Abstract: The effects of rice-fish coculture on soil methane (CH₄) emission have been well documented, but it remains unclear whether rice-fish coculture affects methanogens and methanotrophs. To examine the effects of rice-fish coculture on soil methanogens and methanotrophs, we conducted a field experiment in the site of the Globally Important Agricultural Heritage Systems (GIAHS)―Qingtian rice-fish system. There were three treatments, including rice monoculture (RM), rice-fish coculture without feed (RFN), and rice-fish coculture with feed (RFF). The yields of rice and fish, the contents of soil organic carbon (SOC), soil total nitrogen (TN) and soil total phosphorus (TP), and the communities of methanogens and methanotrophs were examined. The results showed that rice yield and the increments of SOC and TN in the treatment RFF were significantly higher than those in treatments RM and RFN. Quantitative PCR (qPCR) analysis showed that the abundances of methanogen and methanotroph in both RFN and RFF were significantly higher than those in RM, while RFF had significantly higher methanotroph abundance than RFN. The Illumina Miseq analyses showed that both RFN and RFF affected the community structure of methanogen, but did not affect the methanotroph. For the different metabolic types of methanogens, RFN and RFF had higher abundance of Hydrogenotrophic than RM, and RFF had higher abundance of Aceticlastic than RFN. For the different metabolic types of methanotrophs, both RFN and RFF did not affect the abundance of Type I compared to RM, but the abundance of Type Ⅱ in RFF was significantly higher than those in RM and RFN. Our results suggest that rice-fish coculture affects the community composition of methanogen and methanotroph, which may be mediated by fish feed input.

Key words: rice-fish coculture system, soil microorganisms, methanogen, methanotroph.