Abstract
Abstract. The degradation of organic matter to CH4 and CO2 was investigated in three different boreal peatland systems in Finland, a mesotrophic fen (MES), an oligotrophic fen (OLI), and an ombrotrophic peat (OMB). MES had similar production rates of CO2 and CH4, but the two nutrient-poor peatlands (OLI and OMB) produced in general more CO2 than CH4. δ13C analysis of CH4 and CO2 in the presence and absence methyl fluoride (CH3F), an inhibitor of acetoclastic methanogenesis, showed that CH4 was predominantly produced by hydrogenotrophic methanogenesis and that acetoclastic methanogenesis only played an important role in MES. These results, together with our observations concerning the collective inhibition of CH4 and CO2 production rates by CH3F, indicate that organic matter was degraded through different paths in the mesotrophic and the nutrient-poor peatlands. In the mesotrophic fen, the major process is canonical fermentation followed by acetoclastic and hydrogenotrophic methanogenesis, while in the nutrient-poor peat, organic matter was apparently degraded to a large extent by a different path which finally involved hydrogenotrophic methanogenesis. Our data suggest that degradation of organic substances in the oligotrophic environments was incomplete and involved the use of organic compounds as oxidants.
Highlights
Northern peatlands cover about 400 million km2 (Gorham, 1991) and are important emitters of the greenhouse gas methane (Matthews and Fung, 1987; Bartlett and Harriss, 1993)
mesotrophic fen (MES) had similar production rates of CO2 and CH4, but the two nutrientpoor peatlands (OLI and ombrotrophic peat (OMB)) produced in general more CO2 than CH4. δ13C analysis of CH4 and CO2 in the presence and absence methyl fluoride (CH3F), an inhibitor of acetoclastic methanogenesis, showed that CH4 was predominantly produced by hydrogenotrophic methanogenesis and that acetoclastic methanogenesis only played an important role in MES
Production rates of CH4 were much higher in peat samples from the mesotrophic fen (MES) than from the ombrotrophic peat (OMB) and the oligotrophic fen (OLI) (Table 1)
Summary
Northern peatlands cover about 400 million km (Gorham, 1991) and are important emitters of the greenhouse gas methane (Matthews and Fung, 1987; Bartlett and Harriss, 1993). Degradation of cellulose, for example, would result in the production of 2 acetate, 2 CO2 and 4 H2 from each hexose molecule, which are further converted by acetoclastic and hydrogenotrophic methanogenesis to 3 CH4 and 3 CO2 (Conrad, 1999). Under these conditions, 2 CH4 are derived from acetate and 1 CH4 from H2/CO2. 2 CH4 are derived from acetate and 1 CH4 from H2/CO2 This path of CH4 production has been demonstrated in various peat bogs ranging from Michigan (Avery et al, 1999), western Siberia (Kotsyurbenko et al, 2004) to the permafrost region of northwestern Siberia (Metje and Frenzel, 2007). Later studies indicated that a decreasing pH resulted in decreasing acetate turnover and in the relative dominance of hydrogenotrophic methanogenesis (Kotsyurbenko et al, 2007), and that the type of vegetation, i.e., dominance of Sphagnum
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