Manure Amendment Increased the Abundance of Methanogens and Methanotrophs but Suppressed the Type I Methanotrophs in Rice Paddies

Methane (CH) emission is the consequence of CH production and consumption performed by methanogens and methanotrophs, respectively. Fertilization is an important factor that regulates the behavior of methanogens and methanotrophs; however, the effect of manure and rice straw addition combined with inorganic fertilizers on these communities is not well understood. This study aimed to explore how manure and rice straw amendments together with inorganic fertilizers influenced the methanogenic and methanotrophic communities in a 31-year fertilized rice paddy. Manure amendment significantly increased the abundance of mcrA and pmoA genes by 61.2% and 63.3% compared with the unfertilized control, whereas inorganic NPK fertilization alone or rice straw addition did not affect their abundances. Manure and rice straw amendments greatly decreased the Shannon index and ACE index of the methanogenic communities, whereas inorganic NPK fertilization alone increased the ACE index of the methanotrophic communities compared with the unfertilized control. Methanosarcinaceae and Methylococcaceae dominated at the family level, representing 23.1-35.0% and 48.7-67.2% of the total reads, for the methanogenic and methanotrophic communities, respectively. Application of manure together with inorganic fertilizers suppressed the Methanocellales methanogens and the type I methanotrophs (Methylococcus and Methylobacter). Fertilization greatly altered the community structure of methanogens and methanotrophs, and manure addition had more apparent effects than rice straw. Moreover, total nitrogen, soil organic carbon, available phosphorus, and available potassium correlated significantly to the abundance, composition, and community structure of methanogens and methanotrophs. In conclusion, our study revealed that long-term manure amendment in combination with inorganic fertilizers significantly increased the abundance of methanogens and methanotrophs, but suppressed the type I methanotrophs in rice paddies.