Cold-Season Precipitation and Latitudinal Differences Are Key Drivers of Salix alba Genetic Diversity in Arid Zones

Salix alba L. (Linnaeus, 1753; Salicaceae), a widely distributed riparian species, remains understudied regarding its genetic diversity patterns and driving factors in arid zone ecosystems. In this study, 320 Salix alba samples were collected from 10 geographic unit groups in Xinjiang, China, a typical arid zone, and analyzed using a comprehensive approach that incorporated SSR molecular marker technology with multi-dimensional data on geographic and climatic factors. The analysis revealed that: (1) The genetic diversity of Salix alba in the arid zone was found to be relatively rich, with populations in the humid areas of northern Xinjiang (e.g., Shannon’s index of I = 0.45 in Ili) significantly higher than those in the extreme arid regions of southern Xinjiang (e.g., Hotan), with I = 0.0762 in Yili. Further analysis using both STRUCTURE (K = 3) and PCoA methods confirmed the division of Salix alba populations in Xinjiang into three independent genetic clusters, with 65% of the observed genetic variation originating from differences between these populations. (2) Secondly, climatic factors exhibited higher explanatory power than geographic factors in elucidating variations in genetic distances among individuals. Cold season precipitation differences (Bio19, r = 0.621) and the coefficient of variation of annual precipitation (Bio17, r = 0.588) were identified as the primary drivers of these variations. Conversely, the latitudinal difference (r = 0.487) and geographic distance (r = 0.207) exhibited a significant impact on genetic distance, underscoring the importance of geo-graphic factors in shaping genetic variation.