Elevated [CO2] reduces CH4 emissions from rice paddies under in situ straw incorporation.

Rice paddies contribute to ∼48% of greenhouse gas emissions from cropland, with ∼94% from methane (CH 4). Elevated atmospheric CO 2 concentrations (eCO 2) due to human activities, generally stimulate the rice growth, and in turn affect CH 4 emissions from rice paddies. However, the effects of eCO 2 on CH 4 emissions from rice paddies are still unclear under in situ straw incorporation, the popular agricultural practice. Therefore, we conducted a 3-yr field experiment to investigate the effects of eCO 2 on CH 4 emissions under in situ straw incorporation in the rice-wheat cropping system, using the open-top chamber technology. We found that eCO 2 reduced the CH 4 emissions from rice paddies by 10.9–23.8%, but increased rice plant biomass by 4.2–35.6%. The eCO 2 reduced the soil NH 4 + and NO 3 - concentrations, but did not affect the soil dissolved organic C. The eCO 2 did not affect the abundance of methanogens and CH 4 production potential, whereas it stimulated the abundance of methanotrophs and CH 4 oxidation potential by 102.5% and 15.1%, respectively. The eCO 2 also shifted the community composition of methanotrophs and reduced the relative abundance of type Ⅱ methanotrophs by 8.5%. The random forest analysis identified that soil CH 4 oxidation potential is the most important factor affecting CH 4 emissions. Our findings indicate that eCO 2 can reduce the CH 4 emissions from rice paddies under in situ straw incorporation mainly through increasing the soil CH 4 oxidation potential. Our study suggests the effects of eCO 2 on CH 4 emissions from global paddies may be overestimated and underline the need for smart agricultural management to reduce CH 4 emissions. • Elevated CO 2 reduced CH 4 emission from paddies under in situ straw incorporation. • Elevated CO 2 stimulated abundance of methanotrophs and CH 4 oxidation potential. • Soil CH 4 oxidation potential is the most important factor affecting CH 4 emissions. [ABSTRACT FROM AUTHOR]