Hydrologic drying is linked to dispersion inflation and reduced predictability in alpine wetland bacterial communities

Alpine wetlands store large soil carbon stocks, yet hydrologic drying can reorganize microbial habitats and weaken restoration assessment based only on mean community shifts. We sampled surface soils across a stage-stratified degradation gradient in the Zoige alpine wetland complex on the eastern Qinghai–Tibet Plateau and characterized bacterial communities using amplicon sequencing. Soil water content declined with degradation and was accompanied by losses of soil organic carbon and plant-available phosphorus, defining a coupled hydrology–resource axis. Alpha diversity increased along the degradation gradient, whereas centroid separation in ordination space remained modest. In contrast, within-stage heterogeneity increased strongly, revealing dispersion inflation under drier conditions. Constrained ordination and partial ordination showed that soil water content and resource pools jointly constrained bacterial community turnover, with soil water content retaining an association beyond covarying soil chemistry. A piecewise structural equation model further summarized the major associations among degradation stage, hydrologic state, soil resource pools, community turnover, and within-stage heterogeneity while accounting for sampling year and site structure. Cross-validation showed that absolute prediction error increased with within-stage heterogeneity, indicating that dispersion inflation reduced out-of-sample predictability beyond stage-level summaries. Overall, hydrologic state emerged as an important upstream dimension of wetland degradation, while dispersion and predictability provided complementary indicators of microbial community reorganization beyond mean compositional change.