Crosstalk between methanogens and methanotrophs determines methane emissions in a rice paddy under different watering regimes

Uncovering the environmental drivers and revealing the balance between methanogenesis and methanotrophy under different watering regimes are vital for understanding methane (CH4) emissions in rice paddies. Although the mechanisms and impacts of watering regimes on plant community structures in rice paddies have been intensively investigated, the methanogenic and methanotrophic reactions under drying stress that regulate CH4 emissions remain unclear. Here, we examined the watering regimes of rice fields to elucidate how continuous flooding and dry cultivation impacted and regulated CH4 emissions. Water-saving regimes (dry cultivation) significantly decreased CH4 emissions (70-90 %) compared to the flooding treatment. The methanogenic and methanotrophic abundance, composition and structures were stable under the two watering regimes, while microbial interactions demonstrated that the dry cultivation had fewer positive links to methanogens in contrast to flooding. Furthermore, the more positive links to methanotrophs and limited electron transfer within rice plant communities under dry cultivation were observed, which subsequently restricted methanogenesis, translating to lower CH4 emissions. Dry cultivation also weakened the correlations between environmental factors and methanogens, albeit strengthened the links to methanotrophs. Flooding treatment exhibited significantly positive electrical conductivity and dissolved organic carbon-methanogen correlations, which might have explained the higher CH4 emissions than the dry cultivation. These findings suggested that drying treatment reduced microbial connectivity and abundance of methanogenic drivers in the microbial network, which decreased the CH4 emissions compared with flooding treatment.