Past Extinction and Contemporary Environment Jointly Shape the Plant Diversity Pattern in the Yarlung Zangbo River Basin, Tibet

Unraveling the drivers of diversity patterns is foundational to effective plant conservation and maintaining ecosystem stability. The Yarlung Zangbo River Basin (YZRB), a globally recognized biodiversity hotspot and Tibet’s most critical ecosystem, supports exceptional plant diversity, yet the spatial patterns of plant diversity distribution and their underlying mechanisms across the entire basin have not been systematically validated. To address this gap, we compiled a comprehensive plant dataset covering 39 counties in the YZRB, integrating multiple data from global/national databases (e.g., GBIF, NSII), authoritative floras (Flora of China, Flora Xizangica), and field surveys. We then characterized patterns of species richness (α diversity) and community compositional differences (β diversity) across key functional groups, including woody vs. herbaceous plants and wide-ranged vs. narrow-ranged species. Our results demonstrated that species richness declines from the humid southeastern to the arid northwestern YZRB, a pattern primarily shaped by hydrothermal conditions (e.g., mean annual precipitation and temperature) and topographic heterogeneity (e.g., elevation range). In contrast, β diversity (and its two components: turnover and nestedness) peaks in the basin’s middle reaches, shaped by environmental filtering and nestedness driven by historical glacial extinctions and incomplete post-glacial recolonization. This is the first systematic, basin-wide validation of plant diversity patterns in the YZRB. The study highlights the importance of contemporary environmental filtering and historical climatic processes in shaping basin-scale plant diversity, providing critical scientific support for targeted conservation strategies.