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Northern peatlands are experiencing more frequent and severe fire events as a result of changing climate conditions. Recent studies show that such a fire-regime change imposes a direct climate-warming impact by emitting large amounts of carbon into the atmosphere. However, the fires also convert parts of the burnt biomass into pyrogenic carbon. Here, we show a potential climate-cooling impact induced by fire-derived pyrogenic carbon in laboratory incubations. We found that the accumulation of pyrogenic carbon reduced post-fire methane production from warm (32 °C) incubated peatland soils by 13-24%. The redox-cycling, capacitive, and conductive electron transfer mechanisms in pyrogenic carbon functioned as an electron snorkel, which facilitated extracellular electron transfer and stimulated soil alternative microbial respiration to suppress methane production. Our results highlight an important, but overlooked, function of pyrogenic carbon in neutralizing forest fire emissions and call for its consideration in the global carbon budget estimation.

Peatlands are an important source of the atmospheric greenhouse gas methane (CH4). Although CH4 cycling and fluxes have been quantified for many northern peatlands, imprecision in process-based approaches to predicting CH4 emissions suggests that our understanding of underlying processes is incomplete. Microbial anaerobic oxidation of CH4 (AOM) is an important CH4 sink in marine sediments, but AOM has only recently been identified in a few nonmarine systems. We used (13)C isotope tracers and followed the fate of (13)C into CO2 and peat in order to study the geographic extent, relative importance, and biogeochemistry of AOM in 15 North American peatlands spanning a ∼1500 km latitudinal transect that varied in hydrology, vegetation, and soil chemistry. For the first time, we demonstrate that AOM is a widespread and quantitatively important process across many peatland types and that anabolic microbial assimilation of CH4-C occurs. However, AOM rate is not predicted by CH4 production rates and the primary mechanism of C assimilation remains uncertain. AOM rates are higher in fen than bog sites, suggesting electron acceptor constraints on AOM. Nevertheless, AOM rates were not correlated with porewater ion concentrations or stimulated following additions of nitrate, sulfate, or ferric iron, suggesting that an unidentified electron acceptor(s) must drive AOM in peatlands. Globally, we estimate that AOM could consume a large proportion of CH4 produced annually (1.6-49 Tg) and thereby constrain emissions and greenhouse gas forcing.

The active methanotroph community was investigated in two contrasting North American peatlands, a nutrient-rich sedge fen and nutrient-poor Sphagnum bog using in vitro incubations and (13)C-DNA stable-isotope probing (SIP) to measure methane (CH(4)) oxidation rates and label active microbes followed by fingerprinting and sequencing of bacterial and archaeal 16S rDNA and methane monooxygenase (pmoA and mmoX) genes. Rates of CH(4) oxidation were slightly, but significantly, faster in the bog and methanotrophs belonged to the class Alphaproteobacteria and were similar to other methanotrophs of the genera Methylocystis, Methylosinus, and Methylocapsa or Methylocella detected in, or isolated from, European bogs. The fen had a greater phylogenetic diversity of organisms that had assimilated (13)C, including methanotrophs from both the Alpha- and Gammaproteobacteria classes and other potentially non-methanotrophic organisms that were similar to bacteria detected in a UK and Finnish fen. Based on similarities between bacteria in our sites and those in Europe, including Russia, we conclude that site physicochemical characteristics rather than biogeography controlled the phylogenetic diversity of active methanotrophs and that differences in phylogenetic diversity between the bog and fen did not relate to measured CH(4) oxidation rates. A single crenarchaeon in the bog site appeared to be assimilating (13)C in 16S rDNA; however, its phylogenetic similarity to other CO(2)-utilizing archaea probably indicates that this organism is not directly involved in CH(4) oxidation in peat.

Peatlands are important sources of CH(4) emissions to the atmosphere and molecular surveys have identified a diverse, but mainly uncultured, euryarchaeal community in them. Characterization of a strain, E1-9c(T), associated with uncultured group E1, from a minerotrophic fen is reported. Cells were regular cocci, usually found in pairs, that stained Gram-positive and were resistant to lysis by 0.1 % SDS. Multiple flagella were observed, but motility was not observed in wet mounts. Optimal growth was obtained at moderate temperatures (28-30 degrees C) and slightly acidic pH (5.5). Total Na(+) and NaCl were only tolerated at concentrations less than 100 mM and 0.5 %, respectively, and Na(2)S concentrations above 0.1 mM were inhibitory. H(2)/CO(2) and formate were the only methanogenic substrates used by E1-9c(T); formate concentrations above 50 mM were inhibitory for growth. Vitamins, coenzyme M and acetate (4 mM) were required for growth and the doubling time was about 19 h. Phylogenetic analysis of the 16S rRNA gene and inferred McrA amino acid sequences showed that E1-9c(T) represented an independent lineage within the order Methanomicrobiales. Physiological and phylogenetic comparisons with different members of the order supported classification of E1-9c(T) in a new genus in the Methanomicrobiales. The name Methanosphaerula palustris gen. nov., sp. nov. is proposed; strain E1-9c(T) (=ATCC BAA-1565(T) =DSM 19958(T)) is the type strain of Methanosphaerula palustris.

Minerotrophic fen peatlands are widely distributed in northern latitudes and, because of their rapid turnover of organic matter, are potentially larger sources of atmospheric methane than bog peatlands per unit area. However, studies of the archaeal community composition in fens are scarce particularly in minerotrophic sites. Several 16S rRNA-based primer sets were used to obtain a broad characterization of the archaeal community in a minerotrophic fen in central New York State. A wide archaeal diversity was observed in the site: 11 euryarchaeal and 2 crenarchaeal groups, most of which were uncultured. The E1 group, a novel cluster in the order Methanomicrobiales, and Methanosaetaceae were the codominant groups in all libraries and results of terminal restriction fragment length polymorphism (T-RFLP) analysis. Given its abundance and potential hydrogenotrophic methane contribution, the E1 group was targeted for culture attempts with a low-ionic-strength medium (PM1). Initial attempts yielded Methanospirillum-dominated cultures. However, by incorporating a T-RFLP analysis as a quick selection tool for treatments and replicates, we were able to select an enrichment dominated by E1. Further dilutions to 10(-9) and tracking with T-RFLP yielded a strain named E1-9c. E1-9c is a novel coccoid hydrogenotrophic, mesophilic, slightly acidophilic methanogen and is highly sensitive to Na(2)S concentrations (requires <0.12 mM for growth). We propose E1-9c as the first representative of a novel genus in the Methanomicrobiales order.

Two methanogenic cultures were enriched from acidic peat soil using a growth medium buffered to c. pH 5. One culture, 6A, was obtained from peat after incubation with H(2)/CO(2), whereas culture NTA was derived from a 10(-4) dilution of untreated peat into a modified medium. 16S rRNA gene clone libraries from each culture contained one methanogen and two bacterial sequences. The methanogen 16S rRNA gene sequences were 99% identical with each other and belonged to the novel "R-10/Fen cluster" family of the Methanomicrobiales, whereas their mcrA sequences were 96% identical. One bacterial 16S rRNA gene sequence from culture 6A belonged to the Bacteroidetes and showed 99% identity with sequences from methanogenic enrichments from German and Russian bogs. The other sequence belonged to the Firmicutes and was identical to a thick rod-shaped citrate-utilizing organism isolated from culture 6A, the numbers of which decreased when the Ti (III) chelator was switched from citrate to nitrilotriacetate. Bacterial clones from the NTA culture clustered in the Delta- and Betaproteobacteria. Both cultures contained thin rods, presumably the methanogens, as the predominant morphotype, and represent a significant advance in characterization of the novel acidiphilic R-10 family methanogens.

Acidic peatlands are among the largest natural sources of atmospheric methane and harbour a large diversity of methanogenic Archaea. Despite the ubiquity of methanogens in these peatlands, indigenous methanogens capable of growth at acidic pH values have resisted culture and isolation; these recalcitrant methanogens include members of an uncultured family-level clade in the Methanomicrobiales prevalent in many acidic peat bogs in the Northern Hemisphere. However, we recently succeeded in obtaining a mixed enrichment culture of a member of this clade. Here we describe its isolation and initial characterization. We demonstrate that the optimum pH for methanogenesis by this organism is lower than that of any previously described methanogen.

Members of the order Methanomicrobiales are abundant, and sometimes dominant, hydrogenotrophic (H2-CO2 utilizing) methanoarchaea in a broad range of anoxic habitats. Despite their key roles in greenhouse gas emissions and waste conversion to methane, little is known about the physiological and genomic bases for their widespread distribution and abundance. In this study, we compared the genomes of nine diverse Methanomicrobiales strains, examined their pangenomes, reconstructed gene flow and identified genes putatively mediating their success across different habitats. Most strains slowly increased gene content whereas one, Methanocorpusculum labreanum, evidenced genome downsizing. Peat-dwelling Methanomicrobiales showed adaptations centered on improved transport of scarce inorganic nutrients and likely use H+ rather than Na+ transmembrane chemiosmotic gradients during energy conservation. In contrast, other Methanomicrobiales show the potential to concurrently use Na+ and H+ chemiosmotic gradients. Analyses also revealed that the Methanomicrobiales lack a canonical electron bifurcation system (MvhABGD) known to produce low potential electrons in other orders of hydrogenotrophic methanogens. Additional putative differences in anabolic metabolism suggest that the dynamics of interspecies electron transfer from Methanomicrobiales syntrophic partners can also differ considerably. Altogether, these findings suggest profound differences in electron trafficking in the Methanomicrobiales compared with other hydrogenotrophs, and warrant further functional evaluations.

Spatial patterns of soil microbial activity are central to understanding greenhouse gas dynamics in wetlands. Because agriculture reduces spatial heterogeneity in soil properties, we examined the hypothesis that soil microbial activity in natural wetlands would show a high degree of spatial autocorrelation when distances between samples were small; however, in wetlands that were disturbed by agriculture these spatial patterns would occur across larger sampling distances or disappear due to homogenization. We examined the hypothesis via methane (CH 4 ) dynamics, respiration (as carbon dioxide (CO 2 ) production), and net nitrogen (N) mineralization in muck soils from a natural wetland dominated by sedges ( Carex lacustris ) either with or without grey alder ( Alnus rugosa ). The disturbed wetland had corn production or restoration with either reed canary grass ( Phalaris arundinacea ) or purple loosestrife ( Lythrum salicaria ) growing for about 10 years. Rates of anaerobic CH 4 production ranged from 0.1 to 12,370 nmol kg − 1 s − 1 with the largest rates in the natural wetland with alder; the Reed Canary Grass site exhibited extremely slow rates of CH 4 production. Oxic CH 4 consumption occurred only in soils from the natural wetland, with no activity in soils from the Corn site and the two Restored sites. Rates of CO 2 production ranged from − 76 to 388 nmol kg − 1 s − 1 under anoxic conditions and from 0.1 to 402 nmol kg − 1 s − 1 under oxic conditions, with the highest rates in natural wetland surface soils. Despite broad spatial variation in rates across all sites, spatial patterns of CH 4 , respiration, and net N mineralization displayed limited spatial dependence, with autocorrelation at distances < 8 m only in the Purple Loosestrife site. The results suggest that large sample sizes are needed to characterize the high variability present in microbial activity and greenhouse gases in muck soils, but explanation(s) for spatial variability remain elusive. [ABSTRACT FROM AUTHOR]

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 examined controls on mineralization of carbon to methane (CH[sub 4]) and carbon dioxide (CO[sub 2]) in Sphagnum (moss)-dominated peatland ecosystems by transplanting surface (5 cm deep) and subsurface (40 cm deep) peat samples reciprocally among three sites for periods ranging from 4 to 25 months. The sites were Big Run Bog in West Virginia, USA, Bog Lake Bog in Minnesota, USA, and Bog 307 in Ontario, Canada. Immediately upon retrieval, we incubated the peat samples in the laboratory at 12 and 22°C under both anoxic and oxic conditions to estimate rates of carbon mineralization. Transplanting affected surface peat more than subsurface peat. Peat incubated within Bog Lake Bog in Minnesota had the highest rates of CH[sub 4] production, regardless of origin, whereas transplanting did not affect rates of CO[sub 2] production measured concomitantly. Peat that originated in Big Run Bog in West Virginia generally maintained higher rates of CH[sub 4] production and CO[sub 2] production than peat from the other two sites after incubation in the field. The temperature dependence (Q[sub 10]) of CH[sub 4] production and CO[sub 2] production varied among transplant sites, but not among peat origins, suggesting physiological adaptations of microbial communities to local environmental conditions. Differences in organic matter quality of the peat, particularly lignin chemistry, helped explain the results: (a) CH[sub 4] production correlated with fresher lignin derived from Carex sedges, and (b) CO[sub 2] production correlated with woody lignin. We concluded that, although both site conditions (climate, nutrient status, and microbial communities) and organic matter quality influence carbon mineralization in peat, interactive effects occur and may differ depending on peat temperature. Moreover, CH[sub 4] production and CO[sub 2] production respond differently to environmental regulators. [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]

Although Sphagnum (moss)-dominated, northern peatland ecosystems harbor methane (CH4)-producing microorganisms (methanogens) and are a significant source of atmospheric CH4, rates of CH4 production vary widely among different systems. Very little work has been done to examine whether concentrations of cations and metal elements may account for the variability. We examined ratesof CH4 production in peat from five geographically and functionally disparate Sphagnum-dominated peatlands by incubating peat samples in vitro with and without additions of trace metals (Fe, Ni, Co) and base cations (Ca, Li, Na). In peat from the most mineral poorsites, the addition of metals and Na enhanced CH4 production beyond that observed in controls. The same treatments in mineral rich sites yielded no effect or an inhibition of CH4 production. None of the treatments affected anaerobic respiration, measured as CO2 production, in the in vitro incubations of peat, except added citrate, suggesting that methanogens, and not the entireanaerobic community, can be limited by the availability of metal elements and cations. [ABSTRACT FROM AUTHOR]

I examined differences in the biogeochemical cycles of CH4 and CO2 (fluxes, concentrations, production, CH4 oxidation) in Typha latifolia wetlands on silty clay sediment versus organic peat soil in central New York State to determine whether variation in the amount of organic matter in sediment or soil, or plant production on siteswith different organic matter content, affected variation in CH4 andCO2. I found very high temporal variation in CH4 within each site, precluding the detection of variation in CH4 as a function of sediment or soil organic matter content. In 1994, CH4 efflux from two peat sites to the atmosphere averaged 7 and 87 nmol m-2 s-1 compared to 89 and 408 nmol m-2 s-1 for two sediment sites. Mean CO2 efflux from the peat sites was 0.40 and 1.51 mumol m-2 s-1 compared to 1.02 and 1.65 mumol m-2 s-1 for the sediment sites. I assessed the role of plant production by experimentally removing T. latifolia shoots from small plots: this lowered CH4 efflux from the sediment site by 85%, suggesting that plants foster CH4 production in low organic matter sediment, but CH4 efflux was 14-times greater following shoot removal on one peat site. Shoot removal had no effect on CO2 efflux. Variations in temperature, dissolved organic carbon, and pCH4 in sediment or soil porewater explained the variation in CH4 efflux among the four study sites, whereas variation in net primary production explained the variation in CO2 efflux. [ABSTRACT FROM AUTHOR]