Sources and composition of sediment dissolved organic matter determine the ecological strategies of bacteria in rivers: evidence, mechanism, and implications

PurposeThe changes of bioavailable carbon components in dissolved organic matter (DOM) may stimulate bacteria to alter their ecological strategies. This study aimed to analyze the coupling connections between the core bacterial communities and the organic carbon components in sediment and to discuss the ecological strategies of bacteria in different rivers.MethodsSediment samples were collected from the Duliujian River (DLJ) and Yongdingxin River (YDX) in Tianjin, China. The sources and components of DOM in sediments were analyzed by using excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis, and the sediment bacterial parameters were determined by using the 16S rDNA high-throughput sequencing method.ResultsThe sediment DOM in DLJ is mainly terrigenous, with high humus-like materials (58.69%), and the sediment DOM in YDX is mainly autogenous, with high protein-like materials (65.24%). At the phylum level, the relative abundance of Proteobacteria in the sediment of YDX is significantly higher than that of DLJ (P < 0.01). However, the relative abundance of Actinobacteria in the sediment of DLJ is significantly higher than that of YDX (P < 0.01). At the genus level, Thiobacillus and Halomonas are more abundant in YDX than in DLJ, whereas Pseudomonas, Sphingomonas, Pseudarthrobacter, Haliangium, and Actinomycetales are more abundant in DLJ than in YDX. Co-occurrence network analysis indicates that the core bacterial communities of YDX have a greater network complexity than that of DLJ. Soil major nutrients and pH have no direct effects on the DOM composition, but they have significant effects on the core bacterial communities and/or their metabolic pathways (P < 0.05).ConclusionTerrigenous inputs and humus-like substances of sediment DOM promote the resource utilization capacity of bacteria, which may adapt to external changes by regulating metabolic function, and their carbon capture strategies are determined by metabolic demand.