Conversion of coastal wetlands to paddy fields substantially decreases methane oxidation potential and methanotrophic abundance on the eastern coast of China.

Coastal wetland ecosystems play a key role in the global carbon cycle and climate mitigation. The land conversion of coastal wetlands to paddy fields, an increasingly common practice to feed the growing population, has been shown to dramatically stimulate the methane emissions of (CH). However, the knowledge about how such wetland conversion affects the methane oxidation, a key process regulating methane emissions from coastal wetlands, is nearly unknown. In this study, a space-for-time substitution method was employed to investigate the impact of the conversion of coastal wetlands (dominated by Phragmites or mangrove (Kandelia and Bruguiera)) to paddy fields on the methane oxidation process on the eastern coast of China. Our results showed that the average CH oxidation potential in the converted paddy soils significantly reduced by 28.4 % and 29.3 %, respectively, and the average abundance of methanotrophic pmoA gene decreased by 77.1 % and 81.9 %, respectively, compared to the original Phragmites and mangrove soils. Significant changes in the methanotrophic community composition were also found after converting Phragmites and mangrove wetlands to paddy fields. Structural equation modeling analysis suggested that the land conversion significantly affected the CH oxidation potential by changing the soil physicochemical properties (pH, ammonium content, and nitrate content) and methanotrophic abundance. Overall this study showed significant alterations in CH oxidation potential and community composition and abundance of methanotrophs caused by conversion of coastal wetlands to paddy fields, improving the knowledge of the underlying microbial mechanisms of land conversion on methane emissions.