Common Species Stability and Species Asynchrony Rather than Richness Determine Ecosystem Stability Under Nitrogen Enrichment

Global nitrogen (N) deposition generally reduces ecosystem stability. However, less is known about the responses of ecosystem stability and its driving mechanisms under different N addition gradients. We conducted a four-year N addition experiment in an alpine meadow, using six levels of N addition rates (0, 2, 4, 8, 16, 32 g N m(-2) year(-1)) to examine the effects of N addition on plant community biomass stability and the underlying mechanisms. We found that the stability of ecosystem aboveground net primary productivity (ANPP) decreased linearly with increasing N addition rates, even though it had no effect on plant species richness at low N addition rates and significantly reduced species richness at high N addition rates. The most remarkable finding is that the main mechanism underlying ecosystem stability shifted with N addition rates. The decrease of common species stability contributed most to the reduction of plant community biomass stability under low N addition rates (N0-N4), whereas the decrease of species asynchrony contributed most to the reducing plant community biomass stability under high N addition rates (N8-N32). Our results indicate that species diversity was not a significant predictor of plant community biomass stability in this alpine meadow, which challenges the traditional knowledge. This study highlights the shifts of main mechanism regulating plant community biomass stability under different N addition rates, and suggests that continuous nitrogen deposition in the future may reduce ecosystem stability and potentially impeding the sustainable provision of ecosystem functions and services.