Methane is a highly potent greenhouse gas that originates from both natural and anthropogenic origins. On a weight basis, methane is 21 times more efficient at trapping heat and warming the planet than carbon dioxide. Methane emissions from wetlands account for more than 75% of the global emissions from all natural sources. Methane is a highly reduced compound produced as the end product of anaerobic decomposition by a group of microorganisms called methanogens, which phylogenetically belong to Archaea. These strict anaerobes can utilize only a limited variety of substrates with H2-CO2 and acetate being the most important too. The H2-CO2 dependent methanogenesis is considered the dominant pathway of methane production in boreal peatlands. However, acetate-dependent methanogenesis sometimes dominates in fens. In rich fens, higher nutrient availability promotes the growth of vascular plants (primarily sedges). Roots of these vascular plants penetrate deep into the peat column and therefore transport potential carbon-rich substrates, such as acetate, into the anaerobic layer. Rapid decomposition of organic matter also provides abundant substrates for methanogens. Poor fens, with lower vascular plant cover than that of rich fens, generally have lower potentials for CH4, and a higher portion of the produced CH4 comes from H2-CO2. Similar to poor fens, Sphagnum-dominated bogs also have a higher proportion of CH4 produced from H2-CO2, and it may be that the dominance of mosses (without roots) and mycor-rhizal vascular plants (without deep carbon-rich roots), along with the reduced abundance of sedges with well-developed deep roots, prohibit movement of labile carbon substrates to the anaerobic peat layer. Low decomposition rates in acidic bogs also limit the amount of acetate that can be produced during peat decomposition, which in turn limits the acetoclastic pathway. Methanogen diversity in bogs is very low and the composition of the methanogen community in bogs also differs greatly from that characteristic of fens. In general, higher CH4 production is found in peatlands with higher vascular plant cover, and higher water tables are found in rich fens.
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