Das Projekt "Microbial control of ecosystem functioning" wird vom Umweltbundesamt gefördert und von Forschungsanstalt Agroscope Reckenholz-Tänikon ART durchgeführt. Nutrient loss from ecosystems has become of global major global concern as it reduces the sustainability of ecosystems and because it causes eutrophication of surface water. In this project we investigate whether soil fungi enhance ecosystem sustainability by preventing nutrient leaching loss after rainfall. Background: Leaching of nutrients (nitrogen and phosphorus) from fertile agricultural ecosystems has become of major global concern because it causes eutrophication of surface water with adverse consequences for human health and water quality. Moreover, losses from infertile ecosystems can reduce plant productivity and ecosystem sustainability if there is no additional nutrient input. Hence, it is of critical importance to understand which mechanisms prevent nutrient loss and retain nutrients inside ecosystems. Besides lateral transport of nutrients via soil erosion and surface runoff, vertical movement through the soil profile (e.g. leaching) has been recognized as an important process contributing to nutrient loss. Until now there are no studies that tested whether mycorrhizal fungi can reduce nutrient losses. This is surprising because mycorrhizal fungi are often very abundant in the soil and play a key role in the nutrient cycle of plant communities. Mycorrhizal fungi can forage highly effectively for nutrients in the soil and, by doing so they could prevent leaching of nutrients (e.g. in winter or during periods with heavy rainfall). Aims: The following key questions are investigated in this project: 1. Can mycorrhizal fungi reduce nutrient loss from experimental grassland? 2. Can arbuscular mycorrhizal fungi reduce nutrient leaching losses at high soil fertility, low temperatures and when rainfall intensity increases? 3. Is ecosystem sustainability (measured as nutrient retention and reduced nutrient loss after rainfall) enhanced by the presence of diverse communities of arbuscular mycorrhizal fungi? Relevance: It has been reported that the available phosphate sources will be depleted in about 50 years and some authors suggest that we will face a phosphate crisis endangering agricultural production. Thus, it is of critical importance to understand whether mycorrhizal fungi can reduce phosphorus loss from soils. Moreover, the production of nitrogen fertiliser is energetically expensive and high levels of nitrate in groundwater are of concern because they can pose a significant health risk and have a negative impact on downstream ecosystems. Hence, this shows that there is a need to better understand which factors influence the N-cycle and reduce N-losses.