[Response of Microbial Community to Natural Organic Matter Input in Lake Sediments]

Increased loads of biogenic and terrestrial natural organic matter into freshwater lakes are projected to be a major consequence of global climate change and cyanobacterial blooms. In this study, the effects of phytoplankton-derived organic matter (POM) and terrestrial humic acid (HA) on the activity, composition, and function of the microbial community in Lake Taihu sediments were investigated. Fluorescent spectra demonstrated that POM with high chemodiversity was composed of labile protein-like components (50%) and recalcitrant humic-like components (50%), while humic-like substances accounted for 97% of HA. Over two-month periods, the organic carbon mineralization in sediments was enhanced owing to increasing NOM concentrations; however, the carbon consumption in POM-amended sediments was significantly higher than that in sediments amended with the same concentrations of HA. Analysis of extracellular polymeric substances indicated that NOM input improved the microbial secretion of proteins and polysaccharides, increasing the aggregation and stability of the microbial community. The amendment of POM also stimulated the activity of organic matter metabolic enzymes, promoting microbial activity. Moreover, 16S rRNA gene sequencing suggested that the mineralization of NOM (especially POM) increased the diversity of the microbial community, favored the survival of Proteobacteria and Bacteroidetes, and upregulated the function genes of organic matter metabolism. These results suggest that the composition and function of microbial community in sediments were associated with the origin, composition, and concentration of NOM input.