Microbial Diversity and Community Drivers in Caohai Lake (Guizhou, China) Revealed by 16S rRNA Gene Sequencing

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Microorganisms are sensitive indicators of aquatic environmental quality and ecosystem stability. Caohai Wetland, a typical subtropical plateau karst wetland suffering ecological degradation under combined natural-anthropogenic disturbances, is one of the three major plateau freshwater lakes in China and a critical wintering habitat for the Black-necked Crane (Grus nigricollis) along the East Asian–Australasian Flyway. Previous research has focused mainly on phytoplankton, aquatic plants, birds, and the water environment, while knowledge of its microbial community, especially the joint controls of multi-factor hydro-environmental conditions and aquatic plants across the whole lake, remains limited. To determine the diversity and seasonal dynamics of the microbial community and the key environmental factors driving it, water samples were collected from 17 sites in Caohai Lake across four seasons during 2022–2023 and analyzed by 16S rRNA gene sequencing, combined with measurements of hydro-physicochemical parameters and aquatic plant biomass and coverage. Among the 1370 ASVs obtained, the top five phyla in descending order of abundance were Pseudomonadota (45.04%), Bacillota (21.75%), Bacteroidota (11.82%), Actinomycetota (11.09%), and Verrucomicrobiota (3.65%). The microbial community exhibited significant seasonal variations, with richness, the Shannon-Wiener index, and Pielou’s evenness all significantly higher in autumn than in the other three seasons and lowest in spring. Correlation analysis indicated that water temperature was the primary driver of microbial community structure, while SD, EC, and COD also exerted significant influences; in addition, aquatic plant biomass and coverage were identified as key environmental factors shaping the microbial community composition in Caohai. This study provides fundamental monitoring data to support the assessment of the evolutionary trends of the Caohai wetland ecosystem and its conservation and management.