Vertical Variation in Soil Bacterial Communities Across Four Contrasting Stands in a Soda Saline–Alkali Wetland Landscape: A Local Case Study with Implications for Future Monitoring

Vertical bacterial variation may be relevant to monitoring soda saline–alkali wetlands, but evidence from replicated habitats remains limited. We examined four contrasting local stands in the Halahai landscape: reed wetland, meadow steppe, degraded Suaeda saline patch, and converted farmland. Six paired locations per stand were sampled at 0–20 and 20–40 cm, yielding 48 samples. Soil properties, enzyme activities, and 16S rRNA gene profiles were evaluated using linear mixed-effects models, ordination, and term-specific restricted PERMANOVA. The degraded saline stand had the highest pH and electrical conductivity and the lowest resource availability, microbial biomass, and bacterial alpha diversity. Farmland showed comparatively high nutrient availability and richness, although conversion effects could not be separated from agricultural management. Sampled stand accounted for 44.50% of community variation, whereas depth and the stand × depth interaction accounted for only 1.67% and 2.78%, respectively. Adjusted depth contrasts within stands were nonsignificant, and dispersion differed among stands. Community composition was associated with combined salinity–alkalinity, moisture, and resource gradients rather than independent effects of individual variables. The findings provide a local ecological baseline and support evaluating paired surface and subsurface sampling in future monitoring, but they do not validate microbial indicators or establish restoration or management outcomes.