Shifts in dominant species modulate nitrogen effects on community temporal stability along a degradation gradient in Tibetan alpine grasslands

Grassland degradation is a widespread concern globally. Nutrient addition is widely recognized as an important management measure for degraded grassland restoration, but nutrient inputs may have important effects on temporal stability of communities. However, it is unclear how the degradation degrees regulate the impacts of adding nitrogen (N) on temporal stability of communities due to large variations in community composition and soil nutrient content. Herein, long-term experimental study was used to identify the N influences on temporal stability of community and driving factors of alpine grasslands at three degradational stages (none (ND), moderate (MD), and heavily degraded grassland (HD)). Elevated N could significantly enhance the aboveground biomass of ND, while there was no notable effect on MD and HD. However, N addition significantly lowered the temporal stability of all these three grasslands, although species richness was only pronouncedly reduced in MD. Our most conspicuous outcome is the major mechanism of temporal stability of community varied with degradation stages. N addition decreased temporal stability of the community predominantly by decrease in the richness of species and the stability of dominant species in ND and MD while decrease in dominant species stability, asynchrony, and richness of species in HD. This study highlights that impacts of N enrichment on temporal stability of community are potentially intermediated via community composition of alpine grasslands, which can offer guidance for scientific management and rehabilitation of degraded alpine grasslands.