The ongoing biodiversity crisis is driven by global climate change, like extreme snowstorm and overgrazing, that alters community composition, necessitating a better understanding of community assembly. We investigated the effects of 15-year experimental grazing and snow addition on taxonomic, phylogenetic, and functional diversity on the Tibetan Plateau. Grazing did not alter community structure, but snow addition caused phylogenetic structure to go from randomness to over-dispersion, as lost species were phylogenetically more closely related to residents than to gained species. Functional community clustering remained unchanged due to opposing trends in individual traits. Moreover, functional traits served as a powerful tool underpinning diversity change. Particularly, species with higher leaf dry matter content and lower specific leaf area, which signify a conservative resource-use strategy, had an increased risk of loss and contributed to changes in community structure under snow addition. Finally, this research offers deeper insights into long-term plant dynamics under environmental changes.

Anthropogenic environmental changes are influencing the structure and function of many ecological communities, but their underlying mechanisms are often poorly understood. We conducted a seven-year field experiment to explore the ecological consequences of nitrogen (N) and phosphorous (P) enrichment in a high-altitude Tibetan alpine grassland. The enrichment of both N and P, but not either alone, resulted in increased plant above- and below-ground biomass. By contrast, N, but not P, enrichment reduced species richness, and altered plant phylogenetic diversity and structure. The observed decline in species richness under N addition was driven by the loss of species characterized by high leaf nitrogen content, and associated with higher soil manganese level and greater belowground competition. Our study highlights resource co-limitation of community biomass but not structure of the study grassland, while also identifying soil metal toxicity and belowground competition as important mechanisms driving community changes after nutrient amendment.