Winter drainage and film mulching cultivation mitigated CH emission by regulating the function and structure of methanogenic archaeal and fermenting bacterial communities in paddy soil.

Winter flooding of harvested rice fields is a typical cropping system in mountainous areas, which emits considerable amounts of CH. Plastic film mulching cultivation is recognized as an important rice cultivation practice in paddy field for water-saving irrigation. However, the effects of these managements on CH emissions in paddy soil and the underlying microbial mechanism are unclear. A field experiment was carried out with the application of winter drainage followed by traditional rice cultivation (WD), winter drainage followed by plastic film mulching cultivation (MC), as well as winter flooding followed by traditional rice cultivation (WF) as control in hilly paddy fields. We investigated the CH emissions, functional (CH production rate, C isotope) and structural (abundance, structure) responses of soil methanogenic archaeal and fermenting bacterial communities during rice season. Shifting the fields from WF into WD and MC substantially mitigated CH emissions by 62.3% and 59.2%, respectively, paralleled with the enhancement of soil Eh and the reductions of soil DOC content. Compared with WF, WD and MC both significantly decreased CH production rates and the copy numbers of mcrA gene. Moreover, an increasing contribution of hydrogenotrophic methanogenesis (from 30.7% to 50.0%) to total CH production was observed during the conversion from WF to MC under an anaerobic incubation, paralleled with the decreased acetate content and increased δC values of acetate-methyl and total acetate. The communities of methanogenic archaea and fermenting bacteria strongly responded to the shift from WF to WD, while MC only showed significant effects on the methanogenic archaeal communities. Compared with WF, WD and MC significantly increased the relative abundance of Methanothrix, Methanosarcina and Methanocella, while those of Methanoregula, Massilia and Geobacter were decreased. The co-occurrence networks showed that WD and MC induced the loss of mixed methanogenic fermentation modules, indicating the decrease in functional biodiversity and redundancy of fermenting bacterial and methanogenic archaeal communities.The findings suggest that WD and MC approach mitigate CH emission by regulating the function and structure of methanogenic archaeal and fermenting bacterial communities in paddy soil, which represent the effective management strategies considering the water availability and CH mitigation in paddy-field agriculture.