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), despite its considerable role in modulating community dynamics, which may largely mislead the inference of community assembly. Under simulated extreme droughts in a temperate steppe, we integrated ITV and interspecific trait variation for four key traits, plant height (Height), specific leaf area (SLA), leaf dry matter content (LDMC), and leaf thickness (LT), to examine how drought alters functional niche structure and underlying processes. Drought shifted communities toward conservative resource-use strategies, reduced community variation in LT, and interspecific trait overlap in terms of SLA, LDMC, LT, and the multivariate trait space, whereas community-level ITV remained stable across all traits. These changes were driven primarily by diversity loss and increases in the 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 advance our understanding of the paradigm of trait convergence under environmental filtering. Drought-induced diversity loss amplifies functional niche differentiation, underscoring the critical role of species reorganization through dominance shifts, with little evidence for intraspecific trait plasticity in mediating community assembly under climate extremes.