Nutrient enrichment weakens community temporal stability via asynchrony and species dominance in a subalpine grassland

Rapid and frequent nitrogen (N) and phosphorus (P) inputs have seriously disrupted the stability of many ecosystems, prompting us to find the main mechanisms driving these changes across various ecological systems, which is crucial for predicting ecosystem responses to reactive nutrient inputs. While the mechanisms underlying N-induced stability have been extensively studied, the effects of P and simultaneous N and P enrichment on ecological stability and their driving mechanisms are less understood, particularly in alpine ecosystems. To address this gap, we conducted a short-term (2019–2023) simulation experiment of N and P enrichment in a subalpine grassland of Qilian Mountain to evaluate the effects of nutrient enrichment on ecosystem stability and to identify its potential mechanisms. Our findings demonstrated that five-year nutrient enrichment did not obviously affect species richness/dominance, but N+P enrichment significantly decreased both community aboveground biomass (AGB) and the AGB of dominant species. In addition, community temporal stability was strongly reduced with both N and N+P enrichment. This negative impact was directly driven by the stability of dominant species, species dominance, and compensatory effects, which together explained 77 % of the variation in stability according to structural equation modeling (SEM). Moreover, species richness indirectly influenced community stability through species asynchrony. Our findings provide a theoretical basis for understanding the roles of compensatory effects and dominant species in driving changes in ecosystem stability under nutrient enrichment.