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Although many northern peat-forming wetlands (peatlands) are a suitable habitat for anaerobic CH[sub 4]-producing bacteria (methanogens), net CH[sub 4] fluxes are typically low in forested systems. We examined whether soil factors (aeration, substrate availability, peat size fractions) constrained net CH[sub 4] production in peat from a Sphagnum-moss dominated, forested peatland in central New York State. The mean rate of net CH[sub 4] production measured at 24° C was 79 nmol g[sup -1]d[sup -1], and the mean rate of CO[sub 2] production (respiration) was 5.7 μmol g[sup -1]d[sup -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 CH[sub 4] production when subsequently exposed to anoxic conditions. Rates of CO[sub 2] production, measured concomitantly, were essentially the same under oxic and anoxic conditions, and net CH[sub 4] consumption under oxic conditions was barely affected by short-term exposure to anoxic conditions. Therefore, methanogens were particularly sensitive to aeration. Net CH[sub 4] production in whole peat increased within hours of adding either acetate, glucose, or ethanol, substrates that methanogens can convert directly or indirectly into CH[sub 4], indicating that availability of these substrate might limit net CH[sub 4] production in situ. In longer incubations of 30 days, only ethanol addition stimulated a large increase in net CH[sub 4] 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 CH[sub 4] production, although net CH[sub 4] production in smaller fractions showed the largest response to ethanol addition. The circumstantial evidence presented here, that ethanol coming from plant roots supports net CH[sub 4] production in forested sites, merits more research. [ABSTRACT FROM AUTHOR]

We measured seasonal patterns in the fluxes of CH4 and CO2 in a forested wetland in central New York State from 1992 to 1995. The site was a red maple-hemlock swamp with permanent pools (~30cm deep), except when the pools dried during severe drought in 1995. Annual CH4 emissions from the pools to the atmosphere averaged 4.3 (+/- 2.4) mol m-2 during 1993 to 1995 and ranged from 1.9 mol m-2 in 1993 to 6.7 mol m-2 in 1995. CO2 emissions from the pools during 1993 and 1994 were 10.5 and 11.9 mol m-2, accounting for 84.6% and 75.6% of the gaseous carbon export during 1993 and 1994, respectively. A combination of temperature and carbon availability influenced seasonal CH4 and CO2 fluxes more than other environmental factors (temperature, water column depth, O2, CH4, dissolved organic carbon, NH4+, or dissolved inorganic carbon). Based on an observed 12 C threshold temperature, linear regression models explained from 31% to 77% of seasonal gas flux variability. Compared with other forested wetlands, this site produced substantially greater CH4 fluxes, and the CH4 flux accounted for a greater proportion of the total carbon flux from the system. [ABSTRACT FROM AUTHOR]

Peatlands are important players in climate change-biosphere feedbacks via long-term net carbon (C) accumulation in soil organic matter and as potential net C sources including the potent greenhouse gas methane (CH 4 ). Interactions of climate, site-hydrology, plant community, and groundwater chemical factors influence peatland development and functioning, including C dioxide (CO 2 ) and CH 4 fluxes, but the role of microbial community composition is not well understood. To assess microbial functional and taxonomic dissimilarities, we used high throughput sequencing of the small subunit ribosomal DNA (SSU rDNA) to determine bacterial and archaeal community composition in soils from twenty North American peatlands. Targeted DNA metabarcoding showed that although Proteobacteria, Acidobacteria, and Actinobacteria were the dominant phyla on average, intermediate and rich fens hosted greater diversity and taxonomic richness, as well as an array of candidate phyla when compared with acidic and nutrient-poor poor fens and bogs. Moreover, pH was revealed to be the strongest predictor of microbial community structure across sites. Predictive metagenome content (PICRUSt) showed increases in specific genes, such as purine/pyrimidine and amino-acid metabolism in mid-latitude peatlands from 38 to 45° N, suggesting a shift toward utilization of microbial biomass over utilization of initial plant biomass in these microbial communities. Overall, there appears to be noticeable differences in community structure between peatland classes, as well as differences in microbial metabolic activity between latitudes. These findings are in line with a predicted increase in the decomposition and accelerated C turnover, and suggest that peatlands north of 37° latitude may be particularly vulnerable to climate change.