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Trophic links between fermentation and methanogenesis of soil derived from a methane-emitting, moderately acidic temperate fen (pH 4.5) were investigated. Initial CO2:CH4 production ratios in anoxic microcosms indicated that methanogenesis was concomitant to other terminal anaerobic processes. Methane production in anoxic microcosms atin situpH was stimulated by supplemental H2-CO2, formate or methanol; supplemental acetate did not stimulate methanogenesis. Supplemental H2-CO2, formate or methanol also stimulated the formation of acetate, indicating that the fen harbours moderately acid-tolerant acetogens. Supplemental monosaccharides (glucose,N-acetylglucosamine and xylose) stimulated the production of CO2, H2, acetate and other fermentation products when methanogenesis was inhibited with 2-bromoethane sulfonate 20 mM. Glucose stimulated methanogenesis in the absence of BES. Upper soil depths yielded higher anaerobic activities and also higher numbers of cells. Detected archaeal 16S rRNA genes were indicative of H2-CO2- and formate-consuming methanogens (Methanomicrobiaceae), obligate acetoclastic methanogens (Methanosaetaceae) and crenarchaeotes (groups I.1a, I.1c and I.3). Molecular analyses of partial sequences of 16S rRNA genes revealed the presence ofAcidobacteria, Nitrospirales, Clamydiales, Clostridiales, Alpha-, Gamma-, DeltaproteobacteriaandCyanobacteria.These collective results suggest that this moderately acidic fen harbours phylogenetically diverse, moderately acid tolerant fermenters (both facultative aerobes and obligate anaerobes) that are trophically linked to methanogenesis.