Phylogenetic Distribution and Predicted Functional and Ecological Shifts in Soil Bacterial Communities Along a Soda Saline–Alkali Wetland Degradation Gradient

Wetland degradation in soda saline–alkali ecosystems can profoundly alter belowground microbial communities, yet its effects on bacterial phylogenetic distribution and predicted ecological characteristics remain insufficiently understood. This study investigated soil physicochemical properties, enzyme activities, and bacterial communities across a wetland degradation gradient in the Halahai Provincial Nature Reserve, China, including reed wetland (RW), meadow steppe (MS), and degraded Suaeda saline patches (DS). Soil analyses were integrated with 16S rRNA gene amplicon sequencing, phylogenetic reconstruction, and FAPROTAX and BugBase prediction. DS showed significantly higher pH and electrical conductivity, but lower soil water content, organic carbon, nutrient availability, and urease activity than RW and MS. Alpha diversity analysis indicated that DS had lower bacterial richness and diversity, but higher dominance, whereas RW and MS did not differ significantly. Beta-diversity analysis revealed clear habitat-dependent separation, with DS harboring the most distinct community structure. Taxonomic and phylogenetic analyses indicated enrichment of Gemmatimonadota and the RCP2-54 lineage in DS, whereas RW and MS were more strongly associated with Pseudomonadota, Acidobacteriota, and related groups. Predicted functional and phenotypic analyses further suggested a shift toward stress-related and degradation-associated traits in DS. These findings demonstrate that wetland degradation reshaped the taxonomic composition, phylogenetic distribution, and predicted ecological characteristics of soil bacterial communities in this fragile ecosystem.