Species interactions alter with environmental change, which influences the relationship between biodiversity and ecosystem functioning (BEF). How BEF relationships change with environments requires knowledge of the changes of functional attributes in individual species in response to environmental change. Here, we assembled experimental plant communities with different species richness (1, 2, 4, 8, and 16) and exposed them to a drought stress gradient (control, moderate and intensive drought stress). Functional redundancy decreased with increasing drought stress...