Depth-Related Patterns and Physicochemical Drivers of Soil Microbial Communities in the Alpine Desert of Ngari, Xizang

The Beishan region near Shiquanhe Town in Ngari, western Xizang (Tibet), represents a typical alpine desert ecosystem on the Qinghai-Xizang Plateau. However, depth-related patterns of soil microbial communities and their physicochemical controls remain insufficiently understood. Here, microbial community composition and functional attributes were examined across three soil horizons-topsoil (0-20 cm), subsoil (20-40 cm), and deep subsoil (40-60 cm)-sampled in May 2024 prior to artificial greening. High-throughput 16S rRNA and ITS sequencing combined with physicochemical analyses revealed clear vertical stratification: bacteria were dominated by Proteobacteria and Actinobacteriota, and fungi by Ascomycota. Bacterial diversity was higher in the topsoil, whereas fungal diversity exhibited a gradual increase with soil depth; however, these trends did not reach statistical significance (<i>p</i> > 0.05). Functional predictions indicated predominantly aerobic heterotrophic bacteria and a shift from pathogenic to saprotrophic fungi with depth. Multivariate analyses (RDA, CCA, BRT) consistently identified soil pH and moisture as fundamental habitat constraints, and organic carbon, available phosphorus, and available potassium as physicochemical drivers with nonlinear threshold responses. These results highlight soil pH, moisture, and nutrient status (N, P, K) as primary determinants of microbial community assembly and provide guidance for microbially informed ecological restoration in alpine desert ecosystems.