Stable carbon isotope fractionation during methanogenesis in three boreal peatland ecosystems.

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. [ABSTRACT FROM AUTHOR]