Multiple plant community attributes promote ecosystem multifunctionality at high thresholds in alpine grasslands

Plant community attributes play a crucial role in maintaining the functioning of terrestrial ecosystems. However, the relative contributions of different plant community attributes to ecosystem multifunctionality (EMF), and their mediating roles in linking climate and soil factors remain unclear, especially in harsh, natural alpine grasslands. We comprehensively evaluated the effects of community taxonomic and functional composition, and plant taxonomic, functional, and phylogenetic diversity, together with climate and soil parameters, on EMF (assessed using both average and threshold approaches based on eight functions) across 95 alpine grasslands covering a 3,000 km transect on the Tibetan Plateau. We identified the pathways through which plant community attributes mediated EMF, as well as the threshold-dependent changes in these relationships. Results showed that plant community attributes outweighed climate and soil conditions in explaining ecosystem multifunctionality. Among multiple plant community attributes, community taxonomic composition played a larger role in maintaining mean EMF. Community taxonomic composition and functional composition (community weighted mean traits) predominantly mediated the effects of climate and soil on mean EMF. In addition, we found that plant community attributes became increasingly important at higher EMF thresholds, whereas the influence of climatic factors declined. Communities characterized by conservative resource-use strategies supported greater multifunctionality at the highest threshold. Overall, our research provides important regional insights of plant community attributes–multifunctionality relationships from alpine grasslands, and highlights urgent conservation implications for preserving and improving community composition to maximize ecosystem multifunctionality in alpine grasslands.