Plant phenology response to nitrogen addition decreases community biomass stability in an alpine meadow

Phenology is a sensitive indicator of plant responses to environmental changes, and its shifts could impact community structure and function. However, the effects of phenological shifts on community stability are poorly understood. We conducted a 4-yr N enrichment and precipitation change experiment to assess their effects on community stability through phenological responses. To do so, we measured phenological duration and overlap (based on leaf-out and flowering phenology of 55 species) in an alpine meadow on the Tibetan Plateau. N enrichment extended the vegetative stage of grasses, sedges, and community by 4.62, 4.72, and 11.74 d, respectively, but shortened that of forbs by 6.14 d and increased the overlap of flowering among individuals within the community. Meanwhile, N enrichment decreased species richness, asynchrony, and stability of sedges. Furthermore, N enrichment decreased community stability by decreasing asynchrony but was not associated with richness. Interestingly, N enrichment also decreased sedges stability by extending their vegetative stage and increasing the overlap of flowering, consequently reducing community stability. Our findings imply that N enrichment reduces phenological compensation and thus threatens grassland stability, which highlights the importance of phenological niches in understanding the maintenance of grassland stability under ongoing climate change.