From structure to assembly processes: how salinity regulates soil bacterial communities in arid regions

Although salinity functions as a key environmental filter for soil microorganisms, its comprehensive effects on soil microbial community structure and assembly processes remain poorly understood, particularly in arid regions prone to salinization. In this study, soil bacterial communities along a natural salinity gradient at the edge of Ebinur Lake in Northwest China were investigated. Using 16S ribosomal RNA (16S rRNA) sequencing, we examined variations in soil bacterial community structure, co-occurrence patterns, and assembly mechanisms across different soil salinity groups, including lightly salinized soils (LSS), moderately salinized soils (MSS), and heavily salinized soils (HSS). The results showed that soil bacterial diversity varied significantly among salinity groups, with the highest value observed in LSS. Community dissimilarity increased notably with greater variations in salinity. Notably, a systematic shift in soil bacterial composition occurred along the salinity gradient, with salt-sensitive bacterial phyla (e.g., Acidobacteria and Gemmatimonadetes) being progressively replaced by salt-tolerant ones (e.g., Firmicutes and Bacteroidetes). Network analysis underscored that increased salinity led to reduced soil bacterial network complexity and stability. More positive correlations among soil bacteria occurred in HSS, suggesting a potential shift toward cooperative microbial strategies under severe salt stress. Moreover, the assembly processes governing soil bacterial communities transitioned from stochastic process, predominantly in LSS (71.43%) and MSS (80.00%), to deterministic process in HSS (66.66%). In summary, the results emphasize the multifaceted role of soil salinity in shaping soil bacterial communities in arid ecosystems, thereby enhancing the understanding of the impacts of soil salinization on soil microbial dynamics.