Hydrological Seasonality Drives DOM–Bacteria Interactions in the Rushan River Basin

To unravel hydrological controls on dissolved organic matter (DOM)-microbe interactions in river ecosystems, this study integrated 3D excitation-emission matrix spectroscopy (3D-EEMs), parallel factor analysis (PARAFAC), and 16S rRNA sequencing to characterize seasonal DOM dynamics and microbial assembly in China's Rushan River Basin. PARAFAC resolved contrasting DOM signatures between dry (four protein-like, two humic-like components) and wet seasons (three protein-like, three humic-like components). Dry-season DOM was dominated by tyrosine-like substances (58.03%), reflecting microbial degradation and phytoplankton activity, while wet-season DOM showed elevated tryptophan-like components (34.38%) and terrestrial fulvic acids (17.14%), which may be related to rain-driven external inputs. The α -diversity of the microbiota is relatively high in the wet season, mainly consisting of <i>Proteobacteria</i> (34.06-68.10%) and <i>Actinobacteriota</i> (9.15-20.76%). In the dry season community, there are <i>Bacteroidota</i> (14.71-38.45%) and <i>Verrucomicrobiota</i> (6.13-14.32%). The structural equation model (SEM) semi-quantified the comprehensive pathways by which microorganisms inhibit unstable proteins and enhance humification. These results reveal the synergistic regulatory role of hydrological seasonality on DOM and microorganisms, and provide a basis for adaptive water quality management.