Elevated CO2 and goethite inhibited anaerobic oxidation of methane in paddy soils

Microbially mediated anaerobic oxidation of methane (AOM) regulates methane (CH4) fluxes. Increases in the global atmospheric carbon dioxide (CO2) concentration and iron oxide rich in paddy soils influence AOM. However, the response and mechanisms between these two processes and AOM remain unclear. Here, we investigated the coupling of elevated atmospheric CO2 concentrations (ambient CO2 + 200 ppm) and goethite with AOM via 13CH4 isotope tracer techniques and explored the dynamics of bacterial and archaeal communities by high-throughput sequencing. The coupling of 13CH4 with electron acceptors generates 13CO2, and its enrichment was used to evaluate CH4 oxidation. The results showed that elevated atmospheric CO2 and the addition of goethite resulted in a significant decrease of 13CO2 value produced from 13CH4 oxidation, thereby inhibiting CH4 oxidation. In addition, both elevated atmospheric CO2 and goethite addition increased the Richness, Shannon, and ACE indices of bacteria to varying degrees, whereas the diversity of archaea exhibited the opposite pattern. Additionally, the microbial community composition was significantly altered. Overall, the negative response of elevated atmospheric CO2 and goethite to AOM may guide CH4 emissions reduction from paddy soils under global warming and climate change, as well as the formulation of environmental policies such as carbon budgets for farmland.