"The role of biodiversity for the functioning of ecosystems and the provisioning of ecosystem services is a key issue in ecology. Both in natural ecosystems and in agriculture legumes are critical for enhancing ecosystem productivity because of their ability to fix aerial nitrogen (N). Many studies have tested how non-leguminous plants may benefit from legumes, however, a main and unresolved question is whether and how legumes can benefit from growing with non-leguminous species. This question is central in my proposed research. Models predict that increased N input from legumes will feed back to suppression of legumes by non-leguminous species that are better competitors for light, which suggests that legumes will perform best in monocultures. However, field observations indicate that productivity of legume monocultures is unstable and that legumes must have an advantage of growing in mixtures with non-leguminous species. It has been suggested that interactions with soil organisms are critical in explaining why legumes persist poorly, but whether non-leguminous species can modify soil properties to the benefit of legumes remains to be tested. The aim of my proposal is to unravel how leguminous grassland species may benefit from growing with non-leguminous species through interactions with abiotic (resources) and biotic (detrimental and beneficial) soil components and whether enhancement of legumes results in increased plant community productivity and nutrient retention. My three specific study objectives are: 1. How aboveground and belowground traits of leguminous species and non-leguminous species may promote complementary use of resources 2. How non-leguminous plants may suppress root herbivores of the legumes and 3. How non-leguminous plants may promote positive effects of root mutualistic symbionts. The main benefits of the program for my career are enhanced independency, experience in cutting-edge techniques and coaching in acquiring funding."