Nitrogen deposition magnifies destabilizing effects of plant functional group loss

Terrestrial ecosystems are under threat by the co-occurring biodiversity loss and nitrogen (N) deposition. Awareness is growing that the stabilizing effects of plant diversity on productivity depend on environmental context, but it remains unknown about how the loss of plant functional groups and N deposition interactively influence species richness and community stability. Here we carried out an eight-year experiment of plant functional groups removal and N addition experiment in subalpine meadow. We found that the removal of plant functional groups and N addition interactively affected averaged plant species richness and community stability. Without N addition, the absence of forbs, but not other functional groups, significantly decreased average species richness and community stability through decreasing species asynchrony (i.e., asynchronous dynamics among species under fluctuating conditions). Under N addition, the absence of forbs, grasses and legumes all led to significant declines in average species richness, causing a decrease in community stability by decreasing species asynchrony, among which the absence of forbs had the greatest negative effects on community stability. Moreover, N addition reinforced the destabilizing effects caused by the loss of functional groups. Our findings show that the diverse forbs maintain plant community stability through asynchronous dynamics among species, especially under N deposition scenario. Therefore, we suggest that conservation and restoration of plant communities and their stability would benefit from a functional-group specific strategy by considering the largely ignored forb species, while helps guide conservation management efforts to reduce temporal variability for ecosystem service in the face of uncertain species extinction and N deposition scenarios.