Nitrogen enrichment and warming shift community functional composition via distinct mechanisms: The role of intraspecific trait variability and species turnover

Global change factors may shift community functional composition by driving species turnover (species occurrence and species relative abundance) and intraspecific trait variability. However, their relative contribution in determining the functional response of community to global change, especially nitrogen enrichment and warming, remains unclear. We conducted a fully factorial field experiment in a Tibetan alpine meadow to examine the responses of plant community functional composition to nitrogen enrichment and warming by quantifying seven plant functional traits in each plot. Using the sum of squares decomposition, we further disentangled the relative contribution of intraspecific trait variability and species turnover to changes in community functional composition. We found that nitrogen enrichment caused a shift of plant community towards a more resource‐acquisitive strategy, while warming resulted in a shift towards a more resource‐conservative strategy. Plant intraspecific trait variability controls shifts in community functional composition in response to nitrogen enrichment, whereas species turnover (especially change in species relative abundance) mainly explains warming‐induced shifts. Nitrogen enrichment and warming did not show significant interactive effects on plant functional composition. These findings suggest that nitrogen enrichment and warming can alter community functional composition of alpine meadow through distinct mechanisms. Plant intraspecific trait variability confers functional resilience of Tibetan alpine meadows under nitrogen enrichment, but warming could induce significant turnover of species that pronouncedly impacts community functioning in this highland ecosystem. Read the free Plain Language Summary for this article on the Journal blog.