Long-term incorporation of wheat straw changes the methane oxidation potential, abundance and community composition of methanotrophs in a paddy ecosystem

Abstract

A recent study showed that the Intergovernmental Panel on Climate Change (IPCC) methodologies overestimated the effect of long-term (>5 years) straw incorporation on CH4 emissions from paddy ecosystems. It was suggested that the IPCC methodologies underestimated the active role of methanotrophs in regulating CH4 emissions under long-term straw incorporation; however, direct evidence has not yet been provided. Herein, the methane oxidation potential, abundance and community composition of methanotrophs were investigated in paddy fields under three long-term (32 years) fertilization treatments, including unfertilized control (CK), mineral fertilizers (NPK), and wheat straw incorporation with mineral fertilizers (SNPK). The results showed that the methane oxidation potential in the SNPK treatment was significantly (p < 0.05) higher than those in the NPK and CK treatments. Furthermore, the pmoA gene abundance of methanotrophs was also significantly (p < 0.05) higher in the SNPK treatment than that in the NPK and CK treatments. It was calculated that the overall methane oxidation potential in the SNPK treatment was increased by 67.0% and 62.5% in comparison to the CK and NPK treatments, respectively. Similarly, the pmoA gene abundance in the SNPK treatment was increased by 87.1% and 59.1% as compared to other two treatments, respectively. In addition, the SNPK treatment significantly increased the relative abundance of type II methanotrophs (Methylocystis). The changes in soil organic carbon (OrgC) content, nitrate content, and aeration status under the SNPK treatment were the key factors affecting the methane oxidation potential and communities of methanotrophs. Taken together, we provide the first direct evidence that methanotrophs responded positively to long-term straw incorporation in paddy ecosystems, which could partly explain the overestimation by the IPCC methodologies of CH4 emissions induced due to straw incorporation.