From resource-rich to resource-poor grasslands: A shift in β-diversity assembly mechanisms from biotic control to abiotic dominance

Understanding beta-diversity drivers is crucial in an era of biotic homogenization, yet whether its assembly mechanisms shift along environmental gradients remains unclear. Through a trait-based approach across Inner Mongolian grasslands, we collected vegetation data from 134 sites (402 quadrats) encompassing both resource-rich and resource-poor grassland types. Accordingly, we integrated measurements of 22 plant economic traits of dominant species, 7 soil properties, species-area relationships, species composition, and aboveground biomass. Results show resource-poor grasslands exhibit a steeper species-area slope (z-value), indicating higher beta-diversity, than resource-rich grasslands. Crucially, drivers shifted fundamentally: biotic factors (e.g., species richness) dominated in resource-rich systems, whereas abiotic filters (e.g., soil C/N, pH) prevailed in resource-poor systems. Stress-tolerant traits correlated with reduced turnover but were subordinate to abiotic filtering. This systematic transition from niche differentiation to environmental filtering provides a mechanistic framework for predicting biodiversity change, emphasizing the need for context-dependent conservation under global change.