Research progresses on methanogenesis pathway and methanogens in coastal wetlands

: Coastal wetlands contribute about 75% to the global oceanic CH4 emissions, thus play a vital role in global C cycles. In this paper, we provided a perspective on researches on metabolic, phylogenetic, and ecological diversity of the methanogenic archaea and the regulating environmental factors in coastal wetlands. Because of the presence of more favorable electron acceptors such as sulfate, methanogenesis via CO2 reduction and acetate fermentation are limited by availability of substrates, and hydrogenotrophic and acetotrophic methanogens generally express low relative abundance. In contrast, "non-competitive" substrates such as methanol and methylated compounds have been shown to contribute substantially to methane formation in coastal wetlands, and the facultative methanogens are predominant in those environments. Salinity regulates vegetation zonation and is related to SO42- concentration, by regulating types of methanogenic substrates and contents of compe-titive electron acceptors, indirectly affects the structure and function of methanogens. Major uncertainties in the current studies include the following: methanogen community structure, the key environmental factors regulating methane pathway, and their effects on methane emissions in coastal wetlands.