Stimulation of methane production potential and alteration in community composition of methanogens following conversion of China’s coastal marshes to paddy fields

Conversion of coastal marshes to paddy fields can significantly affect methane (CH₄) emissions. However, how such land conversion impacts methanogenesis, a key microbial process regulating CH₄ emissions, is poorly known. This investigation adopted a space-for-time substitution method to compare soil methane production potential (MPP), abundance and community composition of methanogenic archaea between marsh land (covered by Kandelia candek, Phragmites australis, or Bruguiera sexangula) and nearby paddy fields in six different regions along the coast of China. Linear mixed-effects models showed that the conversion of salt marshes to paddy fields resulted in significant increases in overall MPP and abundance of methanogenic archaea by 343 % and 346 % in average, respectively. A significant variation in the community composition of methanogenic archaea was observed between marsh land and paddy fields, with the dominant genera shifting from Methanolobus (32.1 %) and Methanosarcina (27.3 %) to Methanobacterium (49.0 %). Partial least squares path model showed that the change of MPP was primarily driven by abundance of methanogenic archaea, and the abundance was affected by alterations in soil physicochemical properties (e.g., organic carbon content, NH₄⁺ content, and salinity) and community composition of methanogenic archaea caused by land conversion. Moreover, both MPP and abundance of methanogenic archaea were significantly correlated with the conversion years. Collectively, this study was the first to show the dynamic response of MPP and community of methanogenic archaea to the conversion of coastal marshes to paddy fields, thereby enhancing our understanding of land conversion’s impact on CH₄ cycling and the underlying mechanism.