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Aims: Peatland porewaters frequently contain large concentrations of dissolved organic nitrogen (DON), but small concentrations of inorganic N (NH4+ and NO3−). Our aim was to test whether peatland plants, with low tissue N concentrations (0.7 to 1.7%), have the ability to take up organic forms of N, specifically glycine.Methods: We applied dual-labeled (13C and 15N) glycine to two peatlands: an ombrotrophic bog in eastern Canada and a New Zealand restiad bog undergoing restoration. We compared the δ13C and δ15N values of control and treated above and below-ground plant tissues to establish whether the glycine had been taken up.Results: At the Canadian bog, the moss, shrub and sedge species treated with glycine showed significant increases in δ15N, above and below-ground, and there was evidence of a significant change in δ13C in shrub roots. At the New Zealand peatland, above- and below-ground tissues of the two restiad species and the roots of the sedge species showed significantly increased δ15N, while only the sedge roots showed a significant increase in δ13C.Conclusions: All but one of the nine plant species examined showed significant uptake of 15N in foliage and all roots showed increases in 15N. Variations in uptake appear to be partially related to the plant type and root characteristics. Large variations in C, 13C, N and 15N concentration within treatments precluded strong evidence of whether uptake included intact glycine. [ABSTRACT FROM AUTHOR]

The fruticose lichens Cladina stellaris and Cladina rangiferina, form thick mats that can cover large areas of northern peatlands (above c. 50° latitude), including the extensive peatlands of the Hudson Bay Lowland (HBL) in Canada, where lichens may cover up to 50% of the landscape. Despite the abundance of lichens in northern peatlands, our understanding of their role within peatland ecosystems, and peat accumulation in particular, is limited.We investigate the potential effect of these mat‐forming lichens on peat production and decomposition processes, using field data from an ombrogenous bog in the HBL and laboratory analyses. We hypothesize that (a) production in lichen‐shrub hummocks is less than in Sphagnum‐shrub hummocks; (b) the decay of lichen litter is faster than that of Sphagnum moss, so the mass litter input to the peat profile is reduced; and (c) faster decomposition of the underlying peat is stimulated by lichen leachates, resulting in greater mass loss.We found that thick lichen mats alter vegetation composition in peatlands, reducing Sphagnum cover and inhibiting the growth of small shrubs. Coupled with low lichen productivity that is constrained by moisture conditions, production for lichen‐shrub hummocks is significantly smaller than for Sphagnum‐shrub hummocks, confirming hypothesis (a). Our data also support hypothesis (b), with chemical analyses of lichen mats and leachates from lichen mats indicating faster decay of lichens compared to Sphagnum moss, and therefore reduced mass litter input to the peat profile in lichen‐dominated hummocks. Although we found no evidence to suggest leachates from lichens enhance decomposition processes in peatlands (hypothesis c), larger dry bulk densities for peat under lichen mats indicate a loss of structural integrity and potential collapse of the peat column.Synthesis. As production of new material added to the peat column is less in lichen‐dominated hummocks, local peat accumulation slows or ceases, representing a potential temporary limit to peat growth. Our results highlight the importance of lichens as a vegetation feedback in peatland development, with thick mats probably constraining or reducing hummock height relative to adjacent, lichen‐free hollows. Our findings highlight the importance of lichens as a vegetation feedback in the development of northern peatlands. In lichen‐dominated hummocks, production of new material added to the peat column is less, causing local peat accumulation to slow or cease. This represents a temporary limit to peat growth, with thick lichen mats probably constraining or reducing hummock height relative to adjacent, lichen‐free hollows. [ABSTRACT FROM AUTHOR]

Nutrient availability is an important control on the vegetation distribution, productivity and functioning of peatland ecosystems and we examined spatial and temporal patterns of nutrient availability through ion exchange at Mer Bleue bog, southeast Ontario, Canada. We installed ion exchange probes at 5–15 cm for 4 weeks and determined nutrient sorption at undisturbed sites as well as those affected by nitrogen (N), phosphorus (P), potassium (K) fertilization and drainage. Under undisturbed conditions, the bog had very small amount of available nutrients, especially N (ammonium > nitrate) and P, and exhibited small variations in nutrient availability during the growing season (May to October). The increase in NPK availability upon fertilization was short-lived over the season and the stoichiometry of available NPK captured by the probes was mismatched with the vegetation. The increase in nutrient availability with drainage was confounded by substantial changes in vegetation. We compare these results with data from other Canadian bogs and fens to provide baseline data on nutrient availability in peatlands. [ABSTRACT FROM AUTHOR]

Determining the plant traits that best predict carbon (C) storage is increasingly important as global change drivers will affect plant species composition and ecosystem C cycling. Despite the critical role of peatlands in the global C cycle, trait-flux relationships in peatlands are relatively unknown., We assessed the ability of four non-destructive plant traits to predict carbon dioxide ( CO2) and methane ( CH4) fluxes over two growing seasons in a temperate peatland in Ontario, Canada. We examined relationships between C-fluxes and leaf area, leaf persistence (deciduous, evergreen), growth form (woody, herbaceous) and aerenchyma tissue. To explore potential inconsistencies between different scales of data aggregation, traits were analysed at the level of plots, species and microsites., CO2 fluxes showed a positive relationship with leaf area and leaf persistence, and a negative relationship with proportion of woody species. CH4 fluxes showed a positive relationship with aerenchyma and leaf area. The significance of trait-flux relationships differed based on whether data were averaged at the level of plot, species or microsite., We recommend applying leaf area as a non-destructive trait to other systems where it is not ideal to measure traits destructively. A better understanding of the relationships between above and below-ground traits is likely needed to further explain variation in ecosystem respiration and CH4 fluxes from plant traits., A is available for this article. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) plays a key role in the peatland carbon balance and serves numerous ecological and chemical functions including acting as a microbial substrate. In this study, we quantify the concentration, biodegradability, and intrinsic properties of DOC obtained from peat, fresh material, and litter from nine species of ombrotrophic bog vegetation. Potential biodegradability was assessed by incubating vegetation extracts for 28 days in the dark and measuring percent DOC loss as the fraction of biodegradable DOC (%BDOC) while DOC properties were characterized using UV-Vis absorbance and fluorescence measurements. The mean initial DOC concentration extracted differed significantly among species ( P < 0.05) and was significantly higher in fresh material, 217 ± 259 mg DOC l, than either litter or peat extracts with mean concentrations of 82.1 ± 117 mg DOC l and 12.7 ± 1.0 mg DOC l, respectively ( P < 0.05). %BDOC also differed significantly among species ( P < 0.05) and ranged from 52 to 73% in fresh cuttings with the greatest fraction observed in S. magellanicum; 22-46% in litter; and 24% in peat. The majority of variability (82.5%) in BDOC was explained by initial absorbance at 254 nm and total dissolved nitrogen concentration which was further resolved into significant non-linear relationships between %BDOC and both humic-like and protein-like DOC fractions ( P < 0.05). Our results highlight the extremely heterogeneous nature of the surface vegetation-derived DOC input in peatlands and stress the importance of vegetation species in peatland ecosystem function. [ABSTRACT FROM AUTHOR]

Ombrotrophic bogs are nutrient-poor systems and important carbon (C) sinks yet there remains a dearth of information on the belowground stoichiometry of C, nitrogen (N), phosphorus (P), and potassium (K), important determinants of substrate quality for microorganisms, in these systems. In this study, we quantified the C, N, P, and K concentrations of both hummock peat and dissolved matter as well as microbial extracellular enzyme activity from 0 to 10 cm depth in the long-term NPK fertilization plots at Mer Bleue bog. Greater N-loading resulted in significantly reduced C:N and greater C:P and C:K ( p < 0.05) while the addition of NPK resulted in significantly lower C:P and C:K ( p < 0.05) and lower C:N relative to N-only treatments but the difference in C:N was not significant ( p > 0.05). Hydrolase enzyme activity followed resource allocation models with significantly suppressed N-acetyl- β- d-glucosaminidase and phosphatase activity ( p < 0.05) and enhanced β- d-glucosidase activity with greater N- and P-availability. The concentration of inhibitory phenolics was significantly greater with N-loading ( p < 0.05), due in part to shifts in surface vegetation, while phenol oxidase activity was significantly suppressed by N ( p < 0.05) with results suggesting greater suppression by NH than NO . Taken together, these results suggest that higher levels of nutrients impact both microbial substrate quality as well as the activity of microbial enzymes that are key to the decomposition process that may ultimately decrease carbon sequestration in bogs. [ABSTRACT FROM AUTHOR]

The large accumulation of carbon in peatlands arises from slow organic matter decomposition where microorganisms and their enzyme activities play a critical role. However, there is a dearth of studies on the natural patterns of peatland microbial enzyme activity and inhibitory phenolic compounds over seasons, and across a range of depths and biogeochemically different peatland types. We report the spatiotemporal patterns for phenol oxidases, phenolics, and a suite of five key hydrolase enzymes at two depths in two ombrotrophic bogs, mineral poor and rich fens, and a forested basin swamp over the growing season. Results obtained using linear fixed and mixed effect models suggest that phenol oxidase activity varies significantly with temperature and, to a lesser extent pH, leading to a breakdown of inhibitory phenolics and increased hydrolase enzyme activity across all peatland types. Overall, enzyme activity decreased significantly with depth and showed significant variation over the course of the growing season with a minimum in the spring and a maximum in the summer and fall. Enzyme activities were generally greatest in the rich fen and lowest in the forested basin swamp with no significant difference between bogs and poor fens. Site-specific factors such as nutrient availability explain deviations from these patterns. Our results illustrate the widespread but conditional applicability of the enzyme-latch mechanism to peatlands and the vulnerability of the peatland soil organic carbon stock to climate warming. [ABSTRACT FROM AUTHOR]

The Mer Bleue peatland is a large ombrotrophic bog with hummock-lawn microtopography, poor fen sections and beaver ponds at the margin. Average growing-season (May-October) fluxes of methane (CH) measured in 2002-2003 across the bog ranged from less than 5 mg m d in hummocks, to greater than 100 mg m d in lawns and ponds. The average position of the water table explained about half of the variation in the season average CH fluxes, similar to that observed in many other peatlands in Canada and elsewhere. The flux varied most when the water table position ranged between −15 and −40 cm. To better establish the factors that influence this variability, we measured CH flux at approximately weekly intervals from May to November for 5 years (2004-2008) at 12 collars representing the water table and vegetation variations typical of the peatland. Over the snow-free season, peat temperature is the dominant correlate and the difference among the collars' seasonal average CH flux is partially dependent on water table position. A third important correlate on CH flux is vegetation, particularly the presence of Eriophorum vaginatum, which increases CH flux, as well as differences in the potential of the peat profile to produce and consume CH under anaerobic and aerobic conditions. The combination of peat temperature and water table position with vegetation cover was able to explain approximately 44% of the variation in daily CH flux, based on 1097 individual measurements. There was considerable inter-annual variation in fluxes, associated with varying peat thermal and water table regimes in response to variations in weather, but also by variations in the water level in peripheral ponds, associated with beaver dam activity. Raised water level in the beaver ponds led to higher water tables and increased CH emission in the peatland. [ABSTRACT FROM AUTHOR]

The large accumulation of organic matter in peatlands has been partially attributed to litter decomposition rates, which are slowed by a high water table. To test this, we examined whether there were significant differences in the decomposition and N and P dynamics of ten foliar litters and wood blocks at three pairs of upland forest and peatland sites in the transitional grassland, high boreal and low subarctic regions of central Canada, using litterbags collected over a 12-year period. At two of the three pairs, the decomposition rate, as determined by proportion of the original mass remaining after 12 years and by the exponential decay coefficient ( k), was faster overall at the upland than at the peatland. In the third pair, there was no significant difference, despite the water table being close to the peat surface; warmer soil temperatures in the peatland than the upland may be the cause. In general, there were small losses or gains of N in the litters after 12 years, compared to the original litter, though there were some differences among litter types and sites, net gains in N likely reflecting the higher exogenous N availability. P was lost from most litters at the two northern pairs of sites, but at the transitional grassland pair, there were large net gains in P and greater variation among litters. The N:P ratio in the original litters ranged from 5 to 26 and after 12 years the ratio narrowed, with the site average of the ten litters ranging from 13 to 22, varying with the soil ratio. Decomposition rates and N and P dynamics after 12 years are different between upland and peatland sites: although the water table is a primary control on these differences, other factors such as temperature and soil nutrient status are also important. [ABSTRACT FROM AUTHOR]

The large accumulation of organic matter in peatlands is primarily caused by slow rates of litter decomposition. We determined rates of decomposition of major peat-forming litters of vascular plants and mosses at five sites: a poor fen in New Hampshire and a bog hummock, a poor fen, a beaver pond margin and a beaver pond in Ontario. We used the litterbag technique, retrieving triplicate litterbags six or seven times over 3–5 years, and found that simple exponential decay and continuous-quality non-linear regression models could adequately characterize the decomposition in most cases. Within each site, the rate of decomposition at the surface was generally Typha latifolia leaves = Chamaedaphne calyculata leaves = Carex leaves > Chamaedaphne calyculata stems > hummock Sphagnum = lawn/hollow Sphagnum, with exponential decay constant ( k) values generally ranging from 0.05 to 0.37 and continuous-quality model initial quality ( q 0 ) values ranging from 1.0 (arbitrarily set for Typha leaves) to 0.7 ( Sphagnum). In general, surface decay rates were slowest at the bog hummock site, which had the lowest water table, and in the beaver pond, which was inundated, and fastest at the fens. The continuous-quality model site decomposition parameter ( u 0 ) ranged from 0.80 to 0.17. Analysis of original litter samples for carbon, nitrogen and proximate fractions revealed a relatively poor explanation of decomposition rates, as defined by k and q 0 , compared to most well-drained ecosystems. Three litters, roots of sedge and a shrub and Typha leaves, were placed at depths of 10, 30 and 60 cm at the sites. Decomposition rates decreased with depth at each site, with k means of 0.15, 0.08 and 0.05 y−1 at 10, 30 and 60 cm, respectively, and u 0 of 0.25, 0.13 and 0.07. These differences are primarily related to the position of the water table at each site and to a lesser extent the cooler temperatures in the lower layers of the peat. The distinction between bog and fen was less important than the position of the water table. These results show that we can characterize decomposition rates of surface litter in northern peatlands, but given the large primary productivity below-ground in these ecosystems, and the differential rates of decomposition with depth, subsurface input and decomposition of organic matter is an important and relatively uncertain attribute. [ABSTRACT FROM AUTHOR]

The article presents a study that determines the concentration of dissolve organic carbon (DOC) and the specific ultraviolet absorbance of 193 samples of water collected from groundwater, porewater, drainage ditches, and streams at peatlands in New Zealand. Results from the study shows that there was a wide range in DOC concentration in peatlands where there appeared to be large amount of iron. Also, DOC concentrations were large in ombrotrophic, or rain-fed peatlands.

In northern ecosystems, the onset and growth of spring photosynthesis may have an important influence on the annual carbon (C) budget, yet the controls have not been clearly identified, especially for peatlands. We used a 5-year set of daily carbon dioxide (CO2) exchange measurements derived from an eddy covariance tower located at Mer Bleue, an ombrotrophic bog near Ottawa, Canada, from March to May [day-of-year (DOY) 60–150], 1999–2003. We used half-hourly measured net ecosystem exchange minus modelled ecosystem respiration to estimate daily photosynthesis, as gross ecosystem production (GEP). The onset of GEP in each year was closely related to the thinning and disappearance of the snow cover, occurring between DOY 86 and 101. GEP increased during the spring, reaching 10-day average values of between 5 and 9 g CO2 m−2 day−1 by the end of May. This increase was initially associated with moss activity ( Sphagnum and Polytrichum), followed by the evergreen shrubs. Peat temperatures in the rooting zone (10–20 cm depth) and increases in shrub leaf nitrogen and chlorophyll a concentrations contributed to this rapid increase in GEP. Examination of moderate-resolution imaging spectroradiometer (MODIS) images over several years revealed that the temporal resolution (16-day composites) was inadequate to capture the onset of GEP but estimates of gross primary productivity and photosynthesis from MODIS 8-day composites for the most part followed the pattern and magnitude of CO2 exchange observed at the tower. [ABSTRACT FROM AUTHOR]

Carbon (C) modeling and carbon dioxide (CO2) flux measurements in peatlands are dependent on the distribution and productivity of vegetation in a system with a high degree of spatial variability, often linked to the position of the water table. We tested the hypothesis that at a fine-scale (tens of metres) water table position exerts a strong control on species abundance, plant biomass, particularly photosynthetically active tissues, leaf area index (LAI), and areal foliar N and chlorophyll at Mer Bleue, a cool temperate peatland in eastern Canada. Total aboveground biomass ranged from 147 to 1011 g·m–2, with shrubs contributing between 42% and 72% of the total in the transects. We found significant (P < 0.05) positive relationships between foliar and total vascular plant biomass and mean water table position, and significant decreases in the shrub foliar:woody biomass ratio and moss biomass with a lower water table. However, there was no significant relationship between water table position and photosynthetically active tissues (vascular plant leaves and moss capitulum), ranging from 114 to 672 g·m–2) and the areal mass of N in these tissues, ranging from 1.5 to 6.7 g·m–2. Multivariate analyses of vegetation and environmental data showed that species distribution could be explained by both water table and chemistry gradients and that unimodal rather than linear responses best described the species and water table relationships. LAI ranged from 0.1 to over 3 and was correlated with both water table position and with vascular foliar biomass. Percent cover of shrubs was correlated with foliar biomass and LAI. Our results suggest that the less labour-intensive estimates of percent cover can be used to predict the vascular plant foliar biomass and LAI measurements. The lack of relationship between photosynthetically active tissues, tissue N concentrations, and water table may also explain the surprising lack of spatial variability in peak growing season eddy flux net ecosystem CO2 exchange in three different areas of the peatland. [ABSTRACT FROM AUTHOR]

We investigated the response of CO2 and CH4 production to a water table fluctuation and a SO42− pulse in a bog mesocosm. Net gas production rates in the mesocosm were calculated from concentration data by diffusive mass-balances. Incubation experiments were used to quantify the effect of SO42− addition and the distribution of potential CO2 and CH4 production rates. Flooding of unsaturated peat resulted in rapid depletion of O2 and complex patterns of net CH4, CO2, and H2S production. Methane production began locally and without a time lag at rates of 3–4 nmol cm−3 d−1 deeper in the peat. Similar rates were determined after a time lag of 10–60 days in the surface layers, whereas rates at lower depths declined. Net CO2 production was largest immediately after the water table position was altered (100–300 nmol cm−3 d−1) and declined to −50–50 nmol cm−3 d−1 after a few weeks. SO42− addition (500 mM) significantly increased potential CH4 production rates in the surface layer from an average of 132–201 nmol cm−3 d−1 and reduced it below from an average of 418–256 nmol cm−3 d−1. Our results suggest that deeper in the peat (40–70 cm) under in situ conditions, methanogenic populations are less impaired by unsaturated conditions than in the surface layers, and that at these depths after flooding the substrate availability for CH4 and DIC production is significantly enhanced. They also suggest that methanogenic and SO42−-reducing activity were non-competitive in the surface layer, which might explain contradictory findings from field studies. [Copyright &y& Elsevier]

Peat deposits of the Muara Siran, East Kalimantan area, were investigated for their vertical and lateral succession, to examine the characteristic variability, particularly its macro- and microtextures. The deposits are situated in the Kutai Basin, in the vicinity of several Cenozoic coal deposits. Peat samples were taken from twenty-seven coring sites in the area, using a MacCaulay peat corer. The Muara Siran peatlands lie between the Kedang Kepala and Belayan Rivers. Siran Lake lies between these rivers and within the peat system. The peat thickness varied from 0.5 m to 12 m. Decomposed sapric peat formed the basal and margins of the deposit, overlain by moderatelydecomposed hemic peat in the central part of the peatlands, though both sapric and hemic peat types are interbedded at the margins of the mire. The fibric peat types were found mostly at the top of the mire and only distal from any active streams. Twenty-four samples of peat were freeze-dried for petrographic analyses of both plant part and maceral analyses using a reflected microscope. On the average, the dominant plant parts were stems and wood (i.e. secondary xylem). Maceral composition was mostly from the huminite group (on the average 89%), particularly the macerals humodetrinite and textinite. Macroscopic peat type and microscopic composition are linked. Fibric peat was found to be rich in wood and textinite. Hemic was mostly composed of stems and wood with textinite and humodetrinite as the most abundant macerals. Sapric peat has near equal proportions of stems, wood, and macerated tissue. Humodetrinite is the most abundant maceral in sapric. The average ash and sulfur content were low, 1.29 wt.% and 0.11 wt.%, respectively. Understanding the physical characteristics of inland peat as in Muara Siran peatland is essential to build knowledge of how inland peat is formed and what makes it different from coastal peat. Muara Siran is a unique, relatively small peatland in the central eastern Kalimantan which is still considerably pristine, hence may serve the aim of this study well. [ABSTRACT FROM AUTHOR]

Spatial surface patterns of hummocks, hollows, ridges, and pools (microtopography) are common features of many northern peatlands and are particularly distinct within the vast peatlands of the Hudson Bay Lowland (HBL), Canada. Hypotheses and models describe how small-scale feedbacks among vegetation, hydrology, and nutrients cause spatial differences in peat accumulation that enable microforms and surface patterns to develop over time. Empirical tests of the predictions from theoretical models of these proposed feedback mechanisms are limited, particularly in large peatland complexes such as the HBL. We investigate feedbacks controlling peatland structure and function in an ombrogenous bog and a minerogenous fen in the HBL. Our sites represent surface patterns found in many northern peatlands, specifically spatially irregular hummocks and hollows, and parallel ridges and pools that are perpendicular to slope. We found the occurrence of different spatial patterns depends on position within a peat landform, with these differences attributed to the ecohydrological setting. In turn, the ecohydrological setting, with different water table depths, nutrient availability, and species composition, influences the strength and direction of feedback mechanisms at the microform scale. Our data support the prediction of a positive feedback between plant productivity and acrotelm thickness for peat accumulation and hummock growth and that this may be enhanced by water ponding on slopes to form ridge–pool tracks. We did not find evidence to support the proposed feedback among evapotranspiration-driven transport of water and nutrients for the development of hummocks. Our results suggest a combination of mechanisms operating at various temporal and spatial scales is associated with the development of surface patterns in northern peatlands. [ABSTRACT FROM AUTHOR]

Pools are common in northern peatlands but studies have seldom focused on their nutrient biogeochemistry, especially in relation to their morphological characteristics and through seasons. We determined the environmental characteristics controlling carbon (C), nitrogen (N) and phosphorus (P) biogeochemistry in pools and assessed their evolution over the course of the 2016 growing season in a subboreal ombrotrophic peatland of eastern Canada. We showed that water chemistry variations in 62 pools were significantly explained by depth (81.9%) and the surrounding vegetation type (14.8%), but not by pool area or shape. Shallow pools had larger dissolved organic carbon (DOC) and total nitrogen (TN) concentrations and lower pH than deep pools, while pools surrounded by coniferous trees had more recalcitrant DOC than pools where vegetation was dominated by mosses. The influence of depth on pool biogeochemistry was confirmed by the seasonal survey of pools of different sizes with 47.1% of the variation in pool water chemistry over time significantly explained. Of this, 67.3% was explained by the interaction between time and pool size and 32.7% by pool size alone. P concentrations were small in all pools all summer long and combined with high N:P ratios, are indicative of P-limitation. Our results show that pool biogeochemistry is influenced by internal processes and highlight the spatial and temporal heterogeneity of nutrient biogeochemistry in ombrotrophic peatlands. [ABSTRACT FROM AUTHOR]

Hydrological disturbances can alter the structure and function of ecosystems by changing plant species composition over time. Peatlands in the northern hemisphere are particularly sensitive to global change drivers related to soil water availability, such as drought and drainage, because of important ecohydrological feedbacks between species composition and water table position. Here, we examined the plant community structure and environmental drivers of species distributions over two growing seasons along a bog – margin gradient, pre- and post-disturbance by beaver activity. Pond drainage resulted in seasonal average water table depth 8–24 cm lower in the second season. Five plant communities corresponded to changes in water table depth and acidity: bog, poor fen, meadow, mudflat and pond. Plant cover increased in meadow and mudflat communities, decreased in the pond community and did not differ between years in bog and poor fen communities. Changes in species abundance between years showed signs of alternate successional pathways: one that favors Sphagnum moss and bog community expansion and another pathway that favors meadow and mudflat expansion. This study highlights the non-linear successional trajectory of plant communities with changes in water table depth, which has implications for land management goals that aim to conserve the ecological integrity of peatland ecosystems. [ABSTRACT FROM AUTHOR]

Summary: Ericaceous shrubs adapt to the nutrient‐poor conditions in ombrotrophic peatlands by forming symbiotic associations with ericoid mycorrhizal (ERM) fungi. Increased nutrient availability may diminish the role of ERM pathways in shrub nutrient uptake, consequently altering the biogeochemical cycling within bogs.To explore the significance of ERM fungi in ombrotrophic peatlands, we developed the model MWMmic (a peat cohort‐based biogeochemical model) into MWMmic‐NP by explicitly incorporating plant‐soil nitrogen (N) and phosphorus (P) cycling and ERM fungi processes. The new model was applied to simulate the biogeochemical cycles in the Mer Bleue (MB) bog in Ontario, Canada, and their responses to fertilization.MWMmic_NP reproduced the carbon(C)–N–P cycles and vegetation dynamics observed in the MB bog, and their responses to fertilization. Our simulations showed that fertilization increased shrub biomass by reducing the C allocation to ERM fungi, subsequently suppressing the growth of underlying Sphagnum mosses, and decreasing the peatland C sequestration. Our species removal simulation further demonstrated that ERM fungi were key to maintaining the shrub–moss coexistence and C sink function of bogs.Our results suggest that ERM fungi play a significant role in the biogeochemical cycles in ombrotrophic peatlands and should be considered in future modeling efforts. See also the Commentary on this article by Barel & Robroek, 238: 5–7. [ABSTRACT FROM AUTHOR]

About 0.3 million km of boreal forests and peatlands and their soils have been flooded through the creation of hydroelectric reservoirs. To establish the effect of flooding on dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) production, we incubated six sample types of boreal forest and peatland soils and litters for 15 weeks under flooded (anoxic and suboxic) and non-flooded (oxic) conditions at three temperatures (4, 12, and 22 °C). Water was sampled at 3-week intervals and analyzed for DOC and TDN concentration. Cumulative DOC and TDN production ranged widely: from 4.4 to 146.2 mg C g C for DOC and 4.4 to 112.2 mg N g N for TDN under flooded conditions, and from 1.3 to 16.6 mg C g C for DOC and 0.7 to 8.5 mg N g N for TDN under non-flooded conditions. Cumulative DOC and TDN production was greater under flooded than non-flooded conditions for all sample types with flooded:non-flooded ratios averaging 10.6 for DOC and 9.5 for TDN. Within the flooded treatments, anoxic conditions produced more cumulative DOC and TDN than suboxic conditions, with average anoxic:suboxic ratios of 1.3 and 5.8 for DOC and TDN, respectively. Raising temperatures increased cumulative DOC and TDN production marginally under both flooded and non-flooded conditions as the average ratios for 22:12 and 12:4 °C were 1.1 for DOC and 1.2 for TDN. Generally, more DOC and TDN were released from litters than soils under both the flooded and non-flooded incubations, with litter:soil ratios averaging 8.5 for DOC and 2.1 for TDN. DOC:TDN ratio was generally higher in the solutions than in the original sample, particularly in the litters. This study thus indicated that DOC and TDN production was largely affected by flooding regime, O concentration, and substrate characteristics and less affected by temperature. [ABSTRACT FROM AUTHOR]

Peatlands both accumulate carbon and release methane, but their broad range in environmental conditions means that the diversity of microorganisms responsible for carbon cycling is still uncertain. Here, we describe a community analysis of methanogenic archaea responsible for methane production in 17 peatlands from 36 to 53 N latitude across the eastern half of North America, including three metal-contaminated sites. Methanogenic community structure was analysed through Illumina amplicon sequencing of the mcrA gene. Whether metal-contaminated sites were included or not, metal concentrations in peat were a primary driver of methanogenic community composition, particularly nickel, a trace element required in the F430 cofactor in methyl-coenzyme M reductase that is also toxic at high concentrations. Copper was also a strong predictor, likely due to inhibition at toxic levels and/or to cooccurrence with nickel, since copper enzymes are not known to be present in anaerobic archaea. The methanogenic groups Methanocellales and Methanosarcinales were prevalent in peatlands with low nickel concentrations, while Methanomicrobiales and Methanomassiliicoccales were abundant in peatlands with higher nickel concentrations. Results suggest that peat-associated trace metals are predictors of methanogenic communities in peatlands. [ABSTRACT FROM AUTHOR]

Information about the impact of nitrogen (N) deposition on the fate of deposited N in peatland ecosystems is lacking. Thus we investigated the fate of experimentally added N in long-term N-fertilized treatments in a Sphagnum-dominated ombrotrophic bog. Fertilization significantly stimulated vascular plant and suppressed Sphagnum and Polytrichum moss growth. N content in peat, mosses, and vascular plants was raised by the fertilizer addition and reached a maximum at 3.2 g m N input level with phosphorus (P) and potassium (K) addition. Most of N was retained in the vegetation and upper 10 cm of the peat. When N deposition equalled 1.6 g m and less, or 3.2 g m N with P and K addition, no inorganic N leaching was observed on the plots. This result indicates that co-fertilization with P and K raised the N retention capacity and that critical N loads with respect to N saturation depend on P and K availability. Most of the deposited N was recovered in the bulk peat, which may be related to a rapid immobilization of inorganic N by microorganisms and mycorrhizal assimilation. Increase of N, P, and K fertilization increased the contribution of vascular plants to N retention significantly and reduced those of mosses. The increase was mainly related to enhanced productivity, vascular biomass and N content in tissues; the reduced retention by mosses resulted from both reduced moss biomass and assimilation. The study shows that the N filter function of ombrotrophic bogs will be influenced by interactions with other nutrients and shifts in plant community structure. [ABSTRACT FROM AUTHOR]

Peatlands contain approximately 25% of the global soil carbon (C), despite covering only 3% of the earth's land surface. In order to evaluate the role of peatlands in global C cycling, models of ecosystem biogeochemistry are required, but peatland ecosystems present a number of unique challenges, particularly how to deal with the large variability that occurs at scales of one to several metres. In models, spatial variability is considered either explicitly for each individual unit and the outputs averaged, referred to as flux upscaling, or implicitly by weighting model parameters by the fractional occurrence of the individual units, referred to as parameter upscaling. The advantage of parameter upscaling is that it is much more computationally efficient: a requirement for hemispheric scale simulations. In this study we determined the differences between modelling a raised bog peatland with hummock–hollow microtopography using flux and parameter upscaling. We used the McGill Wetland Model (MWM), a process-based ecosystem C model for peatlands, configured for hummocks and hollows separately and then a weighted mixture of both. The simulated output based on flux and parameter upscaling was compared with eddy-covariance tower measurements. We found that net ecosystem production (NEP) for hollows was much larger than that for hummocks because total ecosystem respiration (TER) for hummocks was greater while gross primary production (GPP) did not differ significantly between the two topographic features. However, despite differences in components of NEP between hummocks and hollows, there was no statistically significant difference between the NEP based on flux and parameter upscaling using the MWM. Both flux and parameter upscaling show equivalent capability to capture the magnitude, direction, seasonality and inter-annual variability. The root-mean-square-errors (RMSE) are 0.66, 0.45, and 0.49gCm−2 day−1, respectively for GPP, TER and NEP based on the flux upscaling, while 0.67, 0.44, and 0.48gCm−2 day−1, respectively based on the parameter upscaling. The degree of agreement (d*) is 0.96, 0.97, and 0.88, respectively for GPP, TER and NEP based on the flux upscaling, while 0.96, 0.97, and 0.89, respectively based on the parameter upscaling. This result suggests that differences in processes caused by peatland microtopography scale linearly, which means an ecosystem-level model set-up (i.e. parameter upscaling scheme), is sufficient to simulate the C cycling. [Copyright &y& Elsevier]

nthropogenic nitrogen (N) loading has the potential to affect plant community structure and function, and the carbon dioxide (CO) sink of peatlands. Our aim is to study how vegetation changes, induced by nutrient input, affect the CO exchange of a nutrient-limited bog. We conducted 9- and 4-year fertilization experiments at Mer Bleue bog, where we applied N addition levels of 1.6, 3.2, and 6.4 g N m a, upon a background deposition of about 0.8 g N m a, with or without phosphorus and potassium (PK). Only the treatments 3.2 and 6.4 g N m a with PK significantly affected CO fluxes. These treatments shifted the Sphagnum moss and dwarf shrub community to taller dwarf shrub thickets without moss, and the CO responses depended on the phase of vegetation transition. Overall, compared to the large observed changes in the vegetation, the changes in CO fluxes were small. Following Sphagnum loss after 5 years, maximum ecosystem photosynthesis (Pg) and net CO exchange (NEE) were lowered (−19 and −46%, respectively) in the highest NPK treatment. In the following years, while shrub height increased, the vascular foliar biomass did not fully compensate for the loss of moss biomass; yet, by year 8 there were no significant differences in Pg and NEE between the nutrient and the control treatments. At the same time, an increase (24–32%) in ecosystem respiration (ER) became evident. Trends in the N-only experiment resembled those in the older NPK experiment by the fourth year. The increasing ER with increasing vascular plant and decreasing Sphagnum moss biomass across the experimental plots suggest that high N deposition may lessen the CO sink of a bog. [ABSTRACT FROM AUTHOR]

We studied the effect of long-term water table drawdown on the vascular plant community in an ombrotrophic bog in central Finland by measuring aboveground biomass and belowground production (by in-growth cores) across plant functional groups including herbs, shrubs, and trees. We compared drained and undrained portions 45 years after the installation of a drainage ditch network, which has lowered water levels of 15–20 cm on average in the drained part of the site. Although shrub fine root production did not differ significantly between sites, water table drawdown increased belowground tree fine root production by 740% (3.8 ± 5.4 SD and 28.1 ± 24.1 g m−2 y−1 in undrained and drained sites, respectively) at the expense of herb root production, which declined 38% (27.62 ± 16.40 and 10.58 ± 15.7 g m−2 y−1 in undrained and drained sites, respectively) yielding no significant overall change in total fine root production. Drainage effects on aboveground biomass showed a similar pattern among plant types, as aboveground tree biomass increased dramatically with drainage (79 ± 135 and 2546 ± 1551 g m−2 in drained and undrained sites, respectively). Although total shrub biomass was not significantly different between sites, shrubs allocated more biomass to stems than leaves in the drained site. Drainage also caused a significant shift in shrub species composition. Although trees dominated the aboveground biomass following water table drawdown, understorey vegetation, mainly shrubs, continued to dominate belowground fine root production, comprising 64% of total root production at the drained site. Aboveground biomass proved to be a good predictor of belowground production, suggesting that allometric relationships can be developed to estimate belowground production in these systems. Increase in tree root production can counteract decrease in herb fine root production following water table drawdown, emphasizing the importance of plant functional type responses to water table drawdown. Whether these changes will offset ecosystem C loss via increased plant C storage or stimulate soil organic matter decomposition via increased above- and belowground litter inputs requires further study. [ABSTRACT FROM AUTHOR]

Changes of water table position influence carbon cycling in peatlands, but effects on the sources and sinks of carbon are difficult to isolate and quantify in field investigations due to seasonal dynamics and covariance of variables. We thus investigated carbon fluxes and dissolved carbon production in peatland mesocosms from two acidic and oligotrophic peatlands under steady state conditions at two different water table positions. Exchange rates and CO2, CH4 and DOC production rates were simultaneously determined in the peat from diffusive-advective mass-balances of dissolved CO2, CH4 and DOC in the pore water. Incubation experiments were used to quantify potential CO2, CH4, and DOC production rates. The carbon turnover in the saturated peat was dominated by the production of DOC (10–15 mmol m-2 d-1) with lower rates of DIC (6.1–8.5 mmol m-2 d-1) and CH4 (2.2–4.2 mmol m-2 d-1) production. All production rates strongly decreased with depth indicating the importance of fresh plant tissue for dissolved C release. A lower water table decreased area based rates of photosynthesis (24–42%), CH4 production (factor 2.5–3.5) and emission, increased rates of soil respiration and microbial biomass C, and did not change DOC release. Due to the changes in process rates the C net balance of the mesocosms shifted by 36 mmol m-2 d-1. According to our estimates the change in C mineralization contributed most to this change. Anaerobic rates of CO2 production rates deeper in the peat increased significantly by a factor of 2–3.5 (DOC), 2.9–3.9 (CO2), and 3–14 (CH4) when the water table was lowered by 30 cm. This phenomenon might have been caused by easing an inhibiting effect by the accumulation of CO2 and CH4 when the water table was at the moss surface. [ABSTRACT FROM AUTHOR]

We measured net ecosystem exchange of carbon dioxide (CO2) (NEE) during wet and dry summers (2000 and 2001) across a range of plant communities at Mer Bleue, a large peatland near Ottawa, southern Ontario, Canada. Wetland types included ombrotrophic bog hummocks and hollows, mineral-poor fen, and beaver pond margins. NEE was significantly different among the sites in both years, but rates of gross photosynthesis did not vary spatially even though species composition at the sites was variable. Soil respiration rates were very different across sites and dominated interannual variability in summer NEE within sites. During the dry summer of 2001, net CO2 uptake was significantly smaller, and most locations switched from a net sink to a source of CO2 under a range of levels of photosynthetically active radiation (PAR). The wetter areas—poor fen and beaver pond margin—had the largest rates of CO2 uptake and smallest rates of respiratory loss during the dry summer. Communities dominated by ericaceous shrubs (bog sites) maintained similar rates of gross photosynthesis between years; by contrast, the sedge-dominated areas (fen sites) showed signs of early senescence under drought conditions. Water table position was the strongest control on respiration in the drier summer, whereas surface peat temperature explained most of the variability in the wetter summer. Q 10 temperature-respiration quotients averaged 1.6 to 2.2. The ratio between maximum photosynthesis and respiration ranged from 3.7:1 in the poor fen to 1.2:1 at some bog sites; it declined at all sites in the drier summer owing to greater respiration rates relative to photosynthesis in evergreen shrub sites and a change in both processes in sedge sites. Our ability to predict ecosystem responses to changing climate depends on a more complete understanding of the factors that control NEE across a range of peatland plant communities. [ABSTRACT FROM AUTHOR]

Peatlands are important players in climate change–biosphere feedbacks via long-term net carbon (C) accumulation in soil organic matter and as potential net C sources including the potent greenhouse gas methane (CH4). Interactions of climate, site-hydrology, plant community, and groundwater chemical factors influence peatland development and functioning, including C dioxide (CO2) and CH4 fluxes, but the role of microbial community composition is not well understood. To assess microbial functional and taxonomic dissimilarities, we used high throughput sequencing of the small subunit ribosomal DNA (SSU rDNA) to determine bacterial and archaeal community composition in soils from twenty North American peatlands. Targeted DNA metabarcoding showed that although Proteobacteria, Acidobacteria, and Actinobacteria were the dominant phyla on average, intermediate and rich fens hosted greater diversity and taxonomic richness, as well as an array of candidate phyla when compared with acidic and nutrient-poor poor fens and bogs. Moreover, pH was revealed to be the strongest predictor of microbial community structure across sites. Predictive metagenome content (PICRUSt) showed increases in specific genes, such as purine/pyrimidine and amino-acid metabolism in mid-latitude peatlands from 38 to 45° N, suggesting a shift toward utilization of microbial biomass over utilization of initial plant biomass in these microbial communities. Overall, there appears to be noticeable differences in community structure between peatland classes, as well as differences in microbial metabolic activity between latitudes. These findings are in line with a predicted increase in the decomposition and accelerated C turnover, and suggest that peatlands north of 37° latitude may be particularly vulnerable to climate change. [ABSTRACT FROM AUTHOR]

Peatlands are ecosystems that accumulate carbon (C) over long periods of time. The anoxic conditions created by prevailing water saturation, coupled with vegetation litter slow to decompose, reduces organic matter decay and allows net C accumulation. Open-water pools that cover many boreal and maritime peatlands are, however, net C sources to the atmosphere. Like lakes but contrary to the surrounding peat, pools are oxygenated environments and enhance the decomposition of organic matter. They are functionally different than peat but also than lakes, because of the organic nature of the matrix in which they are embedded. Using data from an undisturbed ombrotrophic bog of southern Canada, we show that pools are biogeochemical hotspots governed by internal processes and that they influence peatland structure. We also show that pools, while being net C sources to the atmosphere, may be key to sustaining the C accumulation function of peatlands by acting as hydrological buffers for the surrounding peat. [ABSTRACT FROM AUTHOR]

The inundation of boreal forests and peatlands through the construction of hydroelectric reservoirs can increase carbon dioxide (CO 2 ) and methane (CH 4 ) emission. To establish controls on emission rates, we incubated samples of forest and peat soils, spruce litter, forest litter and peatland litter collected from boreal ecosystems in northern Quebec for 16 weeks and measured CO 2 and CH 4 production rates under flooded or non-flooded conditions and varying oxygen concentration and temperature. CO 2 production under flooded conditions was less than under non-flooded conditions (5–71 vs. 5–85 mg C g − 1 C), but CH 4 production under flooded conditions was larger than under non-flooded conditions (1–8158 vs. 0–86 μg C g − 1 C). The average CO 2 and CH 4 production rate factor for flooded:non-flooded conditions was 0.76 and 1.32, respectively. Under flooded conditions, high oxygen concentrations increased CO 2 production in peat soils but decreased CH 4 production in forest and peat soils and spruce litter. Warmer temperatures (from 4 to 22 °C) raised both CO 2 production in peat soils and peatland litter, and CH 4 production in peat soils and spruce litter. This study shows that the direction and/or strength of CO 2 and CH 4 fluxes change once boreal forests and peatlands are inundated. [ABSTRACT FROM AUTHOR]

Climate change scenarios suggest that northern peatlands could become drier. To address the type and magnitude of vegetation change associated with persistent drying, we studied changes in biomass and leaf area index following drainage 85 years previously of a bog, using destructive sampling, allometric relationships, and optical measurements. Our results show a 10-fold increase in aboveground biomass between the reference site and the most severely drained site, resulting from the growth of a tree layer. The total leaf biomass increased slightly as a result of drainage, thus an increase in woody biomass was the main cause of the increase in aboveground biomass. Leaf area index approximately tripled in sites where trees grew. Sphagnum L. moss biomass decreased from 120 g·m−2 at the reference site (20% of all aboveground biomass) to 8 g·m−2 under the tree canopy (<1% of all aboveground biomass). The percentage of deciduous shrubs increased from 3% of the total shrub biomass in the reference site to 72% in the most severely drained site. Our results show that lowering the water table of a bog can have a profound effect on vegetation but the net effect of these changes on the role of the peatland as a carbon sink remains difficult to assess. [ABSTRACT FROM AUTHOR]

We compared the amount and composition of different aboveground biomass (BM) fractions of four mires with their net ecosystem CO2 exchange (NEE) measured by eddy covariance. We found clear differences in response of green biomass (GBM) of plant functional types (PFTs) to water table (WT), which resulted in larger spatial variation in GBM within a mire than variation between mires. GBM varied between mires from 126 ± 7 to 336 ± 16 g·m-2 (mean ± SE), while within mire variation at largest was from 157 ± 17 to 488 ± 20 g·m-2 (mean ± SE). GBM of dominant PFTs appeared to be better in explaining the peak growing season NEE than the total BM or GBM of a mire. The differences in photosynthetic capacity between PTFs had a major role, and thus a smaller GBM with different species composition could result in higher NEE than larger GBM. Vascular plant GBM, especially that of sedges, appeared to have a high impact on NEE. Eleven PFTs, defined here, appeared to capture well the internal variation within mires, and the differences in GBM between communities were explained by the water table response of PFTs. Our results suggest the use of photosynthesizing BM, separated into PFTs, in modelling ecosystem carbon exchange instead of using just total BM. [ABSTRACT FROM AUTHOR]

We examined aerobic and anaerobic microbial carbon dioxide (CO2) and methane (CH4) exchange in peat samples representing different profiles at natural, mined, mined-abandoned, and restored northern peatlands and characterized the nutrient and substrate chemistry and microbial biomass of these soils. Mining and abandonment led to reduced nutrient and substrate availability and occasionally drier conditions in surface peat resulting in a drastic reduction in CO2 and CH4 production, in agreement with previous studies. Owing mainly to wetter conditions, CH4 production and oxidation were faster in restored block-cut than natural sites, whereas in one restored site, increased substrate and nutrient availability led to much more rapid rates of CO2 production. Our work in restored block-cut sites compliments that in vacuum-harvested peatlands undergoing more recent active restoration attempts. The sites we examined covered a large range of soil C substrate quality, nutrient availability, microbial biomass, and microbial activities, allowing us to draw general conclusions about controls on microbial CO2 and CH4 dynamics using stepwise regression analysis among all sites and soil depths. Aerobic and anaerobic decomposition of peat was constrained by organic matter quality, particularly phosphorus (P) and carbon (C) chemistry, and closely linked to the size of the microbial biomass supported by these limiting resources. Methane production was more dominantly controlled by field moisture content (a proxy for anaerobism), even after 20 days of anaerobic laboratory incubation, and to a lesser extent by C substrate availability. As methanogens likely represented only a small proportion of the total microbial biomass, there were no links between total microbial biomass and CH4 production. Methane oxidation was controlled by the same factors influencing CH4 production, leading to the conclusion that CH4 oxidation is primarily controlled by substrate (that is, CH4) availability. Although restoring hydrology similar to natural sites may re-establish CH4 dynamics, there is geographic or site-specific variability in the ability to restore peat decomposition dynamics. [ABSTRACT FROM AUTHOR]

Northern peatlands contain up to 25% of the world's soil carbon (C) and have an estimated annual exchange of CO2-C with the atmosphere of 0.1–0.5 Pg yr−1 and of CH4-C of 10–25 Tg yr−1. Despite this overall importance to the global C cycle, there have been few, if any, complete multiyear annual C balances for these ecosystems. We report a 6-year balance computed from continuous net ecosystem CO2 exchange (NEE), regular instantaneous measurements of methane (CH4) emissions, and export of dissolved organic C (DOC) from a northern ombrotrophic bog. From these observations, we have constructed complete seasonal and annual C balances, examined their seasonal and interannual variability, and compared the mean 6-year contemporary C exchange with the apparent C accumulation for the last 3000 years obtained from C density and age-depth profiles from two peat cores. The 6-year mean NEE-C and CH4-C exchange, and net DOC loss are −40.2±40.5 (±1 SD), 3.7±0.5, and 14.9±3.1 g m−2 yr−1, giving a 6-year mean balance of −21.5±39.0 g m−2 yr−1 (where positive exchange is a loss of C from the ecosystem). NEE had the largest magnitude and variability of the components of the C balance, but DOC and CH4 had similar proportional variabilities and their inclusion is essential to resolve the C balance. There are large interseasonal and interannual ranges to the exchanges due to variations in climatic conditions. We estimate from the largest and smallest seasonal exchanges, quasi-maximum limits of the annual C balance between 50 and −105 g m−2 yr−1. The net C accumulation rate obtained from the two peatland cores for the interval 400–3000 bp (samples from the anoxic layer only) were 21.9±2.8 and 14.0±37.6 g m−2 yr−1, which are not significantly different from the 6-year mean contemporary exchange. [ABSTRACT FROM AUTHOR]

Peatlands cover a large area in Canada and globally (12% and 3% of the landmass, respectively). These ecosystems play an important role in climate regulation through the sequestration of carbon dioxide from, and the release of methane to, the atmosphere. Monitoring approaches, required to understand the response of peatlands to climate change at large spatial scales, are challenged by their unique vegetation characteristics, intrinsic hydrological complexity, and rapid changes over short periods of time (e.g., seasonality). In this study, we demonstrate the use of multitemporal, high spatial resolution (1 m2) hyperspectral airborne imagery (Compact Airborne Spectrographic Imager (CASI) and Shortwave Airborne Spectrographic Imager (SASI) sensors) for assessing maximum instantaneous gross photosynthesis (PGmax) in hummocks, and gravimetric water content (GWC) and carbon uptake efficiency in hollows, at the Mer Bleue ombrotrophic bog. We applied empirical models (i.e., in situ data and spectral indices) and we derived spatial and temporal trends for the aforementioned variables. Our findings revealed the distribution of hummocks (51.2%), hollows (12.7%), and tree cover (33.6%), which is the first high spatial resolution map of this nature at Mer Bleue. For hummocks, we found growing season PGmax values between 8 μmol m−2 s−1 and 12 μmol m−2 s−1 were predominant (86.3% of the total area). For hollows, our results revealed, for the first time, the spatial heterogeneity and seasonal trends for gravimetric water content and carbon uptake efficiency for the whole bog. [ABSTRACT FROM AUTHOR]