Impact of conversion of coastal wetlands into paddy fields on the process of nitrite-dependent anaerobic methane oxidation

n-damo activity increased by 43.6%-165.8% after conversion in mangrove wetland.n-damo activity showed no significant change after conversion in P. australis wetland.Community altered more significantly after conversion in mangrove wetland.Bulk density, salinity, and organic carbon were main factors affecting n-damo activity.Nitrite-dependent anaerobic methane oxidation (n-damo), performed by the bacteria associated with Candidatus Methylomirabilis oxyfera, acts as a novel methane sink in coastal wetlands. Conversion of coastal wetlands into paddy fields is a common land-use change that has profound effects on methane emissions, but its impact on n-damo process is nearly unknown. Our study adopted a space-for-time substitution method to compare n-damo activity and community of Methylomirabilis-like bacteria between natural vegetation covered by Phragmites australis, Kandelia candek, or Bruguiera sexangula and adjacent converted paddy fields in six China's coastal wetlands. Generalized linear mixed model indicated that the activity of n-damo significantly increased by 43.6% and 165.8% after conversion of K. candek and B. sexangula wetlands into rice paddies, respectively, while the activity exhibited no significant change after conversion of P. australis wetlands. Furthermore, the abundance of Methylomirabilis-like bacteria significantly increased by 90.2%, 210.0%, and 110.1% following the conversion in wetlands covered by K. candek, B. sexangula, and P. australis, respectively. Principal co-ordinates analysis revealed significant changes in community structure of Methylomirabilis-like bacteria among vegetation types, with K. candek and B. sexangula showing a greater divergence than P. australis when compared to respective paddy fields. Path analysis indicated that land conversion resulted in changes in soil moisture content, organic carbon content, bulk density, and salinity and further affected the abundance of Methylomirabilis-like bacteria and ultimately n-damo activity. Overall, this is the first study to reveal the impact of conversion of coastal wetlands into paddy fields on n-damo activity and Methylomirabilis-like bacteria, and the impact was closely associated with the original native plant types. The results can enhance our understanding of the microbial-driven mechanisms of the impact of land conversion on methane emissions.