Lower-than-expected CH emissions from rice paddies with rising CO concentrations.

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