Drought-induced plant dominance shift amplifies functional niche differentiation in steppe communities

Trait-based studies on community assembly under environmental change often overlook intraspecific trait variation (ITV), though it matters considerably in modulating community dynamics. By simulating extreme droughts in a temperate steppe, we integrated ITV and interspecific trait variation to examine how drought alters functional niche structure and underlying mechanisms. Drought shifted communities toward conservative resource-use strategies and reduced total trait space and interspecific trait overlap, while ITV remained stable. These changes were driven primarily by species loss and increases in dominance of fewer species, with negligible effects of intraspecific trait plasticity or species turnover. Communities with fewer but more dominant species exhibited smaller trait overlap. Our findings challenge the paradigm of trait convergence under environmental filtering. Instead, drought-induced diversity loss amplifies functional niche differentiation, underscoring the critical role of species reorganization—through non-random species losses and dominance shifts—rather than intraspecific trait plasticity, in mediating community assembly under climate extremes.