Effects of disturbance, seed addition and land-use intensity on plant community assembly and ecosystem functions in grasslands (ESCAPE II)

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The proposed project ESCAPE II focuses on plant community (re-)assembly in relation to a range of different ecosystem functions, land-use intensity and plant diversity. A special emphasis is given to the resilience of these functions and relationships after disturbance and to effects of experimentally increased plant diversity on both. Therefore, we will continue the monitoring of the newly established seed addition and disturbance experiment SADE in combination with complementing analyses on all 150 Experimental Plots and on experimental plant communities (mesocosms). During the current phase and in close cooperation with the Botany core project, we successfully installed this large-scale experiment, which will now serve as a unique experimental platform for joint research on the functional role of biodiversity within the grasslands of Biodiversity Exploratories. First results already showed significantly higher plant diversity in seeded plots after disturbance indicating that these treatments were successful in overcoming dispersal and microsite limitation. Our preliminary work also revealed pronounced effects of plant diversity on ecosystem functioning; e.g. isotopic abundances of 13C and 15N in plant biomass indicated reduced sensitivity towards drought and more complete nutrient use at higher levels of plant diversity on EP level. Further, we found increased downwards relocation of N on soils of disturbed SADE plots, especially under high fertilization intensity. In a small-scale sod experiment, N losses also increased due to the interaction of fertilization and drought stress. This increase was in turn moderated by higher plant diversity. During the next phase, we will use and maintain the SADE experiment, where the increase in plant diversity now becomes increasingly available, to mechanistically assess the functional role of plant diversity on a wide range of ecosystem processes. In detail, we will monitor vegetation trajectories, assess effects of seed rain, analyse 13C and 15N isotopic abundances in and the quantity and quality of plant biomass, quantify nutrient retention and litter decomposition. In a complementary mesocosm experiment, we will specifically address the mechanism of nutrient partitioning among plant species in interdependency with plant diversity, fertilization intensity and climate (drought).Our main hypotheses are that i) plant diversity has a positive effect on different ecosystem functions and their resilience after disturbance; ii) land-use intensity and/or its single components have strong direct and indirect effects on these functions (mediated by plant diversity); iii) community (re-) assembly and the recovery of ecosystem functions after disturbance depends on the functional richness of the local seed rain. As in the current phase, we will take over the coordination of activities on the SADE plots and will encourage collaboration and synthesis.