Ammonium Impacts Methane Oxidation and Methanotrophic Community in Freshwater Sediment

Lacustrine ecosystems are regarded as one of the important natural sources of greenhouse gas methane. Aerobic methane oxidation, carried out by methane-oxidizing bacteria, is a key process regulating methane emission. And ammonium is believed to greatly influence aerobic methane oxidation activity. To date, disagreement exists in the threshold of ammonium effect. Moreover, knowledge about how aerobic methanotrophic community composition and functional gene transcription respond to ammonium is still lacking. In the present study, microcosms with freshwater lake sediment were constructed to explore the effect of ammonium level on aerobic methanotrophs. Methane oxidation potential, and the density, diversity and composition of pmoA gene and its transcripts were examined during 2-week incubation. A negative impact of ammonium on aerobic methane oxidation potential and a positive impact on pmoA gene density were observed only at a very high level of ammonium. However, pmoA gene transcription increased notably at all ammonium levels. The composition of functional pmoA gene and transcripts were also influenced by ammonium. But a great shift was only observed in pmoA transcripts at the highest ammonium level.