Effects of plant diversity on productivity strengthen over time due to trait-dependent shifts in species overyielding

Using data from 65 grassland and forest biodiversity experiments, we show that the temporal strength of diversity effects at the community scale is underpinned by temporal changes in the species that yield. These temporal trends of species-level overyielding are shaped by plant ecological strategies, which can be quantitatively delimited by functional traits. In grasslands, the temporal strengthening of biodiversity effects on community productivity was associated with increasing biomass overyielding of resource-conservative species increasing over time, and with overyielding of species characterized by fast resource acquisition either decreasing or increasing. In forests, temporal trends in species overyielding differ when considering above- versus belowground resource acquisition strategies. Overyielding in stem growth decreased for species with high light capture capacity but increased for those with high soil resource acquisition capacity. Our results imply that a diversity of species with different, and potentially complementary, ecological strategies is beneficial not only for maintaining community productivity over time in both grassland and forest ecosystems.The datasets contain information for each experiment, interannual climate data, and species-level trait data used in this study. The climate data MAT and MAP were downloaded from ERA5Land (monthly averaged data), and SPEI were accessed from the global SPEI dataset. Trait data were mainly obtained from the Plant Trait Database (TRY), the Global Root Trait (GRooT) database, and site-specific measurements from certain experiments.