Methanogenic and methanotrophic communities determine lower CH₄ fluxes in a subtropical paddy field under long-term...

Clarifying the effects of elevated CO₂ concentration (e[CO₂]) on CH₄ emissions from paddy fields and its mechanisms is a crucial part of the research on agricultural systems in response to global climate change. However, the response of CH₄ fluxes from rice fields to long-term e[CO₂] (e[CO₂] duration >10 years) and its microbial mechanism is still lacking. In this study, we used a long-term free-air CO₂ enrichment experiment to examine the relationship between CH₄ fluxes and the methanogenic and methanotrophic consortia under long- and short-term e[CO₂]. We demonstrated that contrary to the effect of short-term e[CO₂], long-term e[CO₂] decreased CH₄ fluxes. This may be associated with the reduction of methanogenic abundance and the increase of methanotrophic abundance under long-term e[CO₂]. In addition, long-term e[CO₂] also changed the community structure and composition of methanogens and methanotrophs compared with short-term e[CO₂]. Partial least squares path modeling analysis showed that long-term e[CO₂] also could affect the abundance and composition of methanogens and methanotrophs indirectly by influencing soil physical and chemical properties, thereby ultimately altering CH₄ fluxes in paddy soils. These findings suggest that current estimates of short-term e[CO₂]-induced CH₄ fluxes from paddy fields may be overestimated. Therefore, a comprehensive assessment of climate‑carbon cycle feedbacks may need to consider the microbial regulation of CH₄ production and oxidation processes in paddy ecosystems under long-term e[CO₂].