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.