Stimulation of nitrate-driven AOM potential in paddy soils under elevated atmospheric CO₂ concentration

Elevated atmospheric CO₂ concentrations have profound effects on methane (CH₄) emissions from rice paddies, yet their impact on anaerobic oxidation of methane (AOM) remains largely unexplored. This study aimed to explore how elevated CO₂ affects the nitrate-driven AOM potential and the abundance and community composition of the associated anaerobic methanotrophs in paddy fields across three soil depths (0-5, 5-10, and 10-20 cm) and three rice growth stages (tillering, jointing, and flowering) through a controlled field experiment using an open-top chamber (OTC) platform. The results showed that the elevated CO₂ (increase of 200 ppm above ambient concentration for 4 years) significantly enhanced nitrate-driven AOM potential, with an average increase of 52.5 % compared to ambient condition. This stimulation was closely associated with the increased dissolved organic carbon levels under CO₂ enrichment, showing a 22.7 % increase relative to ambient CO₂. Furthermore, Methanoperedens-like archaea exhibited an average increase in abundance of 32.1 % under elevated CO₂, but their community composition remained stable across different CO₂ treatments. In addition, nitrate-driven AOM potential varied significantly with soil depth and rice growth stages, with the highest potential being observed in surface soils (0-5 cm) and during the jointing stage. Overall, our findings demonstrated that elevated CO₂ concentrations greatly enhanced nitrate-driven AOM potential, highlighting the role of this AOM process as a potential key microbial CH₄ sink under future climate change scenarios.