Soil salinity and moisture have contrasting effects on deterministic versus stochastic assembly of bacterial communities in alpine lake shores

The lakeshore zone represents a crucial component of the lake ecosystems, highly susceptible to the properties of lake water. However, microbial community structure and assembly mechanisms in lakeshore soils across differing lake salinities remain poorly understood, particularly involving microbial generalists and specialists. Here, we sampled lakeshore soils from three lakes on the Qinghai-Tibet Plateau: a freshwater lake (Yang Lake, YL), a brackish lake (Qinghai Lake, QHL) and a saline lake (Chaka Lake, CKL). Using 16S rRNA gene sequencing, we investigated bacterial diversity, co-occurrence patterns and assembly processes across these lakeshore soils under three distinct environmental conditions. Results showed that soil salinity and moisture were the most important factors influencing bacterial community composition, with diversity and network complexity decreasing as salinity increased while the opposite trend for moisture levels. CKL soils harbored the lowest bacterial gene copy number and diversity, yet the highest relative abundance of Gemmatimonadota, indicating their tolerance to high salinity. In contrast, the excessive moisture in YL and QHL soils probably promoted hypoxic conditions, leading to the blooming of Desulfobacterota and MBNT15 phyla. While stochastic processes predominantly influenced bacterial community assembly in YL and QHL soils, with goodness of fits of the Sloan neutral model being 0.74 and 0.63 respectively, their influence drastically decreased in CKL (goodness of fit = 0.17) soils. This reduction could be attributed to the strong selective pressures of high salinity and low water content in CKL soils, which led to greater environmental heterogeneity. Furthermore, generalists and specialists exhibited distinct ecological strategies, with specialists demonstrating greater network complexity maintenance and generalists being more influenced by stochasticity and likely to preserve network stability. Overall, this study highlights that soil salinity and moisture co-mediated the role of stochasticity on shaping bacterial communities, which deepens our understanding of the processes maintaining microbial diversity in alpine lakeshore ecosystems.