Lower‐than‐expected CH 4 emissions from rice paddies with rising CO 2 concentrations

Elevated atmospheric CO 2 (eCO 2 ) generally increases carbon input in rice paddy soils and stimulates the growth of methane‐producing microorganisms. Therefore, eCO 2 is widely expected to increase methane (CH 4 ) emissions from rice agriculture, a major source of anthropogenic CH 4 . Agricultural practices strongly affect CH 4 emissions from rice paddies as well, but whether these practices modulate effects of eCO 2 is unclear. Here we show, by combining a series of experiments and meta‐analyses, that whereas eCO 2 strongly increased CH 4 emissions from paddies without straw incorporation, it tended to reduce CH 4 emissions from paddy soils with straw incorporation. Our experiments also identified the microbial processes underlying these results: eCO 2 increased methane‐consuming microorganisms more strongly in soils with straw incorporation than in soils without straw, with the opposite pattern for methane‐producing microorganisms. Accounting for the interaction between CO 2 and straw management, we estimate that eCO 2 increases global CH 4 emissions from rice paddies by 3.7%, an order of magnitude lower than previous estimates. Our results suggest that the effect of eCO 2 on CH 4 emissions from rice paddies is smaller than previously thought and underline the need for judicious agricultural management to curb future CH 4 emissions.