Eutrophication influences methanotrophic activity, abundance and community structure in freshwater lakes

Lake is an important natural source of methane, a potential greenhouse gas, in the atmosphere. Aerobic methanotrophs can consume a notable proportion of the methane produced in lacustrine ecosystems. However, previous studies mainly focused on aerobic methanotrophs in deep and oligotrophic lakes, while little is known about these organisms in shallow and eutrophic lakes. Lake eutrophication leads to more abundant substrates for methanogenesis, and a subsequent higher methane flux. Therefore, the methanotrophs in eutrophic lakes might play a more important role in mediating lacustrine methane emission. In the current study, aerobic methanotrophs in the sediments of two adjacent shallow freshwater lakes at different trophic status (mesotrophic and eutrophic, respectively) were investigated. Abundant methanotrophs and active aerobic methane oxidation were observed in both lakes. While the eutrophic lake harbored a higher abundance of methanotrophs. The result of pmoA-based high-throughput sequencing suggested that methanotrophic communities in the two studied lakes were dominated by unique groups (Type Ib and Type II), dependent on lake and season. But generally, eutrophication might lead to a higher proportion of Type II methanotrophs. The abundance and uniqueness of methanotrophic community could be attributed to lake eutrophication, and were regulated by environmental variables of both sediment and overlying water. This work provides a new insight towards methanotrophs in shallow freshwater lake impacted by eutrophication.