| Summary: | Due to their role as CO2 sinks and CH4 sources peatlands have contributed fundamentally to the global carbon cycle. Especially peatlands of the northern hemisphere are important reservoirs for soil organic carbon. A global warming will make available these carbon reservoirs for microbial degradation and may stimulate CH4 and CO2 emissions. Physiology and thermodynamics of methanogenesis have been studied extensively. However, the linkage between structure and function of methanogenic communities and the regulatory factors in acidic peatlands are largely unresolved. Here, we studied methanogenic communities and processes coupled to methanogenesis in acidic peatlands of the northern hemisphere (N-Finland, W-Siberia and Estonia). In the first study the relevance of endogenic ethanol as substrate for methanogenesis and Fe(III) reduction in a subarctic peatland in Northern Finland was revealed. Carbon balances showed that 50% of the ethanol pool entered methanogenesis via syntrophic oxidation and 50% Fe(III) reduction. 80% of CH4 originated from H2/CO2. Correspondingly, phylogenetic analysis of the 16S rRNA gene and the gene for the α-subunit of the methyl coenzymeM reductase revealed that a single member of the family Methanobacteriaceae was responsible for methanogenesis. Relatively high methanogenesis even at 4°C indicated the presence of a psychrophilic community. T-RFLP analysis argued for stability of the archaeal community over the whole temperature gradient. However, Real Time PCR revealed a temperature dependent growth of both the bacterial and archaeal community. Both, substrate turnover and growth of the microbial community were strongly temperature dependent Similar to the Finnish peatland, syntrophic processes seemed to be main sources for methanogenic substrates in the Siberian peat as well. Inhibition of acetoclastic methanogenesis with CH3F revealed that >70% of CH4 originated from acetate. Based on the stochiometric ratio of acetate and H2/CO2 originating from syntrophic butyrate oxidation, this ...
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