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Atmospheric CO 2 concentrations and water management practices both affect greenhouse gas (GHG) emissions from rice paddies, but interactive effects between these two factors are still unknown. Here, we show the first study to compare the impact of elevated atmospheric CO 2 (eCO 2) on GHG emissions under continuously flooded irrigation (CF) and under intermittently flooded (IF) conditions. Elevated CO 2 stimulated CH 4 emissions under CF by 50% in a field experiment and by 46% in a pot experiment, but it had no effect under IF in both experiments. Elevated CO 2 had no effect on N 2 O emissions in either the field or pot experiment. Rice root biomass, aboveground biomass and grain yield increased with eCO 2 , but were not affected by water management. Elevated CO 2 only stimulated the abundance of methanogens under CF, suggesting that increased soil O 2 availability with IF limited methanogenic activity under eCO 2. Our findings suggest that estimates of CH 4 emissions from global rice agriculture with eCO 2 need to account for recent changes in water management. • The first study to compare the effect of elevated CO 2 on GHG emissions under CF and IF. • Elevated CO 2 stimulated CH 4 emissions under CF, but had no effect under IF. • Elevated CO 2 did not affect N 2 O emissions under CF and IF. • Elevated CO 2 increased the abundance of methanogens under CF only. • Current estimates of CO 2 effects on CH 4 emissions from rice paddies may be too high. [ABSTRACT FROM AUTHOR]

Abstract: Increasing evidences have shown that dissolved organic components are responsible for the significant C and N exports from terrestrial ecosystems to the surrounding aquatic ecosystems and very sensitive to CO2 enrichment. However, there is still a lack of direct evidence about CO2-led effects on these components at the ecosystem scale, especially in wetlands. We, therefore, simultaneously investigated the contents of dissolved organic carbon (DOC) and dissolved nitrogen (DN) in the surface water and soil layer in a paddy field under FACE facility in Eastern China. Elevated CO2 significantly increased the contents of DOC and DN in the surface water by 18.0% and 14.3% on average. Elevated CO2 also increased DOC content in the soil, but decreased DN content. The contents of DOC and DN in the soil–water interface of 0–1cm soil layer were on average 22.4% and 47.5% higher than in the 5–15cm soil layer. Besides, significant higher DOC and DN contents existed in the soil porewater than in the surface water. Due to multiple drainage regime and rainstorm-induced runoffs in rice cropping regions, CO2-led DOC and DN increments in the surface water may increase C and N exports from paddies to the surrounding aquatic ecosystems under future climate patterns. [Copyright &y& Elsevier]