Control of methane metabolism in a forested northern wetland, New York State, by aeration, substrates, and peat size fractions

Although many northern peat-forming wetlands (peatlands) are a suitable habitat for anaerobic CH4-producing bacteria (methanogens), net CH4 fluxes are typically low in forested systems. We examined whether soil factors (aeration, substrate availability, peat size fractions) constrained net CH4 production in peat from a Sphagnum-moss dominated, forested peatland in central New York State. The mean rate of net CH4 production measured at 24degreesC was 79 nmol g(1) d(1), and the mean rate of CO2 production (respiration) was 5.7 mumol g(1) d(1), in surface (0 to 10 cm) and subsurface (30 to 40 cm) peat. Saturated peat (900% water content) exposed to oxic conditions for 2 days or 14 days showed no net CH4 production when subsequently exposed to anoxic conditions. Rates of CO2 production, measured concomitantly, were essentially the same under oxic and anoxic conditions, and net CH4 consumption under oxic conditions was barely affected by short-term exposure to anoxic conditions. Therefore, methanogens were particularly sensitive to aeration. Net CH4 production in whole peat increased within hours of adding either acetate, glucose, or ethanol, substrates that methanogens can convert directly or indirectly into CH4, indicating that availability of these substrate might limit net CH4 production in situ. In longer incubations of 30 days, only ethanol addition stimulated a large increase in net CH4 production, suggesting growth in the population of methanogens when ethanol was available. We fractionated peat into size fractions and the largest sized fraction (>1.19 mm), composed mostly of roots, showed the greatest net CH4 production, although net CH4 production in smaller fractions showed the largest response to ethanol addition. The circumstantial evidence presented here, that ethanol coming from plant roots supports net CH4 production in forested sites, merits more research.