Turnover of microbial specialists and generalists shapes deterministic assembly and network stability along a...

Salinity-alkalinity gradients impose strong environmental filtering on soil microbial communities, yet the respective roles of generalist and specialist taxa in community assembly and stability remain insufficiently understood in wetland ecosystems. Here, bacterial and fungal communities were investigated across low, moderate, and high saline-alkaline zones in the Luyang Lake wetland, China. Amplicon sequencing was integrated with niche breadth analysis, community assembly inference, co-occurrence network analysis, cohesion metrics, and partial least squares path modeling to assess how generalists and specialists responded to environmental variation and contributed to microbial stability. Bacteria contained a larger generalist pool, whereas fungi were relatively enriched in specialists. Generalists were positively associated with nutrient availability and negatively associated with saline-alkaline stress, while bacterial specialists showed the opposite trend. Niche breadth decreased with increasing salinity-alkalinity, especially in bacteria, and this narrowing was accompanied by stronger deterministic assembly, mainly homogeneous selection. Network analysis further suggested that generalists contributed more to overall community connectivity, whereas specialists became more important for network organization under stronger saline-alkaline stress. Path modeling indicated that bacterial and fungal community stability was associated with distinct response pathways. Overall, salinity-alkalinity reorganized microbial communities by reducing niche breadth, strengthening deterministic assembly, and shifting the relative contributions of generalists and specialists to community stability. These findings improve our understanding of how niche strategy mediates microbial assembly and stability in saline-alkaline wetland soils.