[Effect of gradual increase of atmospheric CO concentration on nitrate-dependent anaerobic methane oxidation in paddy soils].

Nitrate-dependent anaerobic oxidation of methane (AOM) is a new pathway to reduce methane emissions from paddy ecosystems. The elevated atmospheric CO concentration can affect methane emissions from paddy ecosystems, but its impact on the process of nitrate-dependent AOM is poorly known. Based on the automatic CO control platform with open top chambers and the CH stable isotope experiments, the responses of the activity of nitrate-dependent AOM, abundance and community composition of Methanoperedens nitroreducens ()-like archaea to the gradual increase of CO concentration were investigated in paddy fields. We set up two CO concentration treatments, including an ambient CO and a gradual increase of CO(increase of 40 μL·L per year above ambient CO concentration until 160 μL·L). The results showed the nitrate-dependent AOM rate of 0.7-11.3 nmol CO·g·d in the studied paddy fields, and quantitative PCR showed the abundance of -like archaeal genes of 2.2×10-8.5×10 copies·g. Compared to the ambient CO treatment, the slow elevated CO treatment enhanced the nitrate-dependent AOM rate and stimulated the abundance of -like archaea, particularly in 5-10 cm soil layer. The gradual increased CO concentration treatment did not change the community composition of -like archaea, but significantly decreased their diversity. The soil organic carbon content was an important factor influencing the nitrate-dependent AOM process. Overall, our results showed that the gradual increase of CO concentration could promote the nitrate-dependent AOM, suggesting its positive role in mitigating methane emissions from paddy ecosystems under future climate change.