Abundance, biomass, structure, and activity of the microbial complexes of minerotrophic and ombrotrophic peatlands

Very large microbial biomass was revealed in peat bogs by means of fluorescence microscopy. In ombrotrophic peatlands, the pool of the dry-weight microbial biomass in the 1.5-m layer constituted 3-4 t/ha and was twice as high as in the minerotrophic peat bogs. Fungal biomass was predominant (55-99%) in ombrotrophic peatlands, while bacterial biomass predominated in minerotrophic peatlands (55-86%). In ombrotrophic peatlands, the microbial biomass was concentrated in the upper layers, while in minerotrophic peatlands, it was uniformly distributed in the bulk. After drainage, the microbial pool in the ombrotrophic peatlands increased twofold; that in the minerotrophic peatlands remained at the same level. The potential activity of nitrogen fixation and denitrification was revealed across the whole profile of the peatlands. The average values of these potential activities were five times higher in the minerotrophic peatlands, where bacterial biomass predominated.     

Fluxes of nitrous oxide from boreal peatlands as affected by peatland type,water table level and nitrification capacity

Peat soils with high nitrogen content are potential sources of nitrous oxide (N₂O). Fluxes of nitrous oxide were measuredin situ on nine virgin and ten drained peatlands of different hydrology and nutrient status. Numbers of nitrifying bacteria were estimated in different layers of the peat profiles with a most-probable-number technique. Nitrification potentials were determined in soil slurries of pH 4 and 6 from the profiles of six peat soils. Many virgin peatlands showed low N₂O uptake. Lowering of the water table generally increased the average fluxes of N₂O from the soils, although more in minerotrophic (nutrient rich) than in ombrotrophic (nutrient poor) sites. Ammonium oxidizing bacteria were found on only two sites but nitrite oxidizers were detected in almost all peat profiles. More nitrite oxidizers were found in drained than in virgin peat profiles. Nitrification was enhanced after lowering of the water table in minerotrophic peat but not in ombrotrophic peat. The N₂O fluxes correlated positively with the numbers of nitrite oxidizers, nitrification potential, N, P and Ca content and pH of the soil and negatively with the level of water table (expressed as negative values) and K content of the soil.     

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 l(-1)) and acetate (up to 2.4 mg l(-1)) was revealed throughout the whole profile; in the upper 0.5-m layer of the ombrotrophic bogs, formate (up to 8.9 mg l(-1)) and propionate (up to 0.3 mg l(-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.     

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.     

Patterns of Fungal and Bacterial Carbon Mineralization Across Northern European Peatlands

The fungal and bacterial activity was determined in 20 northern European peatlands ranging from ombrotrophic bogs to eutrophic fens with key differences in degree of humification, pH, dry bulk density, carbon (C) content and vegetation communities using the selective inhibition (SI) technique. These peatlands were partly disturbed and the respective water tables lowered below the surface layer. Basal respiration ranged from 24 to 128 µg CO₂-C g^?1 dry peat d^?1. Bacterial contributions to CO₂ production were high in most peatlands and showed the following pattern: eutrophic >> transitional ≥ mesotrophic >> ombrotrophic peatland types. The fungal-to-bacterial (F:B) ratios varied substantially within peatland type, and this was mainly attributed to differences in peat botanical compositions and chemistry. The computed mean Inhibitor Additivity Ratio (IAR) was quite close to 1 to suggest that the SI techniques can be used to partition eukaryotic and prokaryotic activity in wide range of peatlands. Overall, basal respiration, microbial biomass-C, fungal and bacterial activities varied across the studied peatland types, and such differences could have consequences for C- and nutrient-cycling as well as how bogs and fens will respond to environmental changes.     

Effects on water chemistry after drainage of a bog for forestry

Drainage for forestry has received increasing interest during recent decades. Generally, drainage concerns wet mineral soils while the utilization of peatlands is a matter of controversy. The peatlands mainly involved are fens, while forestry on bogs is an insignificant activity. Consequently, hydrology of bogs and effects of drainage on their hydrochemistry are little known.The investigation performed aimed at elucidating the parent conditions and the drainage impact on the hydrology and hydrochemistry of an ombrotrophic bog. Two bogs were first compared during a calibration period of two years and then, after drainage of one of them, during a period of three years. The second bog was kept virgin as a control.Considerable influences on runoff and stream water quality were found from the surrounding mineral soil uplands of the bog. Significant differences occurred between the chemical composition of the groundwater in the mineral soil and in the bog peat.Effects on runoff water from drainage of the bog deviate from drainage of minerotrophic peatlands with respect to decreased concentrations and losses of organic carbon and nitrogen. From two small bog catchments within the drained bog, there generally were greater losses of nutrients than from the catchment as a whole. Furthermore, the runoff from the drained bog decreased in comparison with the undrained condition. However, there were also similarities to drainage of other peatlands as regards increased pH, alkalinity and concentrations of sulphate. Also, concentrations of total-phosphorus increased in spite of a decreased phosphate (MRP) concentration.     

Plant community dynamics, nutrient cycling, and alternative stable equilibria in peatlands

Although observational data and experiments suggest that carbon flux and storage in peatlands are controlled by hydrology and/or nutrient availability, we lack a rigorous theory to account for the roles that different plant species or life-forms, particularly mosses, play in carbon and nutrient flux and storage and how they interact with different hydrologic sources of nutrients. We construct and analyze a model of peatlands that sheds some light on this problem. The model is a set of six coupled differential equations that define the flow of nutrients from moss and vascular plants to their litters, then to peat, and finally to an inorganic nutrient resource pool. We first analyze a simple version of this model (model 1) in which all nutrient input is from precipitation and enters the moss compartment directly, mimicking the dynamics of ombrotrophic bogs. There is a transcritical bifurcation that results in a switch of stability between two equilibrium bog communities: a moss monoculture and a community where mosses and vascular plants coexist. The bifurcation depends on the magnitudes of the input/output budget of the peatland and the life-history traits of the plants. We generalize model 1 to model 2 by dividing nutrient inputs between precipitation and groundwater, thus also allowing the development of minerotrophic fens that receive nutrient subsidies from both groundwater and precipitation and adding intraspecific competition (self-limitation) terms for both moss and vascular plants. Partitioning precipitation inputs between moss and the nutrient pool resulted in the greatest changes in model behavior, including the appearance of a lake and a vascular plant monoculture as well as the moss monoculture and coexistence equilibrium. As with model 1, these solutions are separated by transcritical bifurcations depending on critical combinations of parameters determining the input-output budget of the peatland as well as the life-history characteristics of the plant species. Model 2 also allowed for an early transient spike in vascular plant dominance followed by approach to near moss monoculture and then eventual approach to coexistence equilibrium. This generalized model mimics the broad features of successional development of peatlands from fens to bogs often found in the paleorecords of peat cores.     

Phylogenetic composition of bacterial communities in small boreal lakes and ombrotrophic bogs of the upper Volga basin

Fluorescent in situ hybridization (FISH) with rRNA-specific oligonucleotide probes was used to assess the numbers and phylogenetic diversity of prokaryotic microorganisms in the water of small boreal lakes and peatland catchments of the swampy upper Volga basin. The abundance of bacterioplankton in lake water was found to vary from 1.6 to 8.7 × 10⁶ cells ml⁻¹, with the highest values detected in neutral eutrophic lakes. The total cell numbers in the peat of ombrotrophic bogs were 3.9–4.3 × 10⁸ cells g⁻¹ of wet peat. The proportion of bacteria identified by the group-specific probes decreased from 79–85% in neutral (pH 6.6–6.9) mesotrophic and eutrophic lakes to 65–69% in acidic (pH 4.4–5.5) dystrophic lakes and to 51–58% in the peat of acidic (pH 3.6–3.9) ombrotrophic bogs. The diversity of bacterial communities was highest in lakes with neutral water. These communities were dominated by members of the phylum Actinobacteria (31–44% of the total bacterial number), while the contribution of Alphaproteobacteria (16–19%), Bacteroidetes (6–16%), Betaproteobacteria (6–7%), Planctomycetes (2–8%), and Gammaproteobacteria (4–5%) was also significant. In acidic dystrophic lakes, Actinobacteria (25–35%) and Betaproteobacteria (25–34%) predominated, while peatland catchments were dominated by the Alphaproteobacteria (20–23%). The presence of acidobacteria and some planctomycetes common for bogs in the water of acidic dystrophic lakes, as well as the high proportion of bacteria (31–49%) that were not identified by the group-specific probes, suggest the impact of microbial processes in peatland catchments on the microbial composition of the receiving waters.     

Bacterial populations and environmental factors controlling cellulose degradation in an acidic Sphagnum peat

Northern peatlands represent a major global carbon store harbouring approximately one-third of the global reserves of soil organic carbon. A large proportion of these peatlands consists of acidic Sphagnum-dominated ombrotrophic bogs, which are characterized by extremely low rates of plant debris decomposition. The degradation of cellulose, the major component of Sphagnum-derived litter, was monitored in long-term incubation experiments with acidic (pH 4.0) peat extracts. This process was almost undetectable at 10°C and occurred at low rates at 20°C, while it was significantly accelerated at both temperature regimes by the addition of available nitrogen. Cellulose breakdown was only partially inhibited in the presence of cycloheximide, suggesting that bacteria participated in this process. We aimed to identify these bacteria by a combination of molecular and cultivation approaches and to determine the factors that limit their activity in situ. The indigenous bacterial community in peat was dominated by Alphaproteobacteria and Acidobacteria. The addition of cellulose induced a clear shift in the community structure towards an increase in the relative abundance of the Bacteroidetes. Increasing temperature and nitrogen availability resulted in a selective development of bacteria phylogenetically related to Cytophaga hutchinsonii (94-95% 16S rRNA gene sequence similarity), which densely colonized microfibrils of cellulose. Among isolates obtained from this community only some subdivision 1 Acidobacteria were capable of degrading cellulose, albeit at a very slow rate. These Acidobacteria represent indigenous cellulolytic members of the microbial community in acidic peat and are easily out-competed by Cytophaga-like bacteria under conditions of increased nitrogen availability. Members of the phylum Firmicutes, known to be key players in cellulose degradation in neutral habitats, were not detected in the cellulolytic community enriched at low pH.     

Gradients of continentality and moisture in South Patagonian ombrotrophic peatland vegetation

This study presents the analysis of 381 phytosociological relevés describing predominantly ombrotrophic South Patagonian lowland peatland vegetation along a gradient of increasing continentality. Numerical methods such as cluster analysis and detrended correspondence analysis (DCA) were carried out to explore the data set. Cluster analysis resulted in nine vegetation types that were also distinctly separated in DCA ordination. The major floristic coenocline along the first DCA axis reflected a gradient of continentality ranging from pacific blanket bogs dominated by cushion plants toSphagnum-dominated continental raised bogs. Increasing continentality along the first axis was parallel with decreasing peat decomposition and increasing peat depth and acidity. In contrast, floristic variation along the second DCA axis represented a water level gradient. The typical sequence of vegetation types along the hollow-hummock moisture gradient that is well established for north hemispherical peatlands could also be observed inSphagnum-dominated South Patagonian raised bogs with a surprising similarity in floristic and structural features. Concerning the gradient of continentality significant differences in comparison with the northern hemisphere could be established. Most obvious was the dominance of cushion building plants (e.g.Astelia pumila, Donatia fascicularis) in South Patagonian oceanic peatlands, whereas this life form is totally absent from the northern hemisphere. Similar to the continentalSphagnum bogs the cushion plant vegetation of hyperoceanic peatlands exhibited a clear separation along the moisture gradient.     

Vegetation of Sphagnum bogs in highly disturbed landscapes: relative influence of abiotic and anthropogenic factors

Question: Has the vegetation of Sphagnum bogs been affected by more than 200 years of human activities? Location: Bas‐Saint‐Laurent region, southeastern Québec, Canada. Methods: Data (species assemblages, abiotic and spatio‐historical variables) were collected in 16 bogs ranging from 2 to 189 ha, and incorporated in a geographical information system. Major gradients in vegetation composition were identified using DCA. CCA was used to relate vegetation gradients to abiotic and spatio‐historical variables. Results: A clear segregation of species assemblages was observed, from open and undisturbed bogs to forested and highly disturbed sites. Among abiotic factors, tree basal area, water table level and peat thickness had a significant influence on plant species composition. Among spatio‐historical factors, disturbance level, area loss and fire were the most influential factors. Variance partitioning between these groups of factors suggests that spatio‐historical factors had a major influence on peatlands, representing 22% of the variation observed in the plant species assemblages while abiotic factors represent only 17% of the variation. Conclusions: The results highlight the influence of agricultural and other anthropogenic activities on plant assemblages and suggest that even wetlands apparently resistant to disturbances, such as peatlands, can be severely affected by anthropogenic factors. Plant species assemblages of ombrotrophic peatlands of the Bas‐Saint‐Laurent region were, and still are, largely influenced by human activities.     

Genes and genome-resolved metagenomics reveal the microbial functional make up of Amazon peatlands under geochemical gradients

The Pastaza-Marañón Foreland Basin (PMFB) holds the most extensive tropical peatland area in South America. PMFB peatlands store ~7.07 Gt of organic carbon interacting with multiple microbial heterotrophic, methanogenic, and other aerobic/anaerobic respirations. Little is understood about the contribution of distinct microbial community members inhabiting tropical peatlands. Here, we studied the metagenomes of three geochemically distinct peatlands spanning minerotrophic, mixed, and ombrotrophic conditions. Using gene- and genome-centric approaches, we evaluate the functional potential of the underlying microbial communities. Abundance analyses show significant differences in C, N, P, and S acquisition genes. Furthermore, community interactions mediated by toxin–antitoxin and CRISPR-Cas systems were enriched in oligotrophic soils, suggesting that non-metabolic interactions may exert additional controls in low-nutrient environments. Additionally, we reconstructed 519 metagenome-assembled genomes spanning 28 phyla. Our analyses detail key differences across the geochemical gradient in the predicted microbial populations involved in degradation of organic matter, and the cycling of N and S. Notably, we observed differences in the nitric oxide (NO) reduction strategies between sites with high and low N₂O fluxes and found phyla putatively capable of both NO and sulfate reduction. Our findings detail how gene abundances and microbial populations are influenced by geochemical differences in tropical peatlands.     

Cotton-Grass and Blueberry have Opposite Effect on Peat Characteristics and Nutrient Transformation in Peatland

Peatlands are large repositories of carbon (C). Sphagnum mosses play a key role in C sequestration, whereas the presence of vascular plants is generally thought to stimulate peat decomposition. Recent studies stress the importance of plant species for peat quality and soil microbial activity. Thus, learning about specific plant–microbe–soil relations and their potential feedbacks for C and nutrient cycling are important for a correct understanding of C sequestration in peatlands and its potential shift associated with vegetation change. We studied how the long-term presence of blueberry and cotton-grass, the main vascular dominants of spruce swamp forests, is reflected in the peat characteristics, soil microbial biomass and activities, and the possible implications of their spread for nutrient cycling and C storage in these systems. We showed that the potential effect of vascular plants on ecosystem functioning is species specific and need not necessarily result in increased organic matter decomposition. Although the presence of blueberry enhanced phosphorus availability, soil microbial biomass and the activities of C-acquiring enzymes, cotton-grass strongly depleted phosphorus and nitrogen from the peat. The harsh conditions and prevailing anoxia retarded the decomposition of cotton-grass litter and caused no significant enhancement in microbial biomass and exoenzymatic activity. Therefore, the spread of blueberry in peatlands may stimulate organic matter decomposition and negatively affect the C sequestration process, whereas the potential spread of cotton-grass would not likely change the functioning of peatlands as C sinks.     

Extremely short diapause in rotifers and its fitness consequences

Peatland pools usually show a marked gradient regarding their minerotrophic (harder and less acidic waters) versus ombrotrophic (softer and more acidic waters) status, which appears to be crucial in structuring their planktonic food webs. In this study, we analyzed the effect of such habitat diversity in shaping bacterioplankton assemblages. The planktonic bacteria from five pools located in Rancho Hambre peat bog (Tierra del Fuego Island) were studied through morphological and cytometric approaches, over more than one seasonal cycle. The community was always dominated by small cocci with an average cell size of 0.27 × 0.36 µm. Bacterioplankton morphological structure and cytometric fingerprint were correlated (Mantel test: P < 0.001), both methods used to characterize bacterioplankton showed significant differences between minero- and ombrotrophic pools. Variation in bacterial assemblage structure was mainly explained by abiotic variables relevant in peatlands such as pH, total hardness, conductivity, concentration of inorganic nutrients, and concentration and quality of dissolved organic carbon. Notably, these relatively fast approaches detected similar landscape-driven ecological patterns as previous high-throughput sequencing molecular studies of prokaryotes from the same pools, promising to be useful screening tools for limnological surveys as well as for monitoring the response of bacterial assemblages to environmental changes in peatland ecosystems.     

Seasonal variation in rates of methane production from peat of various botanical origins: effects of temperature and substrate quality

The methane produced in peat soils can vary over the growing season due to variations in the supply of available substrate, the activity of the microbial community or changes in temperature. Our aim was to study how these factors regulate the methane production over the season from five different peat types of different botanical origin. Peat samples were collected on seven occasions between June and September. After each sampling, the peat soils were incubated at five different temperatures (7, 10, 15, 20 and 25 degrees C) without added substrate, or at 20 degrees C with added substrate (glucose, or H(2)/CO(2), or starch). Rates of methane production averaged over the season differed significantly (P<0.05, R(2)=0.76) among the five peat types, the minerotrophic lawn producing the highest rates, and the hummock peat producing the lowest. The seasonal average Q(10) values for each plant community varied between 4.6 and 9.2, the highest value being associated with the ombrotrophic lawn and the lowest value with the mud-bottom plant community. For the unamended peat samples, the rates of methane production from each plant community varied significantly (P<0.05) over the season. This implies that the quality of organic matter, in combination with changes in temperature, explains the seasonal variation in methane production. However, addition of saturating amounts of glucose, H(2)/CO(2) or starch at 20 degrees C significantly reduced the seasonal variation (P<0.05) in methane production in peat from the minerotrophic lawn, wet carpet and mud-bottom plant communities. This suggests that substrate supply (e.g. root exudates) for the micro-organisms also varied over the season at these sites. Seasonal variation in methane production rates was apparent in peat from the hummock and ombrotrophic lawn plant communities even after addition of substrates, suggesting that the active biomass of the anaerobic microbial populations at these sites was regulated by other factors than the ones studied.     

Nutrient Input and Carbon and Microbial Dynamics in an Ombrotrophic Bog

Slow rates of plant production and decomposition in ombrotrophic bogs are believed to be partially the result of low nutrient availability. To test the effect of nutrient availability on decomposition, carbon dioxide (CO₂) flux dynamics, microbial biomass, and nutrients, we added nitrogen (N) with phosphorus (P) and potassium (K), to prevent limitation of the latter 2 nutrients, over 2 growing seasons to plots at Mer Bleue peatland, Ontario, Canada. After the first growing season, increasing N fertilization (with constant P and K) decreased in vitro CO₂ production potential and increased microbial biomass measured with a chloroform fumigation-extraction technique in the upper peat profile, while by the end of the second season, CO₂ production potential was increased in response to N plus PK treatment, presumably due to more easily decomposable newly formed plant material. In situ CO₂ fluxes measured using chamber-techniques over the second year corroborated this presumption, with greater photosynthetic CO₂ uptake and ecosystem respiration (ER) during high N plus PK treatments. The more efficient microbial community, with slower CO₂ production potential and larger biomass, after the first year was characterized by larger fungal biomass measured with signature phospholipid fatty acids. The majority of N was likely quickly sequestered by the vegetation and transferred to dissolved organic forms and microbial biomass in the upper parts of the peat profile, while additional P relative to controls was distributed throughout the profile, implying that the vegetation at the site was N limited. However, in situ CO₂ flux data suggested the possibility of P or NPK limitation. We hypothesize that nutrient deposition may lead to enhanced C uptake by altering the microbial community and decomposition, however this pattern disappears through subsequent changes in the vegetation and production of more readily decomposable plant tissues.     

Bacterial Communities of Regressive Spots in Ombrotrophic Bogs: Structure and Functions

Microbiology - This research analyses the structure and functions of bacterial communities of regressive spots in ombrotrophic bogs. Algal biomass was found to predominate in the biomass structure...     

Environmental factors explaining the vegetation patterns in a temperate peatland

Although ombrotrophic temperate peatlands are important ecosystems for maintaining biodiversity in eastern North America, the environmental factors influencing their flora are only partly understood. The relationships between plant species distribution and environmental factors were thus studied within the oldest temperate peatland of Québec. Plant assemblages were identified by cluster analysis while CCA was used to related vegetation gradients to environmental factors. Five assemblages were identified; three typical of open bog and two characterized by more minerotrophic vegetation. Thicker peat deposit was encounter underlying the bog assemblages while higher water table level and percentage of free surface water distinguished the minerotrophic assemblages. Overall, the floristic patterns observed were spatially structured along the margins and the expanse. The most important environmental factors explaining this spatial gradient were the percentage of free surface water and the highest water-table level. To cite this article: S. Pellerin et al., C. R. Biologies 332 (2009).     

Moorland pools as refugia for endangered species characteristic of raised bog gradients

In intact raised bog landscapes transitions from ombrotrophic into minerotrophic conditions occur. These gradients are lost from many bogs due to peat harvesting and drainage, and are difficult to restore. To determine which endangered species are characteristic of pristine raised bog gradients and their current status in degraded bogs, plants and macroinvertebrates were surveyed in Estonian intact raised bogs and Dutch degraded bog remnants. Dutch national distribution data were used to determine whether communities with these species occurred outside bog habitats. Water chemistry data were used to describe associated environmental conditions. Intact bog gradients were the preferred habitat for six plant species and fifteen macroinvertebrate species, all of which are endangered. In degraded bogs these species were scarce or not recorded. In intact bogs these species lived at sites where runoff from the bog massif came into contact with regional ground water resulting in a gradient in pH, alkalinity, Ca, Fe and ionic ratio. Analysis of Dutch national distribution data revealed aggregations of these endangered species in moorland pools. These pools contained water chemistry gradients similar to those found in pristine bogs, which occurred at sites were groundwater seepage and stream water came in contact. In the past, stream water has been used to increase pH and trophic status of moorland pools facilitating fisheries. Today, this practice offers a conservation strategy for the protection of endangered species for which no short-term alternatives are available.