Abstract
Thermal stratification drivers of microbial community organization and functional potential in deep lakes, yet comparative analyses of epilimnetic and hypolimnetic microbiome dynamics remain limited. In this study, we combined 16S rRNA gene sequencing with functional microarray (GeoChip 5.0) to investigate stratification-induced shifts in microbial community composition and functional structure in Lake Fuxian, a deep monomictic plateau lake in Yunnan Province, Southwest China. Our analyses revealed a partial decoupling between taxonomic and functional diversity across water layers: the oxygen-depleted hypolimnion harbored higher bacterial taxonomic richness and distinct taxa (Nitrospirae, Parcubacteria, and Thaumarchaeota), whereas the epilimnion exhibited greater functional gene richness with lower beta diversity, indicating enhanced metabolic flexibility. Molecular ecological network analysis uncovered contrasting interaction patterns, with hypolimnetic communities exhibiting greater complexity and modularity. Notably, the Chloroflexi-associated amyA gene emerged as a module hub in hypolimnetic functional molecular ecological networks while distinct connector taxa characterized both epilimnetic and hypolimnetic species molecular ecological networks. Multivariate analyses identified dissolved oxygen and nutrient availability as key environmental drivers of vertical microbial stratification. These findings elucidate microbial adaptation to stratified conditions and underscore the distinct roles of epilimnetic and hypolimnetic communities in biogeochemical cycling in deep lakes experiencing climate-mediated thermal regime shifts.