Tree species richness improves soil net nitrogen mineralization rates in a young biodiversity-ecosystem function experiment

Forest ecosystems are facing declining plant species diversity. However, the effects of reduced tree species diversity on soil nutrient supply and tree productivity remain poorly understood. We conducted a biodiversity-ecosystem function experiment with a range of subtropical tree species richness (1, 4, 8, 16, and 32) to investigate the impacts of tree species diversity on soil net nitrogen (N) mineralization rates and its regulation on tree productivity in a young subtropical forest experiment. Our findings indicate a log-linear trend between soil net N mineralization rates and tree species richness, potentially suggesting an improvement in soil N supply capacity with greater species richness. Leaf N content, soil water content and peroxidase enzyme activity were identified as primary positive predictors influencing soil net N mineralization rates. In monoculture forests, soil net N mineralization rates were negatively correlated with litter production and tree basal area, while no such correlation was observed in mixed forests. This implies that soil net N mineralization rates play a critical role in tree productivity for monoculture forests. Together, these results provide strong evidence that the rate of decrease in soil nutrient supply capacity potential accelerates with the loss of tree species diversity in young tree communities, and highlights the importance of increasing tree species diversity to mitigate nutrient limitations. Therefore, preserving tree species diversity is crucial for the future functionality of ecosystems amidst global biodiversity loss.