Methane Production in a West Siberian Eutrophic Fen Is Much Higher than Carbon Dioxide Production: Incubation of Peat Samples, Stoichiometry, Stable Isotope Dynamics, Modeling

Homoacetogenic bacteria can play an important role in anaerobic degradation of organic matter in peatlands at low temperatures. However, little is known about the conditions when they come on the scene. We carried out incubation experiments with peat samples from a West-Siberian eutrophic fen in the presence and absence of inhibitor sodium fluoroacetate (CH2FCOONa) and proposed the employment of dynamic modeling to clarify the contributions of different groups of bacteria and archaea to the degradation of organic matter to CH4 and CO2. At the end of experiments, CH4 content in the headspace was 2.6-3.1 times higher than that of CO2; pH values of peat solution were between 6.5 and 7.0. Dynamic modeling of CH4 and CO2 and their isotopic signatures showed that CH4 was predominantly produced through homoacetogenesis and acetoclastic methanogenesis, while hydrogenotrophic methanogenesis played a minor role in the process. Inhibitor addition led to a change in the pathway of methane formation to H-2-dependent methanogenesis. The comparatively large differences in the quantitative output of methane from different samples taken from the same field site were interpreted as a consequence of variation in the initial concentrations of biomass, cellulose, acetate, methane, and CO2. These differences also led to variations in the proportions of methane formed from acetate and H-2/CO2.