Endogenous methanogenesis stimulates oxidation of atmospheric CH4 in alpine tundra soil

Experiments were done to test the hypothesis that atmospheric CH4 oxidizers in a well-drained alpine tundra soil are supported by CH4 production from anaerobic microsites in the soil. Soil was subjected to 22 days of anaerobic conditions with elevated H-2 and CO2 in order to stimulate methanogenesis. This treatment stimulated subsequent atmospheric CH4 consumption, probably by increasing soil methanogenesis. After removal from anaerobic conditions, soils emitted CH4 for up to 6 h, then oxidized atmospheric CH4 at 111 (+/-5.7) pmol (g dry weight)(-1)h(-1) which was more than 3 times the rate of control soils. Further supporting our hypothesis, additions of lumazine, a highly specific inhibitor of methanogenesis, prevented the stimulation of atmospheric CH4 oxidation by the anaerobic treatment. The method used to create anaerobic conditions with elevated H-2 and CO2 also elevated headspace CH4 concentrations. However, elevated CH4 concentrations under aerobic conditions did not stimulate CH4 oxidation as much as preexposure to H-2 and CO2 under anaerobic conditions. Anaerobic conditions created by N-2 flushing did not stimulate atmospheric CH4 oxidation, probably because N-2 flushing inhibited methanogenesis by removing necessary precursors for methane production. We conclude that anaerobic conditions with elevated H-2 and CO2 stimulate atmospheric CH4 oxidation in this dry alpine tundra soil by increasing endogenous CH4 production. This effect was prevented by inhibiting methanogenesis, indicating the importance of endogenous CH4 production in a CH4_ consuming soil.