Active Methanotrophs in Suboxic Alpine Swamp Soils of the Qinghai-Tibetan Plateau.

Methanotrophs are the only biofilters for reducing the flux of global methane (CH) emissions in water-logged wetlands. However, adaptation of aerobic methanotrophs to low concentrations of oxygen and nitrogen in typical swamps, such as that of the Qinghai-Tibetan Plateau, is poorly understood. In this study, we show that like methanotrophs dominate methane oxidation and nitrogen fixation under suboxic conditions in alpine swamp soils. Following incubation with C-CH and N-N for 90 days under suboxic conditions with repeated flushing using an inert gas (i.e., argon), microbial carbon and nitrogen turnover was measured in swamp soils at different depths: 0-20 cm (top), 40-60 cm (intermediate), and 60-80 cm (deep). Results show detectable methane oxidation and nitrogen fixation in all three soil depths. In particular, labeled carbon was found in CO enrichment (C-CO), and soil organic carbon (C-SOC), whereas labeled nitrogen (N) was detected in soil organic nitrogen (SON). The highest values of labeled isotopes were found at intermediate soil depths. High-throughput amplicon sequencing and Sanger sequencing indicated the dominance of -like methanotrophs in swamp soils, which comprised 21.3-24.0% of the total bacterial sequences, as measured by C-DNA at day 90. These results demonstrate that aerobic methanotroph is the key player in suboxic methane oxidation and likely catalyzes nitrogen fixation in swamp wetland soils in the Qinghai-Tibetan Plateau.