Seasonal dynamics of sedimentary dissolved organic matter in plateau lakes: Driving effects on microbial community...

Plateau lakes, as sensitive zones to global climate change and critical hubs for land-water carbon exchange, remain understudied in terms of the seasonal dynamics of their sedimentary dissolved organic matter (DOM) and its interactions with microbial ecological function. This study employed Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and metagenomic techniques to unravel the seasonal variations of DOM and their regulatory roles in microbial community and elements cycling. During the dry season, low water temperature (WT), dissolved oxygen (DO), and high electrical conductivity (EC) promoted accumulation of lignin-like and carboxyl-rich aliphatic molecules (CRAMs), with Fuxian Lake exhibiting the strongest sequestration. The subsequent wet period raised microbial biomass carbon (MBC) and easily oxidizable organic carbon (EOC), lowered average mass-to-charge ratios and increased both nominal hydrogen-to-carbon ratios (H/C) and the molecular lability index (MLB%). Labile sugars and peptides enhanced microbial α-diversity, whereas refractory compounds selected for specialist taxa and intensified community differentiation. Random forest identified sugars, peptides, O₃S + O₅S, biological index (BIX), and WT as core drivers of element cycling genes expression. Functional gene modules diverged along trophic status. The oligotrophic deep lake underwent seasonal turnover, whereas the eutrophic shallow lake preserved stable supermodules integrating multiple metabolic pathways to buffer perturbations. Anthropogenic disturbances elevated sulfur/nitrogen-containing heteroatomic compounds and threatened sediment carbon sinks and element cycling balance. This study advances the understanding of DOM-driven biogeochemical cycles and provides a scientific framework for managing multi-element interactions in climatically sensitive plateau lakes.