Diversity effects under different nutrient addition and cutting frequency environments in experimental plant communities

The effects of biodiversity on productivity have been well studied in the past decades. However, the responses of these biodiversity effects to modern grassland managements have not been explicitly tested. By establishing a five years diversity-manipulated experiment with different cutting frequency and nutrient addition levels, we explored the changes of biodiversity effects and the underlying mechanisms under these managements. Our results showed that community biomass increased with species richness. The correlations were observed under all management regimes, but their strengths varied with management intensity. The net biodiversity effects (NE) increased with nutrient supply, but reduced with frequent cutting. These two factors also interactively influenced NE. Importantly, their influences could last 5 years or longer. The NE changes mainly resulted from the variations of complementarity effects (CE), i.e., the aboveground space partitioning of our species. However, the selection effects (SE) were minimally influenced by nutrient addition and cutting frequency, indicating that under these conditions our species had comparably competitive strength. Especially, CE increased over time in highly cutting subplots, suggesting that this relationship was condition-dependent. We conclude that biodiversity is vitally important for ecosystem functioning even when the ecosystems are disturbed by human activities, and is most effective in enhancing biomass productivity under nutrient supply and low cutting frequency conditions. Field studies with species that come from other functional groups are needed to draw a more general conclusion.