The process of methanogenesis in paddy fields under different elevated CO2 concentrations

Abstract

Understanding the process of methanogenesis in paddy fields under the scenarios of future climate change is of great significance for reducing greenhouse gas emissions and regulating the soil carbon cycle. Methyl Coenzyme M Reductase subunit A (mcrA) of methanogens is a rate-limiting enzyme that catalyzes the final step of CH4 production. However, the mechanism of methanogenesis change in the paddy fields under different elevated CO2 concentrations (e[CO2]) is rarely explored in earlier studies. In this research, we explored how the methanogens affect CH4 flux in paddy fields under various (e[CO2]). CH4 flux and CH4 production potential (MPP), and mcrA gene abundance were quantitatively analyzed under C (ambient CO2 concentration), C1 (C + 160 ppm CO2), and C2 (C + 200 ppm CO2) treatments. Additionally, the community composition and structure of methanogens were also compared with Illumina MiSeq sequencing. The results showed that C2 treatment significantly increased CH4 flux and MPP at the tillering stage. E[CO2] had a positive effect on the abundance of methanogens, but the effect was insignificant. We detected four known dominant orders of methanogenesis in this study, such as Methanosarcinales, Methanobacteriales, Methanocellales, and Methanomicrobiales. Although e[CO2] did not significantly change the overall community structure and diversity of methanogens, C2 treatment significantly reduced the relative abundance of two uncultured genera compared to C treatment. A linear regression model of DOC, methanogenic abundance, and MPP can explain 67.2% of the variation of CH4 flux under e[CO2]. Overall, our results demonstrated that CH4 flux in paddy fields under e[CO2] was mainly controlled by soil unstable C substrate and the abundance and activity of methanogens in rhizosphere soil.