Das Projekt "Controls of plant biodiversity on water flux partitioning in grassland ecosystems" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Institut für Agrarwissenschaften, Departement Biologie durchgeführt. Global environmental change is predicted to result in increased frequency and intensity of extreme climatic events, including severe droughts and intense precipitation events (IPCC, 2001; IPCC, 2007). The determination and partitioning of water use of entire ecosystems will thus gain increasing importance under future climatic conditions (IPCC 2007). Studying the effects of plant diversity on ecosystem water fluxes is also a crucial aspect of our understanding of the mechanisms underlying the response of ecosystems to global change as well as the direction and magnitude of potential feedback effects of ecosystems on the hydrological cycle and the atmosphere. However, up to now, biodiversity-ecosystem functioning studies have neglected the water cycle almost completely. In the proposed project, the controls of plant diversity (i.e., species richness and functional group richness) on ecosystem water fluxes, their partitioning into soil evaporation and transpiration as well as plant water uptake patterns will be assessed in grassland ecosystems with the following objectives: - To quantify water losses from grassland ecosystems of varying plant diversity to the atmosphere (evapotranspiration fluxes); - To partition the evapotranspiration flux into its soil evaporative and vegetation transpiration components; - to identify the environmental constraints of plant water sources as a function of plant diversity. The study will be carried out at The Jena Experiment, a large biodiversity experiment in which experimental plant community plots of varying species composition, but also species and functional group richness are studied since 2002. We propose to use micrometeorological techniques to measure the ecosystem evapotranspiration flux (ET) and partition it into vegetation transpiration (T) and soil evaporation (E) at the ecosystem level, as well as to use stable isotope analyses to identify the source water of transpiration during intensive field campaigns at times of different water availability. The expected outcomes of the project proposed are manyfold. Using an innovative combination of techniques, we can provide a proof-of-concept to a scientific community (e.g. biodiversity, population biology, plant ecology communities) that typically has little to no knowledge about the great potential of such methodology. We will obtain highly relevant data on the relationships between plant diversity and water fluxes, their component fluxes and environmental drivers, information that does not exist at the moment. Moreover, we then can assess land surface-atmosphere coupling and the impact of climate change on grassland ecosystems, one of the major land use types in Europe and globally.