Salinity-driven nonlinear responses of microbial functional genes in sediment biogeochemical cycling across a salt lake gradient.

Salinity is a major environmental driver in saline lake ecosystems, yet the functional genes responses underlying sediment biogeochemical cycling remain poorly resolved. Here, we investigated microbial community composition and functional gene dynamics along a pronounced salinity gradient in Yuncheng Salt Lake. Salinity strongly restructured microbial assemblages, producing distinct taxonomic groups dominated by IMPORTANCE: Salinization is increasing globally in inland waters and can substantially alter microbial processes that regulate sediment biogeochemistry. However, how microbial functional genes governing carbon, nitrogen, phosphorus, and sulfur cycling respond to salinity gradients remains poorly resolved. By examining microbial communities and functional genes across a natural salinity gradient in salt lake sediments, this study demonstrates that salinity not only restructures microbial communities but also drives nonlinear changes in functional gene assemblages. The strong association between taxonomic turnover and functional gene divergence indicates that shifts in microbial community composition are closely linked to changes in functional potential. Identifying salinity as the dominant driver of functional gene organization provides new insights into how salinization may influence microbially mediated biogeochemical processes in saline environments. Together, these findings enhance our understanding of microbial functional dynamics in salt lake sediments and offer a framework for predicting ecosystem responses to ongoing environmental salinization.