Effects of Soil Microbes on Methane Emissions from Paddy Fields under Varying Soil Oxygen Conditions

Core Ideas Improvement in the soil oxygen condition reduced methane emissions from the paddy fields. Methane emissions exhibited two peaks (tillering and booting stage) during rice growth stage. Methane emissions in the paddy field were mainly concentrated prior to the full heading stage. Soil oxygen conditions and rice development stages both affected the diurnal variation of the CH4 fluxes. A two‐year experiment was conducted in southeast China to investigate the effects of microbes at different soil oxygen conditions, including continuous flooding (CF), chemical aeration (CA), and alternate wetting and drying (AWD) on methane (CH4) emissions from paddy fields. Two peaks of seasonal CH4 fluxes appeared at the tillering and booting stages and the first peak was higher than the second. The diurnal CH4 fluxes exhibited one peak during tillering stage and two peaks during booting stage in CF and CA treatments, whereas one peak was observed in AWD treatment. The CA and AWD treatments reduced CH4 emissions but increased rice yield than CF treatment in both years. Compared with CF treatment, the average flux in CA and AWD treatments was reduced by 31.75% and 49.89% in 2015 and by 28.25% and 41.97% in 2016, respectively. The CA and AWD treatments had higher soil redox potentials (Eh), larger methanotrophic pmoA copy numbers, lower soil dehydrogenase activity, lower methanogenic mcrA copy numbers, and lower soil microbial biomass C than CF treatment. Significant positive correlations were observed between the CH4 emissions and the abundance of methanogen, soil dehydrogenase activity, and soil respiration; significant negative correlations were observed between the CH4 emissions and the abundance of methanotrophs, and soil Eh. Our results indicate that an improvement in soil oxygen conditions decreased the abundance of methanogens, increased the abundance of methanotrophs, and improved Eh, thereby contributing to a reduction in the CH4 emissions without affecting rice yield.