Impact and Mechanisms of Microbial Communities and Environmental Factors on the Composition and Structure of DOM in Lake Ice, Water, and Sediments

Microbial communities serve as crucial mediators of dissolved organic matter (DOM) dynamics in seasonally ice-covered lakes. This comparative study of a saline plateau lake (Lake Daihai) and an eutrophic freshwater lake (Lake Wuliangsuhai) revealed distinct winter microbial patterns, with sediment communities exhibiting 2–3 times higher diversity than ice or water habitats. Fluorescence characterization identified fundamental differences in DOM sources, where saline lake DOM showed mixed terrestrial-autochthonous signatures (fluorescence index: 1.4–1.9), contrasting with the strongly microbial-derived DOM (FI > 1.9) in freshwater systems. Vertical profiling demonstrated progressive humification downward through ice layers, while microbial functional predictions indicated sustained amino acid metabolism despite subzero temperatures. The unique halotolerant community structure of the saline lake contrasted sharply with the psychrophilic Flavobacterium-dominated assemblages in freshwater habitats, reflecting differential adaptation to environmental stressors. Dissolved oxygen and salinity emerged as primary drivers of community composition, while phosphorus availability influenced specific functional groups involved in organic matter processing. These findings highlight the resilience of microbial-mediated carbon cycling under ice cover and provide critical baseline data for predicting ecosystem responses to changing winter conditions in inland waters.