Diversity–multifunctionality relationships shift with increasing aridity in grasslands

Grasslands, a dominant global ecosystem, face an uncertain future. Diverse grasslands can maintain multiple functions (multifunctionality); however, the relative roles of species diversity and functional diversity in promoting this resilience remain unclear. We examined how the diversity–multifunctionality relationships varied with species diversity and functional diversity at 104 dryland sites under increasing aridity. Positive diversity–multifunctionality relationships strengthened with increasing aridity but waned when aridity levels exceeded 0.83. Functional diversity was more associated with multifunctionality under wetter conditions, but under drier conditions, species diversity became a stronger predictor. Increasing aridity reduced multifunctionality primarily by suppressing plant diversity, particularly under drier conditions. These findings suggest that aridity shifts the mechanism of diversity in maintaining multifunctionality, from functional complementarity to environmental filtering and retention of stress-tolerant taxa, rather than merely altering species richness. Conserving grassland communities that retain stress-tolerant taxa will be critical for sustaining multifunctionality as drylands expand under climate change.