Pathways for methanogenesis and diversity of methanogenic archaea in three boreal peatland ecosystems

The main objectives of this study were to uncover the pathways used for methanogenesis in three different boreal peatland ecosystems and to describe the methanogenic populations involved. The mesotrophic fen had the lowest proportion of CH4 produced from H2-CO2. The oligotrophic fen was the most hydrogenotrophic, followed by the ombrotrophic bog. Each site was characterized by a specific group of methanogenic sequences belonging to Methanosaeta spp. (mesotrophic fen), rice cluster-I (oligotrophic fen), and fen cluster (ombrotrophic bog).     

Effects of short- and long-term water-level drawdown on the populations and activity of aerobic decomposers in a boreal peatland

We analysed the response of microbial communities, characterized by phospholipid fatty acids (PLFAs), to changing hydrological conditions at sites with different nutrient levels in a southern boreal peatland. Although PLFAs of Gram‐negative bacteria were characteristic of the peatland complex, microbial communities differed among sites (ombrotrophic bog, oligotrophic fen, mesotrophic fen) and sampling depths (0–5, 5–10, 10–20, 20–30 cm). The microbial communities in each site changed significantly following water‐level drawdown. The patterns of change varied among sites and sampling depths. The relative proportion of Gram‐negative bacteria decreased in the upper 10 cm but increased in deeper layers of the fen sites. Fungi benefited from water‐level drawdown in the upper 5 cm of the mesotrophic fen, but suffered in the drier surfaces of the ombrotrophic bog, especially in the 5–10 cm layer. In contrast, actinobacteria suffered from water‐level drawdown in the mesotrophic fen, but benefited in the drier surfaces of the ombrotrophic bog. Basal respiration rate correlated positively with pH and fungal PLFA, and negatively with depth. We suggest that the changes in microbial community structure after persistent water‐level drawdown follow not only the hydrological conditions but also the patterns of vegetation change. Our results imply that changes in structure and activity of the microbial community in response to climate change will be strongly dependent on the type of peatland.     

Methanogen communities and Bacteria along an ecohydrological gradient in a northern raised bog complex

Mires forming an ecohydrological gradient from nutrient-rich, groundwater-fed mesotrophic and oligotrophic fens to a nutrient-poor ombrotrophic bog were studied by comparing potential methane (CH(4)) production and methanogenic microbial communities. Methane production was measured from different depths of anoxic peat and methanogen communities were detected by detailed restriction fragment length polymorphism (RFLP) analysis of clone libraries, sequencing and phylogenetic analysis. Potential CH(4) production changed along the ecohydrological gradient with the fens displaying much higher production than the ombrotrophic bog. Methanogen diversity also decreased along the gradient. The two fens had very similar diversity of methanogenic methyl-coenzyme M reductase gene (mcrA), but in the upper layer of the bog the methanogen diversity was strikingly lower, and only one type of mcrA sequence was retrieved. It was related to the Fen cluster, a group of novel methanogenic sequences found earlier in Finnish mires. Bacterial 16S rDNA sequences from the fens fell into at least nine phyla, but only four phyla were retrieved from the bog. The most common bacterial groups were Deltaproteobacteria, Verrucomicrobia and Acidobacteria.     

Functional-Structural Analysis of Nitrogen-Cycle Bacteria in a Hypersaline Mat from the Omani Desert

Anaerobic microbial activity in northern peat soils most often results in more carbon dioxide (CO ₂ ) production than methane (CH₄) production. This study examined why methanogenic conditions (i.e., equal molar amounts of CH₄ production and CO₂ production) prevail so infrequently. We used peat soils from two ombrotrophic bogs and from two rheotrophic fens. The former two represented a relatively dry bog hummock and a wet bog hollow, and the latter two represented a forested fen and a sedge-dominated fen. We quantified gas production rates in soil samples incubated in vitro with and without added metabolic substrates (glucose, ethanol, H₂/CO₂). None of the peat soils exhibited methanogenic conditions when incubated in vitro for a short time (< 5 days) and without added substrates. Incubating some samples > 50 days without added substrates led to methanogenic conditions in only one of four experiments. The anaerobic CO₂:CH₄ production ratio ranged from 5:1 to 40:1 in peat soil without additions and was larger in samples from the dry bog hummock and forested fen than the wet bog hollow and sedge fen. Adding ethanol or glucose separately to peat soils led to methanogenic conditions within 5 days after the addition by stimulating rates of CH₄ production, suggesting CH₄ production from both hydrogenotrophic and acetoclastic methanogenesis. Our results suggest that methanogenic conditions in peat soils rely on a constant supply of easily decomposable metabolic substrates. Sample handling and incubation procedures might obscure methanogenic conditions in peat soil incubated in vitro.     

Methane-Oxidizing Bacteria in a Finnish Raised Mire Complex: Effects of Site Fertility and Drainage

Methane-oxidizing bacteria (MOB) are the only biological sinks for methane (CH₄). Drainage of peatlands is known to decrease overall CH₄ emission, but the effect on MOB is unknown. The objective of this work was to characterize the MOB community and activity in two ecohydrologically different pristine peatland ecosystems, a fen and a bog, and their counterparts that were drained in 1961. Oligotrophic fens are groundwater-fed peatlands, but ombrotrophic bogs receive additional water and nutrients only from rainwater. The sites were sampled in August 2003 down to 10 cm below the water table (WT), and cores were divided into 10-cm subsamples. CH₄ oxidation was measured by gas chromatography (GC) to characterize MOB activity. The MOB community structure was characterized by polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) and sequencing methods using partial pmoA and mmoX genes. The highest CH₄ oxidation rates were measured from the subsamples 20–30 and 30–40 cm above WT at the pristine oligotrophic fen (12.7 and 10.5 μmol CH₄ dm⁻³ h⁻¹, respectively), but the rates decreased to almost zero in the vicinity of WT. In the pristine ombrotrophic bog, the highest oxidation rate at 0–10 cm was lower than in the fen (8.10 μmol CH₄ dm⁻³ h⁻¹), but in contrast to the fen, oxidation rates of 4.5 μmol CH₄ dm⁻³ h⁻¹ were observed at WT and 10 cm below WT. Drainage reduced the CH₄ oxidation rates to maximum values of 1.67 and 5.77 μmol CH₄ dm⁻³ h⁻¹ at 30–40 and 20–30 cm of the fen and bog site, respectively. From the total of 13 pmoA-derived DGGE bands found in the study, 11, 3, 6, and 2 were observed in the pristine fen and bog and their drained counterparts, respectively. According to the nonmetric multidimensional scaling of the DGGE banding pattern, the MOB community of the pristine fen differed from the other sites. The majority of partial pmoA sequences belonged to type I MOB, whereas the partial mmoX bands that were observed only in the bog sites formed a distinct group relating more to type II MOB. This study indicates that fen and bog ecosystems differ in MOB activity and community structure, and both these factors are affected by drainage.     

Potential Hg methylation and MeHg demethylation rates related to the nutrient status of different boreal wetlands

Despite methylmercury (MeHg) production in boreal wetlands being a research focus for decades, little is known about factors in control of methylation and demethylation rates and the effect of wetland type. This is the first study reporting potential Hg methylation (k _m ) and MeHg demethylation rate constants (k _d ) in boreal wetland soils. Seven wetlands situated in northern and southern Sweden were characterized by climatic parameters, nutrient status (e.g. type of vegetation, pH, C/N ratio, specific UV-absorption), iron and sulfur biogeochemistry. Based on nutrient status, the wetlands were divided into three groups; (I) three northern, nutrient poor fens, (II) a nutrient gradient ranging from an ombrotrophic bog to a fen with intermediate nutrient status, and (III) southern, more nutrient rich sites including two mesotrophic wetlands and one alder (Alnus) forest swamp. The k _m /k _d ratio in general followed %MeHg in soil and both measures were highest at the fen site with intermediate nutrient status. Northern nutrient poor fens and the ombrotrophic bog showed intermediate values of %MeHg and k _m /k _d . The two mesotrophic wetlands showed the lowest %MeHg and k _m /k _d , whereas the alder swamp had high k _m and k _d , resulting in an intermediate k _m /k _d and %MeHg. Molybdate addition experiments suggest that net MeHg production was mainly caused by the activity of sulfate reducing bacteria. A comparison with other studies, show that k _m and %MeHg in boreal freshwater wetlands in general are higher than in other environments. Our results support previous suggestions that the highest MeHg net production in boreal landscapes is to be found in fens with an intermediate nutrient status.     

Effects of short-term drying and irrigation on CO2 and CH4 production and emission from mesocosms of a northern bog and an alpine fen

Atmospheric CO₂ and CH₄ exchange in peatlands is controlled by water table levels and soil moisture, but impacts of short periods of dryness and rainfall are poorly known. We conducted drying-rewetting experiments with mesocosms from an ombrotrophic northern bog and an alpine, minerotrophic fen. Efflux of CO₂ and CH₄ was measured using static chambers and turnover and diffusion rates were calculated from depth profiles of gas concentrations. Due to a much lower macroporosity in the fen compared to the bog peat, water table fluctuated more strongly when irrigation was stopped and resumed, about 11 cm in the fen and 5 cm in the bog peat. Small changes in air filled porosity caused CO₂ and CH₄ concentrations in the fen peat to be insensitive to changes in water table position. CO₂ emission was by a factor of 5 higher in the fen than in the bog mesocosms and changed little with water table position in both peats. This was probably caused by the importance of the uppermost, permanently unsaturated zone for auto- and heterotrophic CO₂ production, and a decoupling of air filled porosity from water table position. CH₄ emission was <0.4 mmol m^?2 day^?1 in the bog peat, and up to >12.6 mmol m^?2 day^?1 in the fen peat, where it was lowered by water table fluctuations. CH₄ production was limited to the saturated zone in the bog peat but proceeded in the capillary fringe of the fen peat. Water table drawdown partly led to inhibition of methanogenesis in the newly unsaturated zone, but CH₄ production appeared to continue after irrigation without time-lag. The identified effects of irrigation on soil moisture and respiration highlight the importance of peat physical properties for respiratory dynamics; but the atmospheric carbon exchange was fairly insensitive to the small-scale fluctuations induced.     

Ecoenzymatic stoichiometry and microbial processing of organic matter in northern bogs and fens reveals a common P-limitation between peatland types

We compared carbon (C), nitrogen (N), and phosphorus (P) concentrations in atmospheric deposition, runoff, and soils with microbial respiration [dehydrogenase (DHA)] and ecoenzyme activity (EEA) in an ombrotrophic bog and a minerotrophic fen to investigate the environmental drivers of biogeochemical cycling in peatlands at the Marcell Experimental Forest in northern Minnesota, USA. Ecoenzymatic stoichiometry was used to construct models for C use efficiency (CUE) and decomposition (M), and these were used to model respiration (R_m). Our goals were to determine the relative C, N, and P limitations on microbial processes and organic matter decomposition, and to identify environmental constraints on ecoenzymatic processes. Mean annual water, C, and P yields were greater in the fen, while N yields were similar in both the bog and fen. Soil chemistry differed between the bog and fen, and both watersheds exhibited significant differences among soil horizons. DHA and EEA differed by watersheds and soil horizons, CUE, M, and R_m differed only by soil horizons. C, N, or P limitations indicated by EEA stoichiometry were confirmed with orthogonal regressions of ecoenzyme pairs and enzyme vector analyses, and indicated greater N and P limitation in the bog than in the fen, with an overall tendency toward P-limitation in both the bog and fen. Ecoenzymatic stoichiometry, microbial respiration, and organic matter decomposition were responsive to resource availability and the environmental drivers of microbial metabolism, including those related to global climate changes.     

Growing season carbon gas exchange from peatlands used as a source of vegetation donor material for restoration

The moss layer transfer technique removes the top layer of vegetation from donor sites as a method to transfer propagules and restore degraded or reclaimed peatlands. As this technique is new, little is known about the impacts of moss layer transfer on vegetation and carbon fluxes following harvest. We monitored growing season carbon dioxide (CO₂) and methane (CH₄) fluxes as well as plant communities at donor sites and neighbouring natural peatland sites in an ombrotrophic bog and minerotrophic fen in Alberta, Canada from which material was harvested between 1 and 6 years prior to the study. Plant recovery at all donor sites was rapid with an average of 72% total plant cover one growing season after harvest at the fen and an average of 87% total plant cover two growing seasons after harvest at the bog. Moss cover also returned, averaging 84% 6 years after harvest at the bog. The majority of natural peatlands in western Canada are treed and tree recruitment at the donor sites was limited. Methane emissions were higher from donor sites compared to natural sites due to the high water table and greater sedge cover. Carbon budgets suggested that the donor fen and bog sites released higher CO₂ and CH₄ over the growing season compared to adjacent natural sites. However, vegetation re-establishment on donor sites was rapid, and it is possible that these sites will return to their original carbon-cycle functioning after disturbance, suggesting that donor sites may recover naturally without implementing management strategies.     

Change in fluxes of carbon dioxide,methane and nitrous oxide due to forest drainage of mire sites of different trophy

Northern peatlands accumulate atmospheric CO₂ thus counteracting climate warming. However, CH₄ which is more efficient as a greenhouse gas than CO₂, is produced in the anaerobic decomposition processes in peat. When peatlands are taken for forestry their water table is lowered by ditching. We studied long-term effects of lowered water table on the development of vegetation and the annual emissions of CO₂, CH₄ and N₂O in an ombrotrophic bog and in a minerotrophic fen in Finland. Reclamation of the peat sites for forestry had changed the composition and coverage of the field and ground layer species, and increased highly the growth of tree stand at the drained fen. In general, drainage increased the annual CO₂ emissions but the emissions were also affected by the natural fluctuations of water table. In contrast to CO₂, drainage had decreased the emissions of CH₄, the drained fen even consumed atmospheric CH₄. CO₂ and CH₄ emissions were higher in the virgin fen than in the virgin bog. There were no N₂O emissions from neither type of virgin sites. Drainage had, however, highly increased the N₂O emissions from the fen. The results suggest that post-drainage changes in gas fluxes depend on the trophy of the original mires.     

Climate change effects on carbon and nitrogen mineralization in peatlands through changes in soil quality

Climate change will directly affect carbon and nitrogen mineralization through changes in temperature and soil moisture, but it may also indirectly affect mineralization rates through changes in soil quality. We used an experimental mesocosm system to examine the effects of 6‐year manipulations of infrared loading (warming) and water‐table level on the potential anaerobic nitrogen and carbon (as carbon dioxide (CO₂) and methane (CH₄) production) mineralization potentials of bog and fen peat over 11 weeks under uniform anaerobic conditions. To investigate the response of the dominant methanogenic pathways, we also analyzed the stable isotope composition of CH₄ produced in the samples. Bog peat from the highest water‐table treatment produced more CO₂ than bog peat from drier mesocosms. Fen peat from the highest water‐table treatment produced the most CH₄. Cumulative nitrogen mineralization was lowest in bog peat from the warmest treatment and lowest in the fen peat from the highest water‐table treatment. As all samples were incubated under constant conditions, observed differences in mineralization patterns reflect changes in soil quality in response to climate treatments. The largest treatment effects on carbon mineralization as CO₂ occurred early in the incubations and were ameliorated over time, suggesting that the climate treatments changed the size and/or quality of a small labile carbon pool. CH₄ from the fen peat appeared to be predominately from the acetoclastic pathway, while in the bog peat a strong CH₄ oxidation signal was present despite the anaerobic conditions of our incubations. There was no evidence that changes in soil quality have lead to differences in the dominant methanogenic pathways in these systems. Overall, our results suggest that even relatively short‐term changes in climate can alter the quality of peat in bogs and fens, which could alter the response of peatland carbon and nitrogen mineralization to future climate change.     

Phylogenetic Comparison of the Methanogenic Communities from an Acidic, Oligotrophic Fen and an Anaerobic Digester Treating Municipal Wastewater Sludge

Methanogens play a critical role in the decomposition of organics under anaerobic conditions. The methanogenic consortia in saturated wetland soils are often subjected to large temperature fluctuations and acidic conditions, imposing a selective pressure for psychro- and acidotolerant community members; however, methanogenic communities in engineered digesters are frequently maintained within a narrow range of mesophilic and circumneutral conditions to retain system stability. To investigate the hypothesis that these two disparate environments have distinct methanogenic communities, the methanogens in an oligotrophic acidic fen and a mesophilic anaerobic digester treating municipal wastewater sludge were characterized by creating clone libraries for the 16S rRNA and methyl coenzyme M reductase alpha subunit (mcrA) genes. A quantitative framework was developed to assess the differences between these two communities by calculating the average sequence similarity for 16S rRNA genes and mcrA within a genus and family using sequences of isolated and characterized methanogens within the approved methanogen taxonomy. The average sequence similarities for 16S rRNA genes within a genus and family were 96.0 and 93.5%, respectively, and the average sequence similarities for mcrA within a genus and family were 88.9 and 79%, respectively. The clone libraries of the bog and digester environments showed no overlap at the species level and almost no overlap at the family level. Both libraries were dominated by clones related to uncultured methanogen groups within the Methanomicrobiales, although members of the Methanosarcinales and Methanobacteriales were also found in both libraries. Diversity indices for the 16S rRNA gene library of the bog and both mcrA libraries were similar, but these indices indicated much lower diversity in the 16S digester library than in the other three libraries.     

Cranefly (Diptera: Tipuloidea) fauna of a boreal mire system in relation to mire trophic status: implications for conservation and bioassessment

Craneflies (Diptera Tipuloidea) are a typical but poorly known insect group in various moist environments, such as mires. The area of natural mires has strongly decreased in Finland, and there is an urgent need to study and describe the fauna of mires and to determine whether different mire categories support different assemblages of craneflies that might have indicator value. Craneflies were studied using Malaise traps in the Kauhaneva mire system in minerotrophic and ombrotrophic sites, the former subdivided into meso- and oligotrophic sites. A total of 29 cranefly species were recorded. Species richness was highest in mesotrophic sites while the number of species was equally low in oligo- and ombrotrophic sites. Phylidorea squalens, Erioptera flavata, Pedicia rivosa and Tricyphona immaculata were identified as indicators for mesotrophic sites, but no indicators were found for oligo- or ombrotrophic sites. No differences between the species composition of minerotrophic (meso- and oligotrophic combined) and ombrotrophic sites were detected, but when three classes of trophic status were compared, a statistical difference was found. Cranefly species richness in Kauhaneva was low compared to pristine spring habitats. Our results imply, that a focus towards conservation and restoration of mire types with high trophic status would benefit also the conservation of cranefly diversity in the boreal ecoregion. Bioassesments and ecological surveys of craneflies should be designed to cover adequately all trophic status classes within a mire, and especially the mire types with highest trophic status. We also review the distribution and ecology of some potentially regionally threatened cranefly species.     

Nutrient limitation and morphological plasticity of the carnivorous pitcher plant Sarracenia purpurea in contrasting wetland environments

* Plasticity of leaf nutrient content and morphology, and macronutrient limitation were examined in the northern pitcher plant, Sarracenia purpurea subsp. purpurea, in relation to soil nutrient availability in an open, neutral pH fen and a shady, acidic ombrotrophic bog, over 2 yr following reciprocal transplantation of S. purpurea between the wetlands. * In both wetlands, plants were limited by nitrogen (N) but not phosphorus (P) (N content < 2% DW(-1), N : P < 14) but photosynthetic quantum yields were high (F(V)/F(M) > 0.79). Despite carnivory, leaf N content correlated with dissolved N availability to plant roots (leaf N vs , r(2) = 0.344, P < 0.0001); carnivorous N acquisition did not apparently overcome N limitation. * Following transplantation, N content and leaf morphological traits changed in new leaves to become more similar to plants in the new environment, reflecting wetland nutrient availability. Changes in leaf morphology were faster when plants were transplanted from fen to bog than from bog to fen, possibly reflecting a more stressful environment in the bog. * Morphological plasticity observed in response to changes in nutrient supply to the roots in natural habitats complements previous observations of morphological changes with experimental nutrient addition to pitchers.     

Effects of hydrologic changes on aboveground production and surface water chemistry in two boreal peatlands in Alberta: Implications for global warming

Aboveground net primary production (NPP) and surface water chemistryvariables were monitored in a lacustrine sedge fen and a bog for four years.There were no significant differences in precipitation, mean growing seasonannual temperature, and number of growing degree days from 1991 to 1994. Themean annual water levels in the lacustrine sedge fen differed significantly,whereas they were similar in the bog during these four years. We measured 15surface water variables in the lacustrine sedge fen and the bog, and foundthat only two correlated significantly with water level fluctuations. In thelacustrine sedge fen, calcium correlated positively (r²= 0.56) and nitrate correlated negatively (r² =0.20) with water levels. In the bog, potassium correlated positively(r² = 0.88) and total dissolved phosphorus correlatednegatively (r² = 0.62) with water levels. The remainingchemical variables showed no significant correlations with water levelfluctuations. Net primary production of the different vegetation strataappeared to respond to different environmental variables. In the lacustrinesedge fen, graminoid production was explained to a significant degree bywater levels (r² = 0.53), whereas shrub production wasexplained to a significant degree by surface water chemistry variables, suchas nitrate (r² = 0.74) and total phosphorus(r² = 0.22). In the bog, temperature was the onlyvariable that explained moss production to a significant degree(r² = 0.71), whereas ammonium explained graminoidproduction (r² = 0.66) and soluble reactive phosphorusexplained shrub production to significant degrees (r² =0.71). There are few direct data on the impact of climatic warming in borealwetlands, although paleoecological and 2×CO₂ model datahave provided some indications of past and possibly future changes invegetation composition, respectively. Our results suggest that thelacustrine sedge fen may succeed to a bog dominated by Sphagnum spp. andPicea mariana, whereas the bog may succeed to an upland-type forestecosystem. This revised version was published online in July 2006 with corrections to the Cover Date.     

Methane Biogeochemistry and Methanogen Communities in Two Northern Peatland Ecosystems,New York State

Rates of methane (CH₄) production vary considerably among northern peat-forming wetlands, and it is not clear whether variability is caused by environmental factors affecting CH₄ production or differences in methanogen communities. We investigated CH₄ production and emission dynamics concomitantly with 16S rRNA gene sequence-based community analysis of Archaea in two contrasting peat-forming northern wetlands, an ombrotrophic bog and a minerotrophic conifer swamp. Individual measurements of CH₄ emissions to the atmosphere followed a lognormal distribution pattern in both sites, and mean rates were 30× greater in the bog site. Rates of CH₄ production measured in vitro were initially 3× greater in the bog than in the conifer swamp; although, after 30 days of incubation, production rates were similar suggesting that in situ environmental conditions limited production in the conifer swamp. Amplified ribosomal DNA restriction analysis (ARDRA) and rarefaction techniques indicated that both sites had similar levels of archaeal richness, with 27 unique taxa in the bog and 23 taxa in the conifer swamp. However, the bog had more pronounced dominance of a few taxa, whereas the conifer swamp had more even distribution among taxa. A 16S rRNA gene sequence-based phylogenetic analysis indicated high levels of diversity with similarity to known methanogenic families Methanosarcinaceae, Methanosaetaceae, Methanobacteriaceae, and likely Methanomicrobiaceae as well as two additional lineages previously characterized as groups of yet uncultivated Euryarchaeota commonly occurring in flooded rice soils. Therefore, sites with low and high rates of CH₄ production supported very diverse methanogenic communities.     

Vegetation and environment of a New Zealand raised bog

Abstract. The vegetation of a mire in a medium‐high rainfall area of South Island, New Zealand is described. The central part of the bog is raised 6 m above the surroundings, suggesting that it is ombrotrophic, and the species present are those of apparently ombrotrophic bogs elsewhere in New Zealand. pH of < 4.0 and Ca/Mg molar quotient of < 1.0 also indicates ombrotrophic conditions. Within the mire, these criteria provide effective discrimination between the fen (rheotrophic) and bog (ombrotrophic) communities. A bimodal distribution of ordination scores suggests that the change in pH and in Ca/Mg quotients cause a switch to operate.     

Activity and metabolic regulation of methane production in deep peat profiles of boreal bogs

The potential activity of methane production was determined in the vertical profiles of the peat deposits of three bogs in Tver oblast, which were representative of the boreal zone. In the minerotrophic fen, the rates of methane production measured throughout the profile did not change significantly with depth and comprised 3–6 ng CH₄-C g^?1 h^?1. In ombrotrophic peat bogs, the rate did not exceed 5 ng CH₄-C g^?1 h^?1 in the upper layer of the profile (up to 1.5 m) and increased to 15–30 ng CH₄-C g^?1 h^?1 in the deep layers of the peat deposits. The distribution of fermentative microorganisms and methanogens in the profiles of peat deposits was uniform in all the studied bogs. In bog water samples, the presence of butyrate (up to 14.1 mg 1^?1) and acetate (up to 2.4 mg 1^?1) was revealed throughout the whole profile; in the upper 0.5-m layer of the ombrotrophic bogs, formate (up to 8.9 mg 1^?1) and propionate (up to 0.3 mg 1^?1) were detected as well. The arrangement of local maxima of the fatty acid content and methanogenic activity in the peat deposits, as well as the decrease in the acetate concentrations during summer, support the hypothesis that the initial substrates for methanogenesis come from the upper peat layers. It was established that the addition of sulfate and nitrate inhibits methane production in peat samples; the changes in the concentrations, recorded in situ, may also influence the methane content in peat layers.     

Hydrogenotrophic Methanogenesis by Moderately Acid-Tolerant Methanogens of a Methane-Emitting Acidic Peat

The emission of methane (1.3 mmol of CH₄ m⁻² day⁻¹), precursors of methanogenesis, and the methanogenic microorganisms of acidic bog peat (pH 4.4) from a moderately reduced forest site were investigated by in situ measurements, microcosm incubations, and cultivation methods, respectively. Bog peat produced CH₄ (0.4 to 1.7 μmol g [dry wt] of soil⁻¹ day⁻¹) under anoxic conditions. At in situ pH, supplemental H₂-CO₂, ethanol, and 1-propanol all increased CH₄ production rates while formate, acetate, propionate, and butyrate inhibited the production of CH₄; methanol had no effect. H₂-dependent acetogenesis occurred in H₂-CO₂-supplemented bog peat only after extended incubation periods. Nonsupplemented bog peat initially produced small amounts of H₂ that were subsequently consumed. The accumulation of H₂ was stimulated by ethanol and 1-propanol or by inhibiting methanogenesis with bromoethanesulfonate, and the consumption of ethanol was inhibited by large amounts of H₂; these results collectively indicated that ethanol- or 1-propanol-utilizing bacteria were trophically associated with H₂-utilizing methanogens. A total of 10⁹ anaerobes and 10⁷ hydrogenotrophic methanogens per g (dry weight) of bog peat were enumerated by cultivation techniques. A stable methanogenic enrichment was obtained with an acidic, H₂-CO₂-supplemented, fatty acid-enriched defined medium. CH₄ production rates by the enrichment were similar at pH 4.5 and 6.5, and acetate inhibited methanogenesis at pH 4.5 but not at pH 6.5. A total of 27 different archaeal 16S rRNA gene sequences indicative of Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae were retrieved from the highest CH₄-positive serial dilutions of bog peat and methanogenic enrichments. A total of 10 bacterial 16S rRNA gene sequences were also retrieved from the same dilutions and enrichments and were indicative of bacteria that might be responsible for the production of H₂ that could be used by hydrogenotrophic methanogens. These results indicated that in this acidic bog peat, (i) H₂ is an important substrate for acid-tolerant methanogens, (ii) interspecies hydrogen transfer is involved in the degradation of organic carbon, (iii) the accumulation of protonated volatile fatty acids inhibits methanogenesis, and (iv) methanogenesis might be due to the activities of methanogens that are phylogenetic members of the Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae.