Selection shapes plant performance in a grassland biodiversity experiment

O_LIThe increasing strength of positive biodiversity effects on plant community productivity in long-term biodiversity experiments has been shown to be related to mixed responses at species level. However, it is still not well understood if the varying environments in plant communities with different diversity also exert different selection pressures to which plant species respond adaptively or whether their responses are mainly due to phenotypic plasticity. C_LIO_LIWe conducted a transplant experiment for nine plant species in a 17-year-old grassland biodiversity experiment (Jena Experiment). We used offspring of plants selected in communities with different diversity or from plants which did not experience selection in the experiment (naive). In a Community History Experiment, offspring of selected plants were planted in three test environments: their original plant communities with original soil, newly assembled plant communities with original soil, and newly assembled plant communities with new soil. Additionally, in a Selection Experiment we compared the performance of selected plants grown in their original environment to the performance of naive plants grown in the same environment. C_LIO_LIIn all test environments, increasing species richness was on average associated with a decrease in plant individual biomass, reproductive output, relative growth rate, plant height, leaf greenness, and leaf nitrogen (N) concentration and an increase in SLA. C_LIO_LIIn the Community History Experiment survival was lower, while plant height, SLA, leaf N and C concentrations were highest in the test environment without plant and soil history. In high-diversity communities, individuals produced more biomass, grew taller and had higher leaf greenness in the original environment than in the other test environments. C_LIO_LIIn the Selection Experiment selected plants had weaker decline in their biomass, taller stature, and higher leaf C and N concentrations than C_LIO_LInaive plants with increasing species richness. C_LIO_LIIn both experiments, we found evidences of adaptive phenotypic responses. Specifically, in high-diversity communities, selected plants showed higher performance in their original environment, largely explained by plant community history and positive plant-soil feedbacks established over time. C_LIO_LISynthesis: Our study highlights the important role of eco-evolutionary feedbacks of species diversity, which affect plant performance over time. C_LI