Enhanced plant diversity reduces nitrous oxide emissions in forest soils worldwide

Forests are recognized as the largest natural source of nitrous oxide (N2O) emissions on land, with deforestation drastically reducing the cover and biodiversity of native forests worldwide. Yet, how losses in forest biodiversity affect soil N2O fluxes remains poorly understood. Here, we combined a global tree diversity-forest soil N2O data set, including 201 paired comparable observations from global forests, with a three-year field survey of in-situ flux data gathered from a long-Term plant diversity field experiment. Our analyses reveal that tree diversity has a significant negative effect on soil N2O emissions, primarily driven by a decrease in N2O production associated with denitrification. More specifically, we showed that reductions in N2O emissions with tree diversity can be attributed to a decrease in the availability of soil inorganic nitrogen. Predictive modeling further shows that compared to forests with a single tree species, forests with two tree species can reduce global forest N2O emissions by 10.39%, while those with 24 tree species achieve the maximum mitigation effect, reducing emissions by 56.30%. Taken together, our work highlights the contribution of tree diversity for mitigating N2O emissions, highlighting the importance of accounting for biodiversity when reforesting old forests and supporting new afforestation processes.