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

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