Sedge Succession and Peatland Methane Dynamics: A Potential Feedback to Climate Change

Under the warmer climate, predicted for the future, northern peatlands are expected to become drier. This drying will lower the water table and likely result in reduced emissions of methane (CH₄) from these ecosystems. However, the prediction of declining CH₄ fluxes does not consider the potential effects of ecological succession, particularly the invasion of sedges into currently wet sites (open water pools, low lawns). The goal of this study was to characterize the relationship between the presence of sedges in peatlands and CH₄ efflux under natural conditions and under a climate change simulation (drained peatland). Methane fluxes, gross ecosystem production, and dissolved pore water CH₄ concentrations were measured and a vegetation survey was conducted in a natural and drained peatland near St. Charles-de-Bellechasse, Quebec, Canada, in the summer of 2003. Each peatland also had plots where the sedges had been removed by clipping. Sedges were larger, more dominant, and more productive at the drained peatland site. The natural peatland had higher CH₄ fluxes than the drained peatland, indicating that drainage was a significant control on CH₄ flux. Methane flux was higher from plots with sedges than from plots where sedges had been removed at the natural peatland site, whereas the opposite case was observed at the drained peatland site. These results suggest that CH₄ flux was enhanced by sedges at the natural peatland site and attenuated by sedges at the drained peatland site. However, the attenuation of CH₄ flux due to sedges at the drained site was reduced in wetter periods. This finding suggests that CH₄ flux could be decreased in the event of climate warming due to the greater depth to the water table, and that sedges colonizing these areas could further attenuate CH₄ fluxes during dry periods. However, during wet periods, the sedges may cause CH₄ fluxes to be higher than is currently predicted for climate change scenarios.     

Depth related diversity of methanogen Archaea in Finnish oligotrophic fen

The annual rate of CH₄ release and potential CH₄ production has recently been studied in the Salmisuo fen in eastern Finland but the microbiota responsible for the CH₄ production has not been examined. The diversity of the methane producing Archaea was analysed, at different depths, in the most representative microsite (Eriophorum lawn) of the fen. Methanogen populations were studied using primers amplifying a region of the methyl-coenzyme M reductase gene. PCR products were analysed by denaturing gradient gel electrophoresis and restriction fragment length polymorphism (RFLP) analysis of clone libraries. A representative of each RFLP group was sequenced. The study revealed a change of the methanogen populations with depth. Sequences from the upper layers of the fen grouped in a novel ‘Fen cluster’ and were related to Methanomicrobiales. Sequences retrieved from the deeper layers of the fen were related to Methanosarcinales via the Rice Cluster-I.     

Methane flux in relation to growth and phenology of a high yielding rice variety as affected by fertilization

Influence of urea application on growth parameters (shoot height, and weight, root volume, weight and porosity; number of tillers; grain yield) and their relationship with methane (CH₄) flux was investigated in Oryza sativa (var. Pant Dhan-4) under flooded soil condition. The study design consisted of (a) fertilized vegetated, (b) control vegetated, (c) fertilized bare, and (d) control bare plots. Crop growth and CH₄ flux measurements were conducted from 9 to 115 days of rice transplanting at regular intervals of 10 days. Results showed that there were significant differences due to days (dates of measurement) and fertilization in all growth parameters except shoot height. Day × fertilization interaction was significant for all growth parameters. CH₄ fluxes ranged from 0.4 to 20.2, 0.1 to 11.9, 0.09 to 2.2 and 0.004 to 1.5 mg m^-2 h^-1 under treatments (a), (b), (c) and (d), respectively. Maximum CH₄ flux was recorded at the flowering stage. All the growth parameters, including number of tillers, showed strong positive relationship with total methane flux. Root porosity was also strongly correlated with total CH₄ emission. It was concluded that CH₄ emission was substantially influenced by crop phenology and growth, and fertilization. The study emphasizes the substrate production and conduit effects of rice plants on CH₄ flux.     

Fluxes of nitrous oxide and methane from nitrogen-amended soils in a Colorado alpine ecosystem

In order to determine the effect of increased nitrogen inputs on fluxed of N₂O and CH₄ from alpine soils, we measured fluxes of these gases from fertilized and unfertilized soils in wet and dry alpine meadows. In the dry meadow, the addition of nitrogen resulted in a 22-fold increase in N₂O emissions, while in the wet meadow, we observed a 45-fold increase in N₂O emission rates. CH₄ uptake in the dry meadow was reduced 52% by fertilization; however, net CH₄ production occurred in all the wet meadow plots and emission rates were not significantly affected by fertilization. Net nitrification rates in the dry meadow were higher in fertilized plots than in non-fertilized plots throughout the growing season; net mineralization rates in fertilized dry meadow pots were higher than those in non-fertilized plots during the latter half of the growing season.     

Methanogen diversity and community composition in peatlands of the central to northern Appalachian Mountain region, North America

Methanogenic archaea are ubiquitous in peat soils; however, their diversity and distributions within and among peatland ecosystems are not well known. We used comprehensive clone libraries of 16S rRNA gene sequences to investigate spatial patterns in diversity (richness, evenness of taxa) and composition (taxonomic, phylogenetic) of the methanogenic community in six peatlands arrayed 775?km from eastern Ontario, Canada to West Virginia, USA. Five sites were Sphagnum (moss) and shrub dominated; one site was sedge dominated; and, potential rates of methane (CH₄) production ranged from 15 to 450?nmol/g?day. The gradient allowed us to examine influences of site conditions, site history, and climate on community composition. The region had representatives of methanogens from four taxonomic orders. We observed 29 operationally defined units (OTUs) based on >97% sequence identity. One OTU accounted for 43% of all clones, whereas 15 OTUs were rare with <1% of the total number of clones. The number of OTUs per site ranged from 4 to 21, and statistical analysis suggested diversity of 4–43 per site. Eighteen of the OTUs were endemic to one site; albeit, most endemics occurred in the sedge dominated site. One OTU was cosmopolitan, occurring in all six sites. We found a positive relationship between methanogen diversity and rates of CH₄ production per site (Pearson r?=?0.93). Turnover in community composition between sites was weakly related to geographic distance between sites, whereas variation in soil pH and annual temperature played larger roles. About 50% of the variation in community composition was unexplained by distance, pH, mean climate, and site age. We conclude that methanogen diversity in peatlands of the central Appalachian region is shaped by present-day environmental conditions, suggesting an influence of impending climatic and environmental changes.     

Vegetation heterogeneity and ditches create spatial variability in methane fluxes from peatlands drained for forestry

Drainage of peatlands for forestry starts a succession of ground vegetation in which mire species are gradually replaced by forest species. Some mire plant communities vanish quickly following the water-level drawdown; some may prevail longer in the moister patches of peatland. Drainage ditches, as a new kind of surface, introduce another component of spatial variation in drained peatlands. These variations were hypothesized to affect methane (CH₄) fluxes from drained peatlands. Methane fluxes from different plant communities and unvegetated surfaces, including ditches, were measured at the drained part of Lakkasuo mire, Central Finland. The fluxes were found to be related to peatland site type, plant community, water-table position and soil temperature. At nutrient-rich fen sites fluxes between plant communities differed only a little: almost all plots acted as CH₄ sinks (−0.9 to −0.4 mg CH₄ m⁻² d⁻¹), with the exception of Eriophorum angustifolium Honck. communities, which emitted 0.9 g CH₄ m⁻² d⁻¹. At nutrient-poor bog site the differences between plant communities were clearer. The highest emissions were measured from Eriophorum vaginatum L. communities (29.7 mg CH₄ m⁻² d⁻¹), with a decreasing trend to Sphagna (10.0 mg CH₄ m⁻² d⁻¹) and forest moss communities (2.6 mg CH₄ m⁻² d⁻¹). CH₄ emissions from different kinds of ditches were highly variable, and extremely high emissions (summertime averages 182–600 mg CH₄ m⁻² d⁻¹) were measured from continuously water-covered ditches at the drained fen. Variability in the emissions was caused by differences in the origin and movement of water in the ditches, as well as differences in vegetation communities in the ditches. While drainage on average greatly decreases CH₄ emissions from peatlands, a great spatial variability in fluxes is emerged. Emissions from ditches constantly covered with water, may in some cases have a great impact on the overall CH₄ emissions from drained peatlands.     

Long-term water table manipulations alter peatland gaseous carbon fluxes in Northern Michigan

Northern peatland water table position is tightly coupled to carbon (C) cycling dynamics and is predicted to change from shifts in temperature and precipitation patterns associated with global climate change. However, it is uncertain how long-term water table alterations will alter C dynamics in northern peatlands because most studies have focused on short-term water table manipulations. The goal of our study was to quantify the effect of long-term water table changes (~80 years) on gaseous C fluxes in a peatland in the Upper Peninsula of Michigan. Chamber methods were utilized to measure ecosystem respiration (ER), gross primary production (GPP), net ecosystem exchange (NEE), and methane (CH₄) fluxes in a peatland experiencing levee induced long-term water table drawdown and impoundment in relation to an unaltered site. Inundation raised water table levels by approximately ~10 cm and resulted in a decrease in ER and GPP, but an increase of CH₄ emissions. Conversely, the drained sites, with water table levels ~15 cm lower, resulted in a significant increase in ER and GPP, but a decrease in CH₄ emissions. However, NEE was not significantly different between the water table treatments. In summary, our data indicates that long-term water table drawdown and inundation was still altering peatland gaseous C fluxes, even after 80 years. In addition, many of the patterns we found were of similar magnitude to those measured in short-term studies, which indicates that short-term studies might be useful for predicting the direction and magnitude of future C changes in peatlands.     

CH4 production and oxidation processes in a boreal fen ecosystem after long‐term water table drawdown

Fens, which extend over vast areas in the Northern hemisphere, are sources of the greenhouse gas CH₄. Climate change scenarios predict a lowering water table (WT) in mires. To study the effect of WT drawdown on CH₄ dynamics in a fen ecosystem, we took advantage of a WT drawdown gradient near a ground water extraction plant. Methane fluxes and CH₄ production and oxidation potentials were related to microbial communities responsible for the processes in four mire locations (wet, semiwet, semidry, and dry). Principal component analyses performed on the vegetation, pH, CH₄, and WT results clearly separated the four sampling locations in the gradient. Long‐term lowering of WT was associated with decreased coverage of Sphagnum and aerenchymatic plants, decreased CH₄ field emissions and CH₄ production potential. Based on mcrA terminal restriction fragment length polymorphism the methanogen community structure correlated best with the methane production and coverage of aerenchymatic plants along the gradient. Methanosarcinaceae and Methanocellales were found at the pristine wet end of the gradient, whereas the Fen cluster characterized the dry end. The methane‐oxidizing bacterial community consisted exclusively of Methylocystis bacteria, but interestingly of five different alleles (T, S, R, M, and O) of the particulate methane monooxygenase marker gene pmoA. The M allele was dominant in the wet locations, and the occurrence of alleles O, S, and T increased with drainage. The occurrence of the R allele that characterized the upper peat layer correlated with CH₄ oxidation potential. These results advance our understanding of mire dynamics after long‐term WT drawdown and of the microbiological bases of methane emissions from mires.     

Long‐term nutrient addition increases respiration and nitrous oxide emissions in a New England salt marsh

Salt marshes may act either as greenhouse gas (GHG) sources or sinks depending on hydrological conditions, vegetation communities, and nutrient availability. In recent decades, eutrophication has emerged as a major driver of change in salt marsh ecosystems. An ongoing fertilization experiment at the Great Sippewissett Marsh (Cape Cod, USA) allows for observation of the results of over four decades of nutrient addition. Here, nutrient enrichment stimulated changes to vegetation communities that, over time, have resulted in increased elevation of the marsh platform. In this study, we measured fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in dominant vegetation zones along elevation gradients of chronically fertilized (1,572 kg N ha^?1 year^?1) and unfertilized (12 kg N ha^?1 year^?1) experimental plots at Great Sippewissett Marsh. Flux measurements were performed using darkened chambers to focus on community respiration and excluded photosynthetic CO₂ uptake. We hypothesized that N‐replete conditions in fertilized plots would result in larger N₂O emissions relative to control plots and that higher elevations caused by nutrient enrichment would support increased CO₂ and N₂O and decreased CH₄ emissions due to the potential for more oxygen diffusion into sediment. Patterns of GHG emission supported our hypotheses. Fertilized plots were substantially larger sources of N₂O and had higher community respiration rates relative to control plots, due to large emissions of these GHGs at higher elevations. While CH₄ emissions displayed a negative relationship with elevation, they were generally small across elevation gradients and nutrient enrichment treatments. Our results demonstrate that at decadal scales, vegetation community shifts and associated elevation changes driven by chronic eutrophication affect GHG emission from salt marshes. Results demonstrate the necessity of long‐term fertilization experiments to understand impacts of eutrophication on ecosystem function and have implications for how chronic eutrophication may impact the role that salt marshes play in sequestering C and N.     

Fluxes of nitrous oxide and methane from drained peatlands following forest clear-felling in southern Finland

Drainage of waterlogged sites has been part of the normal forestry practice in Fennoscandia, the Baltic countries, the British Isles and in some parts of Russia since the early 20^th century, and currently, about 15 million hectares of peatlands and other wetlands have been drained for forestry purposes. The rate of forest clear-felling on drained peatlands will undergo a rapid increase in the near future, when a large number of these forests approach their regeneration age. A small-scale pilot survey was performed at two nutrient-rich and old peatland drainage areas in southern Finland to study if forest clear-felling has significant impacts on the exchange of nitrous oxide (N₂O) and methane (CH₄) between soil and atmosphere. The average N₂O emissions from the two drainage areas during three growing seasons following clear-felling were 945 and 246 g m^–2 d^–1. The corresponding CH₄ fluxes were –0.07 and –0.52 mg m^–2 d^–1. Clear-felling had impacts on the environmental factors known to affect the N₂O and CH₄ fluxes of peatlands, i.e. clear-felling raised the water table level and increased the peat temperature. However, no substantial changes in the fluxes of CH₄ following clear-felling were observed. The results concerning N₂O indicated a potential for increased emissions following clear-felling of drained peatland forests, but further studies are needed for a critical evaluation of the impacts of clear-felling on the fluxes of CH₄ and N₂O.     

Effects of algal and terrestrial carbon on methane production rates and methanogen community structure in a temperate lake sediment

1. Sources of atmospheric CH₄ are both naturally occurring and anthropogenic. In fact, some anthropogenic activities may influence the production of CH₄ from natural sources, such as lakes. 2. Ongoing changes in the catchment of lakes, including eutrophication and increased terrestrial organic carbon export, may affect CH₄ production rates as well as shape methanogen abundance and community structure. Therefore, inputs from catchments to lakes should be examined for their effects on CH₄ production. 3. We added algal and terrestrial carbon separately to lake sediment cores and measured CH₄ production. We also used quantitative polymerase chain reaction and terminal restriction fragment length polymorphism to determine the effects of these carbon additions on methanogen abundance and community composition. 4. Our results indicate that CH₄ production rates were significantly elevated following the addition of algal biomass. Terrestrial carbon addition also appeared to increase methanogenesis rates; however, the observed increase was not statistically significant. 5. Interestingly, increased CH₄ production rates resulted from increases in per‐cell activity rather than an increase in methanogen abundance or community compositional shifts, as indicated by our molecular analyses. 6. Overall, anthropogenic impacts on aquatic ecosystems can influence methanogenesis rates and should be considered in models of global methane cycling and climate.     

Effect of peat re-wetting on carbon and nutrient fluxes, greenhouse gas production and diversity of methanogenic archaeal community

Many peatlands were affected by drainage in the past, and restoration of their water regime aims to bring back their original functions. The purpose of our study was to simulate re-wetting of soils of different types of drained peatlands (bogs and minerotrophic mires, located in the Sumava Mountains, Czech Republic) under laboratory conditions (incubation for 15 weeks) and to assess possible risks of peatland water regime restoration - especially nutrient leaching and the potentials for CO₂ and CH₄ production. After re-wetting of soils sampled from drained peatlands (simulated by anaerobic incubation) (i) phosphorus concentration (SRP) did not change in any soil, (ii) concentration of ammonium and dissolved organic nitrogen (DON) increased, but only in a drained fen, (iii) DOC increased significantly in the drained fen and degraded drained bog, (iv) CO₂ production decreased, (v) CH₄ production and the number of methanogens increased in all soils, and (vi) archaeal methanogenic community composition was also affected by re-wetting; it differed significantly between drained and pristine fens, whereas it was more similar between drained and pristine bogs. Overall, the soils from fens reacted more dynamically to re-wetting than the bogs, and therefore, some nutrients (especially nitrogen) and DOC leaching may be expected from drained fens after their water regime restoration. However, if compared to their state before restoration, ammonium and phosphorus leaching should not increase and leaching of nitrates and DON should even decrease after restoration, especially during the vegetation season. Further, CO₂ production in soils of fens and bogs should decrease after their water regime restoration, whereas CH₄ production in soils should increase. However, we cannot derive any clear conclusions about CH₄ emissions from the ecosystems based on this study, as they depend strongly on environmental factors and on the actual activity of methanotrophs in situ.     

Network analysis and functional estimation of the microbiome reveal the effects of cashew nut shell liquid feeding on methanogen behaviour in the rumen

The effects of cashew nut shell liquid (CNSL) feeding on the methane (CH₄) emission and the ruminal microbiome of Lai Sind beef cattle were investigated. Changes in the methane production and rumen microbiome by CNSL feeding were monitored by a respiration chamber and 16S rRNA gene amplicon sequencing respectively. The results demonstrated that CNSL feeding mitigated 20.2%–23.4% of the CH₄ emission in vivo without apparent adverse effects on feed intake and feed digestibility. The rumen fluid analysis revealed a significant increase in the proportion of propionate in the total short-chain fatty acids. The relative abundance of methanogen (order Methanobacteriales) decreased significantly, indicating the direct inhibitory effect of CNSL on methanogens. The predicted function of the rumen microbiome indicated that carbohydrate and lipid metabolisms including propionate production were upregulated by CNSL feeding, whereas CH₄ metabolism was downregulated. A network analysis revealed that methanogen changed its partner bacteria after CNSL feeding. The δ¹³C of CH₄ ranged from −74.2‰ to −66.6‰ with significant fluctuation by CNSL feeding, in agreement with the shift of the rumen microbiome. Our findings demonstrate that CNSL feeding can mitigate the CH₄ emission from local cattle production systems in South-East Asia by modifying the rumen microbiome and its function.     

Relationship between rumen methanogens and methane production in dairy cows fed diets supplemented with a feed enzyme additive

Aims: To investigate the relationship between ruminal methanogen community and host enteric methane (CH₄) production in lactating dairy cows fed diets supplemented with an exogenous fibrolytic enzyme additive. Methods and Results: Ecology of ruminal methanogens from dairy cows fed with or without exogenous fibrolytic enzymes was examined using PCR–denaturing gradient gel electrophoresis (PCR–DGGE) analyses and quantitative real‐time PCR (qRT‐PCR). The density of methanogens was not affected by the enzyme additive or sampling times, and no relationship was observed between the total methanogen population and CH₄ yield (as g per head per day or g kg^?1 DMI). The PCR–DGGE profiles consisted of 26 distinctive bands, with two bands similar to Methanogenic archaeon CH1270 negatively correlated, and one band similar to Methanobrevibacter gottschalkii strain HO positively correlated, with CH₄ yield. Three bands similar to Methanogenic archaeon CH1270 or Methanobrevibacter smithii ATCC 35061 appeared after enzyme was added. Conclusions: Supplementing a dairy cow diet with an exogenous fibrolytic enzyme additive increased CH₄ yield and altered the composition of the rumen methanogen community, but not the overall density of methanogens. Significance and Impact of the Study: This is the first study to identify the correlation between methanogen ecology and host CH₄ yield from lactating dairy cows.     

Impact of winter roads on boreal peatland carbon exchange

Across Canada's boreal forest, linear disturbances, including cutlines such as seismic lines and roads, crisscross the landscape to facilitate resource exploration and extraction; many of these linear disturbances cross peatland ecosystems. Changes in tree canopy cover and the compression of the peat by heavy equipment alter local thermal, hydrological, and ecological conditions, likely changing carbon exchange on the disturbance, and possibly in the adjacent peatland. We measured bulk density, water table, soil temperature, plant cover, and CO₂ and CH₄ flux along triplicate transects crossing a winter road through a wooded fen near Peace River, Alberta, Canada. Sample plots were located 1, 5, and 10 m from the road on both sides with an additional three plots on the road. Productivity of the overstory trees, when present, was also determined. The winter road had higher bulk density, shallower water table, higher graminoid cover, and thawed earlier than the adjacent peatland. Tree productivity and CO₂ flux varied between the plots, and there was no clear pattern in relation to distance from the road. The plots on the winter road acted as a greater CO₂ sink and greater CH₄ source compared to the adjacent peatland with plots on the winter road emitting on average (standard error) 479 (138) compared to 41 (10) mg CH₄ m^?2 day^?1 in the adjacent peatland. Considering both gases, global warming potential increased from 70 to 250 g CO₂e m^?2 year^?1 in the undisturbed area to 2100 g CO₂e m^?2 year^?1 on the winter road. Although carbon fluxes on any given cutline through peatland will vary depending on level of compaction, line width and vegetation community shifts, the large number of linear disturbances in Canada's boreal forest and slow recovery on peatland ecosites suggest they could represent an important anthropogenic greenhouse gas source.     

Enhanced winter soil frost reduces methane emission during the subsequent growing season in a boreal peatland

Winter climate change may result in reduced snow cover and could, consequently, alter the soil frost regime and biogeochemical processes underlying the exchange of methane (CH₄) in boreal peatlands. In this study, we investigated the short‐term (1–3 years) vs. long‐term (11 years) effects of intensified winter soil frost (induced by experimental snow exclusion) on CH₄ exchange during the following growing season in a boreal peatland. In the first 3 years (2004–2006), lower CH₄ emissions in the treatment plots relative to the control coincided with delayed soil temperature increase in the treatment plots at the beginning of the growing season (May). After 11 treatment years (in 2014), CH₄ emissions were lower in the treatment plots relative to the control over the entire growing season, resulting in a reduction in total growing season CH₄ emission by 27%. From May to July 2014, reduced sedge leaf area coincided with lower CH₄ emissions in the treatment plots compared to the control. From July to August, lower dissolved organic carbon concentrations in the pore water of the treatment plots explained 72% of the differences in CH₄ emission between control and treatment. In addition, greater Sphagnum moss growth in the treatment plots resulted in a larger distance between the moss surface and the water table (i.e., increasing the oxic layer) which may have enhanced the CH₄ oxidation potential in the treatment plots relative to the control in 2014. The differences in vegetation might also explain the lower temperature sensitivity of CH₄ emission observed in the treatment plots relative to the control. Overall, this study suggests that greater soil frost, associated with future winter climate change, might substantially reduce the growing season CH₄ emission in boreal peatlands through altering vegetation dynamics and subsequently causing vegetation‐mediated effects on CH₄ exchange.     

The response of denitrifiers in a sandy loam soil affected by a long-term fertilization to organic carbon and nitrate

The response of denitrifiers to carbon in the form of glucose (Glc-C) and nitrate (NO ₃ ⁻ -N) amendments was studied in four differently fertilized plots of sandy-loam soil. Two basically different characteristics of denitrification activity were determined: (1) potential denitrification measured as nitrous oxide production during 1-d incubation in the presence of acetylene, and (2) denitrifying enzyme activity determined in soil slurries as a N₂O production in the presence of acetylene and chloramphenicol during 1 h of incubation. Potential denitrification was strongly influenced by both Glc-C and NO ₃ ⁻ -N amendments in their various combinations, but was also affected by the fertilization practice. The response of denitrifiers to Glc-C and NO ₃ ⁻ -N was generally lower in unfertilized and surprisingly also in highly fertilized soils than in organically and moderately fertilized soils. Denitrifying enzyme activity was stimulated by the fertilization and was, in contrast to potential denitrification, the highest in highly fertilized soil. The results indicate that although active denitrifiers were present in a highly fertilized soil, their ability to develop under optimal conditions was decreased (being similar to that of denitrifiers in unfertilized soil). This suggests long-term changes in soil microbial community in a highly fertilized soil, presumably connected to changes in soil chemistry caused by fertilization.     

Methane Production in Minnesota Peatlands

Rates of methane production in Minnesota peats were studied. Surface (10- to 25-cm) peats produced an average of 228 nmol of CH₄ per g (dry weight) per h at 25°C and ambient pH. Methanogenesis rates generally decreased with depth in ombrotrophic peats, but on occasion were observed to rise within deeper layers of certain fen peats. Methane production was temperature dependent, increasing with increasing temperature (4 to 30°C), except in peats from deeper layers. Maximal methanogenesis from these deeper regions occurred at 12°C. Methane production rates were also pH dependent. Two peats with pHs of 3.8 and 4.3 had an optimum rate of methane production at pH 6.0. The addition to peat of glucose and H₂-CO₂ stimulated methanogenesis, whereas the addition of acetate inhibited methanogenesis. Cysteine-sulfide, nitrogen-phosphorus-trace metals, and vitamins-yeast extract affected methane production very little. Various gases were found to be trapped or dissolved (or both) within peatland waters. Dissolved methane increased linearly to a depth of 210 cm. The accumulation of metabolic end products produced within peat bogs appears to be an important mechanism limiting carbon turnover in peatland environments.     

Microbial sensitivity to temperature and sulfate deposition modulates greenhouse gas emissions from peat soils

Peatlands are among the largest natural sources of atmospheric methane (CH₄) worldwide. Microbial processes play a key role in regulating CH₄ emissions from peatland ecosystems, yet the complex interplay between soil substrates and microbial communities in controlling CH₄ emissions as a function of global change remains unclear. Herein, we performed an integrated analysis of multi-omics data sets to provide a comprehensive understanding of the molecular processes driving changes in greenhouse gas (GHG) emissions in peatland ecosystems with increasing temperature and sulfate deposition in a laboratory incubation study. We sought to first investigate how increasing temperatures (4, 21, and 35°C) impact soil microbiome–metabolome interactions; then explore the competition between methanogens and sulfate-reducing bacteria (SRBs) with increasing sulfate concentrations at the optimum temperature for methanogenesis. Our results revealed that peat soil organic matter degradation, mediated by biotic and potentially abiotic processes, is the main driver of the increase in CO₂ production with temperature. In contrast, the decrease in CH₄ production at 35°C was linked to the absence of syntrophic communities and the potential inhibitory effect of phenols on methanogens. Elevated temperatures further induced the microbial communities to develop high growth yield and stress tolerator trait-based strategies leading to a shift in their composition and function. On the other hand, SRBs were able to outcompete methanogens in the presence of non-limiting sulfate concentrations at 21°C, thereby reducing CH₄ emissions. At higher sulfate concentrations, however, the prevalence of communities capable of producing sufficient low-molecular-weight carbon substrates for the coexistence of SRBs and methanogens was translated into elevated CH₄ emissions. The use of omics in this study enhanced our understanding of the structure and interactions among microbes with the abiotic components of the system that can be useful for mitigating GHG emissions from peatland ecosystems in the face of global change.