Microbial Mechanisms Governing the Reduction of CH4 Emission in Coastal Wetlands under Elevated CO2 Conditions

Elevated levels of CO2 are known to enhance CH4 emissions from wetlands due to the combined effects of increased plant biomass and greater carbon availability for methanogens. However, recent findings have demonstrated a decrease in CH4 emissions under elevated CO2 conditions in coastal wetlands, primarily attributed to the oxygen priming effect. Despite this knowledge, direct evidence elucidating the microbial processes underlying this reduction remains elusive. In this study, we employed mRNA-based analysis to identify the active microorganisms responsible for CH4 dynamics. Under elevated CO2 conditions, we observed lower methanogen abundances compared to ambient CO2 levels, suggesting that the oxygen priming effect inhibited the activity of methane-producing microbes. Intriguingly, no significant differences were found for methanotrophs, whose impact on wetland sediments may be minimal. Additionally, there was no notable change in the abundance of dsrA genes, indicating that the reduction in CH4 emission was not a result of carbon substrate competition with sulfate reducers. This research contributes valuable insights into the microbial mechanisms governing CH4 emissions in coastal wetlands under elevated CO2 conditions.