Low N addition rates may maintain community stability over time in alpine grasslands

Numerous studies have demonstrated that nitrogen (N) enrichment typically reduces ecosystem stability, yet how low N addition rates influence temporal dynamics of stability remains poorly understood. Here, we examined the temporal effects of different N addition levels (0, 2.5, 5, and 10 g N m−2 year−1) on the stability of aboveground net primary production (ANPP), species richness, species stability, and species asynchrony, and how the relationships among them change with a 7-year experiment in alpine grasslands. Low N addition significantly enhanced the temporal stability of ANPP during the initial years, whereas this positive effect attenuated over time. In contrast, high N addition reduced community stability, independent of temporal changes. Across the entire experimental period, the stabilizing effect of low N addition was primarily driven by increased species asynchrony, whereas the destabilizing effect of high N addition was mainly mediated by decreased species stability. Moreover, greater interannual precipitation variability amplified the negative effect of high N addition on community stability by reducing species asynchrony, which resulted from the enhanced sensitivity of the dominant species, Stipa purpurea, to precipitation fluctuations. The low N input (≤ 2.5 g N m⁻2 year⁻1) may be prioritized to maintain alpine ecosystem stability in the short term, while attention should be paid to its potential cumulative effects over the long term.