analyzed 52 plant–flower visitor interaction webs along a gradient of experimentally manipulated plant species richness in a European grassland. The gradient allows testing for effects of the number of flowering plant species per se. Linkage density and interaction diversity between flowering plant species and their visiting insect species increased with higher richness of flowering species. Increased interaction diversity led to smaller temporal variability in the frequency of flower visits. These results suggest higher temporal stability of pollination provided for plants integrated in complex interaction webs with a high number of flowering plant species. Die meisten Pflanzen werden durch Pollenüberträger begünstigt, jedoch ist wenig bekannt über die Auswirkungen von Pflanzendiversität auf die Interaktionen zwischen Pflanzen und ihren Blütenbesuchern. Die Struktur dieser Interaktionsnetze liefert wichtige Informationen über Spezialisierung und Effektivität der Blütenbesucher in ihrer Resourcennutzung. Wir untersuchten 52 Pflanze–Blütenbesucher-Interaktionsnetze eines europäischen Graslandes entlang eines experimentellen Gradienten in der Anzahl von Pflanzenarten. Der experimentelle Gradient bietet uns die Möglichkeit den Einfluss der Anzahl der blühenden Pflanzenarten per se zu untersuchen. Linkdichte (linkage density) und Interaktionsdiversität (interaction diversity) zwischen den blühenden Pflanzenarten und ihren Blütenbesuchern nahmen mit der Anzahl der blühenden Pflanzenarten zu. Ein Anstieg in der Interaktionsdiversität führte wiederum zu einer Abnahme in der zeitlichen Variabilität. Die Ergebnisse lassen auf höhere zeitliche Stabilität in der Bestäubung von Pflanzen schließen, die von einer hohen Anzahl an blühenden Pflanzenarten umgeben sind und somit in ein komplexes Interaktionsnetz integriert sind. Die Spezialisierung auf Blütenresourcen nahm bei den solitären Bienen mit zunehmender Anzahl an blühenden Pflanzenarten zu, nicht jedoch bei Honigbienen und Hummeln. Der Schutz von diversen Graslandflächen führt demnach zu höherer Resourcenspezialiserung, und kann somit eventuell eine Zunahme in der Bestäubungsleistung fördern.

Aims Invasion resistance in experimental plant communities is known to increase with increasing diversity and further to depend on the presence of particular functional groups. To test whether these effects also hold true for the invader establishment phase beyond the seedling stage, we studied survival and performance of Centaurea jacea L. (brown knapweecl) planted into experimental grassland communities of varying plant biodiversity over three consecutive years. Moreover, we analysed the role of insect herbivory and biomass of the recipient community for mediating diversity effects. Methods In 2005, seedlings of Centaurea were transplanted into experimental grassland communities (the Jena Experiment) covering a species richness (1-60) and functional group richness (1-4) gradient. Half of these transplants and the community surrounding them in each plot were sprayed with insecticide while the other half served as control. In 2006 and 2007 (during the second and third year after transplantation), we recorded survival, growth-related (e.g. transplant biomass, height) and reproduction-related traits (e.g. number of flower heads). Annual data on community aboveground biomass served as covariate to investigate mediating effects of aboveground competition with the recipient community. Important Findings Species richness was the most important factor responsible for Centaurea limitation. Higher levels of diversity decreased survival and all performance traits in both years. These diversity effects were partly driven by community biomass, but not fully explained by that covariate, suggesting the importance also of further processes. The influence of functional group richness was strong in the second year after transplantation and weaker in the third year. Among the particular functional groups, only the presence of legumes showed strong negative effects on Centaurea survival and weak negative effects on growth and reproduction, the latter two being mediated by biomass. Insect herbivore reduction considerably benefited Centaurea in sprayed monocultures, where it grew significantly larger than in all other diversity levels and than in the control subplots. We conclude that effects of plant community properties on invading individuals change in the course of establishment, that plant species richness effects are also important during later stages of establishment, and that biomass (especially at high diversity) and herbivory (especially at low diversity) of the recipient community are important in mediating community effects on invaders.