Many of the processes that determine the distributions of plant species and the functioning of ecosystems take place belowground. However, while many studies have focussed on aboveground functional traits of plants, belowground functional traits have been largely ignored. Clearly, data on root traits of large numbers of plant species are needed to better understand biodiversity patterns. Therefore, we propose to assess root functional traits and fungal endophyte infection for the approximately 350 flowering plant species that occur in the 150 grassland experimental plots (EPs) of the Biodiversity Exploratories. In several experiments, plants of these species will be grown to measure root morphology, plasticity in root morphology (in response to fertilizer addition), net uptake capacities of different nitrogen forms and fungal endophyte infection. We will then use these data, in combination with other data from the Biodiversity Exploratories, to test how occurrence frequency and abundance of the species relates to functional root traits, whether there is a match between functional root traits and environmental variables, such as land-use intensity, and how measures of belowground functional diversity relate to aboveground functional diversity and ecosystem functions.