Methane Mitigation is Associated with Reduced Abundance of Methanogenic and Methanotrophic Communities in Paddy Soils Continuously Sub-irrigated with Treated Wastewater

Herein, we examined emissions of CH 4 and the community structures of methanogenic archaea and methanotrophic bacteria in paddy soils subjected to a novel irrigation system, namely continuous sub-irrigation with treated wastewater (TWW). This system has recently been developed by our group to effectively reuse TWW for the cultivation of protein-rich rice. The results showed that despite not using mineral fertilisers, the wastewater reuse system produced a high rice yield comparable to that of a conventional cultivation practice and reduced CH 4 emissions from paddy fields by 80%. During the reproductive stage of rice plants, when high levels of CH 4 emissions from both treatments were observed, continuous sub-irrigation with TWW not only considerably inhibited the growth of methanogens in the lower soil layer, but also vastly reduced the abundance of methanotrophs in the upper soil layer, which was strongly consistent with the effective mitigation of CH 4 . The compositions of the examined microbial communities were not particularly affected by the studied cultivation practices. Overall, this study demonstrated that continuous sub-irrigation with TWW was an effective method to produce high rice yield and simultaneously reduce CH 4 emissions from paddy fields, and it also highlighted the potential underlying microbial mechanisms of the greenhouse gas mitigation.