Elevational patterns of plant species and phylogenetic diversity in the eastern Pamir Plateau

Mountain ecosystems offer natural gradients for exploring biodiversity patterns; however, the elevational patterns of plant species and phylogenetic diversity in the eastern Pamir Plateau remain poorly understood. As a biogeographical junction of the Central Asian mountain ranges, the eastern Pamir Plateau in China is geographically connected to the main part of the Pamir Plateau in Tajikistan, resulting in significant climatic and topographical heterogeneity and unique regional vegetation communities. In this study, we established 5 elevational transects and 91 plots (1500–4870 m) in the eastern Pamir Plateau to investigate the patterns and environmental drivers of plant diversity at both regional and local spatial scales. We examined diversity patterns and community composition using regression models and community structure analysis and quantified the relative importance of environmental factors using a random forest model. The results showed a distinct differentiation along elevation gradients, with overall plant diversity, herbaceous plant diversity, and phylogenetic diversity index increasing with elevation, whereas woody plant diversity declined. The phylogenetic structure indices (including net relatedness index and nearest taxon index) exhibited heterogeneous elevational responses, indicating that community assembly was jointly driven by environmental filtering and niche differentiation. Soil nutrients, water availability, and temperature were the primary environmental drivers, with soil factors predominantly influencing herbaceous plant diversity, while climatic variables dominated woody plant diversity. These findings demonstrate that plant diversity along elevational gradients of the eastern Pamir Plateau exhibits the characteristic patterns of a unique arid mountain ecosystem, where enhanced soil fertility and moderate moisture at higher elevations partly offset energy limitations, thereby maintaining plant diversity through functional convergence of closely related lineages. This pattern of biodiversity maintenance contrasts with the divergence-driven community assembly processes commonly observed in humid mountain systems. Overall, this study contributes to a better understanding of biodiversity maintenance in the eastern Pamir Plateau. Given its geographical continuity with the Pamir Plateau in Tajikistan, our findings can provide a basis for alpine conservation efforts across arid Central Asia.