Abstract: Elevated atmospheric CO2 concentration may affect the oxidation rate of methane (CH4) in forest soil. In this study, the effects of a 6-year exposure to elevated CO2 concentration (500 μmol·mol-1) on the soil microbial process of CH4 oxidation under Quercus mongolica seedlings were investigated with open top chamber (OTC), and specific 16S rRNA and pmoA gene fragment primers were adopted to analyze the diversity and abundance of soil methanotrophs. Comparing with that under ambient CO2 and open-air, the soil methane consumption under elevated atmospheric CO2 during growth season was reduced by 4% and 22%, respectively. The specific 16S rRNA PCR-DGGE analysis showed that under elevated CO2, the community structure of methane-oxidizing bacteria (MOB) changed, and the diversity index decreased. Elevated CO2 concentration had no distinct effects on the abundance of TypeⅠ MOB, but decreased the amount of TypeⅡ MOB significantly. The pmoA gene copy number under elevated CO2 concentration decreased by 15% and 46%, respectively, as compared with that under ambient CO2 and open-air. Our results suggested that elevated atmospheric CO2 decreased the abundance and activity of soil methanotrophs, and the main cause could be the increase of soil moisture content.

Key words: temperate forest soil, elevated CO2 concentration, methane, methanotrophs