At eight European field sites, the impact of loss of plant diversity on primary productivity was simulated by synthesizing grassland communities with different numbers of plant species. Results differed in detail at each location, but there was an overall log-linear reduction of average aboveground biomass with loss of species. For a given number of species, communities with fewer functional groups were less productive. These diversity effects occurred along with differences associated with species composition and geographic location. Niche complementarity and positive species interactions appear to play a role in generating diversity-productivity relationships within sites in addition to sampling from the species pool.

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects.We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives. Geosphere-Biosphere Program (IGBP) and DIVERSITAS, the TRY database (TRY-not an acronym, rather a statement of sentiment; https ://www.try-db.org; Kattge et al., 2011) was proposed with the explicit assignment to improve the availability and accessibility of plant trait data for ecology and earth system sciences. The Max Planck Institute for Biogeochemistry (MPI-BGC) offered to host the database and the different groups joined forces for this community-driven program. Two factors were key to the success of TRY: the support and trust of leaders in the field of functional plant ecology submitting large databases and the long-term funding by the Max Planck Society, the MPI-BGC and the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, which has enabled the continuous development of the TRY database.

Abstract. Insurance effects of biodiversity can stabilize the functioning of multispecies ecosystems against environmental variability when differential species' responses lead to asynchronous population dynamics. When responses are not perfectly positively correlated, declines in some populations are compensated by increases in others, smoothing variability in ecosystem productivity. This variance reduction effect of biodiversity is analogous to the riskspreading benefits of diverse investment portfolios in financial markets.We use data from the BIODEPTH network of grassland biodiversity experiments to perform a general test for stabilizing effects of plant diversity on the temporal variability of individual species, functional groups, and aggregate communities. We tested three potential mechanisms: reduction of temporal variability through population asynchrony; enhancement of long-term average performance through positive selection effects; and increases in the temporal mean due to overyielding.Our results support a stabilizing effect of diversity on the temporal variability of grassland aboveground annual net primary production through two mechanisms. Two-species communities with greater population asynchrony were more stable in their average production over time due to compensatory fluctuations. Overyielding also stabilized productivity by increasing levels of average biomass production relative to temporal variability. However, there was no evidence for a performance-enhancing effect on the temporal mean through positive selection effects. In combination with previous work, our results suggest that stabilizing effects of diversity on community productivity through population asynchrony and overyielding appear to be general in grassland ecosystems.

Ecosystem effects of biodiversity manipulations in European grasslands AbstractWe present a multisite analysis of the relationship between plant diversity and ecosystem functioning within the European BIODEPTH network of plant-diversity manipulation experiments. We report results of the analysis of 11 variables addressing several aspects of key ecosystem processes like biomass production, resource use (space, light, and nitrogen), and decomposition, measured across three years in plots of varying plant species richness at eight different European grassland field sites. Differences among sites explained substantial and significant amounts of the variation of most of the ecosystem processes examined. However, against this background of geographic variation, all the aspects of plant diversity and composition we examined (i.e., both numbers and types of species and functional groups) produced significant, mostly positive impacts on ecosystem processes.Analyses using the additive partitioning method revealed that complementarity effects (greater net yields than predicted from monocultures due to resource partitioning, positive interactions, etc.) were stronger and more consistent than selection effects (the covariance between monoculture yield and change in yield in mixtures) caused by dominance of species with particular traits. In general, communities with a higher diversity of species and functional groups were more productive and utilized resources more completely by intercepting more light, taking up more nitrogen, and occupying more of the available space. Diversity had significant effects through both increased vegetation cover and greater nitrogen retention by plants when this resource was more abundant through N2 fixation by legumes. However, additional positive diversity effects remained even after controlling for differences in vegetation cover and for the presence of legumes in communities. Diversity effects were stronger on above-than belowground processes. In particular, clear diversity effects on decomposition were only observed at one of the eight sites.The ecosystem effects of plant diversity also varied between sites and years. In general, diversity effects were lowest in the first year and stronger later in the experiment, indicating that they were not transitional due to community establishment. These analyses of our complete ecosystem process data set largely reinforce our previous results, and those from comparable biodiversity experiments, and extend the generality of diversity-ecosystem functioning relationships to multiple sites, years, and processes. Abstract. We present a multisite analysis of the relationship between plant diversity and ecosystem functioning within the European BIODEPTH network of plant-diversity manipulation experiments. We report results of the analysis of 11 variables addressing several aspects of key ecosystem processes like biomass production, resource use (space, light, and nitrogen), and decomposition, measured across three years in plots of varying plant species ri...

Geographic variation can lead to the evolution of different local varieties, even in widespread forage plants. We investigated the performance of common forage plants in relation to their genetic diversity and local adaptation at a continental scale using reciprocal transplants at eight field sites across Europe over a 2‐year period. The overall performance of the three test species, Trifolium pratense, Dactylis glomerata, Plantago lanceolata, was generally highest for plants replanted at their home site and declined with increasing transplanting distance. The three species differed in the fitness components responsible for the increased overall performance and selection advantage at home sites. In addition to the effects of local adaptation, the majority of measured traits in all three species also showed ecotypic variation. However, no single ecotype of any species was able to outperform the locally adapted strains and do best at all sites, highlighting the importance of maintaining these plant genetic resources.

To investigate how plant diversity loss affects nitrogen accumulation in above‐ground plant biomass and how consistent patterns are across sites of different climatic and soil conditions, we varied the number of plant species and functional groups (grasses, herbs and legumes) in experimental grassland communities across seven European experimental sites (Switzerland, Germany, Ireland, United Kingdom (Silwood Park), Portugal, Sweden and Greece). Nitrogen pools were significantly affected by both plant diversity and community composition. Two years after sowing, nitrogen pools in Germany and Switzerland strongly increased in the presence of legumes. Legume effects on nitrogen pools were less pronounced at the Swedish, Irish and Portuguese site. In Greece and UK there were no legume effects. Nitrogen concentration in total above‐ground biomass was quite invariable at 1.66±0.03% across all sites and diversity treatments. Thus, the presence of legumes had a positive effect on nitrogen pools by significantly increasing above‐ground biomass, i.e. by increases in vegetation quantity rather than quality. At the German site with the strongest legume effect on nitrogen pools and biomass, nitrogen that was fixed symbiotically by legumes was transferred to the other plant functional groups (grasses and herbs) but varied depending on the particular legume species fixing N and the non‐legume species taking it up. Nitrogen‐fixation by legumes therefore appeared to be one of the major functional traits of species that influenced nitrogen accumulation and biomass production, although effects varied among sites and legume species. This study demonstrates that the consequences of species loss on the nitrogen budget of plant communities may be more severe if legume species are lost. However, our data indicate that legume species differ in their N2 fixation. Therefore, loss of an efficient N2‐fixer (Trifolium in our study) may have a greater influence on the ecosystem function than loss of a less efficient species (Lotus in our study). Furthermore, there is indication that P availability in the soil facilitates the legume effect on biomass production and biomass nitrogen accumulation.

Understanding the influence of environmental variation on the relationship between biodiversity and ecosystem functioning is of theoretical and practical interest. We predicted that the strength of this relationship should increase with available biotope space (the physical space associated with a speciesÕ niche) due to increased niche complementarity between species. In this study, biotope space specifically refers to soil volume which is associated with the niche dimension of nutrient acquisition. We tested our prediction by growing plant communities on a gradient of increasing soil depth and volume, offering increased rooting space to species. Our results provide support for a linear increase of the magnitude of positive biodiversity effects on above-and belowground community biomass with increasing biotope space. This increase was caused by complementarity effects between species. Soil erosion may thus reduce intercropping benefits.

Understanding the relative importance of the abiotic environment and species interactions in determining the distribution and abundance of organisms has been a challenge in ecological research. Serpentine substrata are stressful environments for plant growth due to multiple limitations, collectively called the "serpentine syndrome". In the present review, our aim is not only to describe recent work in serpentine ecology, but also to highlight specific mechanisms of species tolerance and adaptation to serpentine soils and their effects on community structure and ecosystem functioning. We present hypotheses of the development of serpentine endemism and a description of functional traits of serpentine plants together with a synthesis of species interactions in serpentine soils and their effects on community structure and ecosystem productivity. In addition, we propose hypotheses about the effects of the 'serpentine syndrome' on ecosystem processes including productivity and decomposition.