Effects of continuous manure application on methanogenic and methanotrophic communities and methane production potentials in rice paddy soil

Livestock manures are broadly used in agriculture to improve soil productivity; however, the impact of continuous manure application on the behaviors of methanogens (mcrA) and methanotrophs (pmoA) is poorly understood. The objective of this study was to determine the influence of continuous pig manure application on methanogenic and methanotrophic communities and the methane production potentials (MPPs) of rice paddy soil. The results show that adding manure induced significantly higher mcrA gene abundance than chemical fertilizer treatments, and that manure led to higher mcrA gene abundance when it was applied together with full NPK fertilizers than it did when applied with N or NP fertilizers. However, there were no obvious effects of continuous manure application on pmoA gene abundance. The community structures of mcrA and pmoA were distinctly altered by continuous manure application, and their variation was closely associated with fertilizer-induced changes in dissolved organic C, total P, and available P and K in the soil. We also observed that manure application along with full NPK fertilizers caused significantly higher MPPs compared to chemical fertilization alone, while manure application with N or NP fertilizers had no obvious effect on MPPs. Moreover, MPPs were positively correlated with mcrA gene abundance, suggesting that continuous manure application may enhance methane emissions by stimulating methane production. Therefore, long-term manure application can affect both the abundance and composition of methanogens, and thus, enhance methane production. This effect is largely dependent on soil nutritional status.