Supplementary material from "Contrasting temporal stability responses of tall and short grassland species to a decade of nitrogen addition"

Nitrogen enrichment often reduces plant diversity and temporal stability at the community scale. However, tall and short species occupy distinct microhabitats and employ different adaptive strategies, raising the possibility of divergent responses to nitrogen. Using a 13-year experiment (2011–2023) in an alpine meadow on the Qinghai–Tibet Plateau, we examined how nitrogen addition influences species diversity (richness, evenness) and temporal stability of biomass in tall versus short species. We found that nitrogen enrichment has opposing effects on tall and short species. Specifically, nitrogen enrichment increased temporal stability of tall species, mainly by increasing species asynchrony. In contrast, nitrogen addition decreased temporal stability of short species through decreasing both species asynchrony and species stability, and these changes were mediated by a reduction in species richness. At the community scale (i.e., tall and short species combined), the negative effects of nitrogen addition on diversity and stability were driven by the responses of tall species, short species, and the compensatory dynamics between them. By partitioning species according to height, our study reveals contrasting trait-based responses to nitrogen enrichment and highlights the importance of key attributes such as plant height in shaping biodiversity–stability relationships under global change.