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Aims: Peat is used as a major ingredient of growing media in horticulture. Peat extracted from bogs can be acidic and low in nutrient availability and is therefore mixed with liming agents, nutrients, surfactants, perlite and so on. This study aims to estimate the rates at which raw peat and the modified peat (‘growing media’) decompose to release carbon dioxide (CO2), to estimate the release of carbon (C) from liming agents and to estimate how peat biogeochemistry is changed.We obtained 28 and 24 samples of raw peat and 24 growing media from four peat extraction companies in Canada. Growing media were treated with horticultural additives. We incubated the samples under laboratory conditions, measuring CO2 production, tracer using δ13C\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\updelta }^{13}{\text{C}}$$\end{document}-CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document}, pH, C, nitrogen (N) content and humification indices (HIs) from infrared technology called Fourier transform-mid infrared (FT-MIR).C:N ratio, pH, dissolved organic carbon, bulk density and C content differed significantly (P < 0.05) between raw peats and growing media. There was more than a doubling of total CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} production from growing media compared to raw peat. HIs show higher values for the growing media, which could result from spectral band shifts in the growing media because of increased cation availability. δ13C\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\updelta }^{13}{\text{C}}$$\end{document}-CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} as a tracer showed an average 22% of the total CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} production orginated from added carbonate materials.Our results provide the rates (0.15 ± 0.017mgCO2-Cg−1d−1) at which horticultural peat decomposes and on the source of emitted CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document}. This will improve current estimates CO2 emissions from horticultural peat.Methods: Peat is used as a major ingredient of growing media in horticulture. Peat extracted from bogs can be acidic and low in nutrient availability and is therefore mixed with liming agents, nutrients, surfactants, perlite and so on. This study aims to estimate the rates at which raw peat and the modified peat (‘growing media’) decompose to release carbon dioxide (CO2), to estimate the release of carbon (C) from liming agents and to estimate how peat biogeochemistry is changed.We obtained 28 and 24 samples of raw peat and 24 growing media from four peat extraction companies in Canada. Growing media were treated with horticultural additives. We incubated the samples under laboratory conditions, measuring CO2 production, tracer using δ13C\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\updelta }^{13}{\text{C}}$$\end{document}-CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document}, pH, C, nitrogen (N) content and humification indices (HIs) from infrared technology called Fourier transform-mid infrared (FT-MIR).C:N ratio, pH, dissolved organic carbon, bulk density and C content differed significantly (P < 0.05) between raw peats and growing media. There was more than a doubling of total CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} production from growing media compared to raw peat. HIs show higher values for the growing media, which could result from spectral band shifts in the growing media because of increased cation availability. δ13C\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\updelta }^{13}{\text{C}}$$\end{document}-CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} as a tracer showed an average 22% of the total CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} production orginated from added carbonate materials.Our results provide the rates (0.15 ± 0.017mgCO2-Cg−1d−1) at which horticultural peat decomposes and on the source of emitted CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document}. This will improve current estimates CO2 emissions from horticultural peat.Results: Peat is used as a major ingredient of growing media in horticulture. Peat extracted from bogs can be acidic and low in nutrient availability and is therefore mixed with liming agents, nutrients, surfactants, perlite and so on. This study aims to estimate the rates at which raw peat and the modified peat (‘growing media’) decompose to release carbon dioxide (CO2), to estimate the release of carbon (C) from liming agents and to estimate how peat biogeochemistry is changed.We obtained 28 and 24 samples of raw peat and 24 growing media from four peat extraction companies in Canada. Growing media were treated with horticultural additives. We incubated the samples under laboratory conditions, measuring CO2 production, tracer using δ13C\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\updelta }^{13}{\text{C}}$$\end{document}-CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document}, pH, C, nitrogen (N) content and humification indices (HIs) from infrared technology called Fourier transform-mid infrared (FT-MIR).C:N ratio, pH, dissolved organic carbon, bulk density and C content differed significantly (P < 0.05) between raw peats and growing media. There was more than a doubling of total CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} production from growing media compared to raw peat. HIs show higher values for the growing media, which could result from spectral band shifts in the growing media because of increased cation availability. δ13C\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\updelta }^{13}{\text{C}}$$\end{document}-CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} as a tracer showed an average 22% of the total CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} production orginated from added carbonate materials.Our results provide the rates (0.15 ± 0.017mgCO2-Cg−1d−1) at which horticultural peat decomposes and on the source of emitted CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document}. This will improve current estimates CO2 emissions from horticultural peat.Conclusion: Peat is used as a major ingredient of growing media in horticulture. Peat extracted from bogs can be acidic and low in nutrient availability and is therefore mixed with liming agents, nutrients, surfactants, perlite and so on. This study aims to estimate the rates at which raw peat and the modified peat (‘growing media’) decompose to release carbon dioxide (CO2), to estimate the release of carbon (C) from liming agents and to estimate how peat biogeochemistry is changed.We obtained 28 and 24 samples of raw peat and 24 growing media from four peat extraction companies in Canada. Growing media were treated with horticultural additives. We incubated the samples under laboratory conditions, measuring CO2 production, tracer using δ13C\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\updelta }^{13}{\text{C}}$$\end{document}-CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document}, pH, C, nitrogen (N) content and humification indices (HIs) from infrared technology called Fourier transform-mid infrared (FT-MIR).C:N ratio, pH, dissolved organic carbon, bulk density and C content differed significantly (P < 0.05) between raw peats and growing media. There was more than a doubling of total CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} production from growing media compared to raw peat. HIs show higher values for the growing media, which could result from spectral band shifts in the growing media because of increased cation availability. δ13C\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\updelta }^{13}{\text{C}}$$\end{document}-CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} as a tracer showed an average 22% of the total CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document} production orginated from added carbonate materials.Our results provide the rates (0.15 ± 0.017mgCO2-Cg−1d−1) at which horticultural peat decomposes and on the source of emitted CO2\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${{\text{CO}}}_{2}$$\end{document}. This will improve current estimates CO2 emissions from horticultural peat. [ABSTRACT FROM AUTHOR]

The restoration and construction of wetlands offer opportunities to rewet soils, inhibit decomposition, and enhance nutrient retention in decomposing litters. Here, we report the decomposition rates and nutrient dynamics of macrophyte litters in intact, restored, and constructed wetlands. A 2.1‐year litterbag experiment of four common freshwater macrophytes (Phalaris arundinacea, Phragmites australis, Scirpus cyperinus, and Typha latifolia) was conducted in eight freshwater marshes (three intact, four restored, and one constructed) within three sites in Manitoba and Ontario, Canada, which varied in restoration age, inundation periods, and surrounding land uses. Litter mass loss and N and P dynamics were measured. Litter decomposition rates (k) followed the order of P. arundinacea (0.42 ± 0.03 year−1) > T. latifolia (0.31 ± 0.03 year−1) > P. australis (0.19 ± 0.01 year−1) > S. cyperinus (0.13 ± 0.01 year−1) in most wetlands and were positively correlated to the initial litter N concentration. Litters decomposed fastest under seasonally inundated conditions rather than permanent inundation. N and P retention in litters were significantly affected by both initial litter N and P concentration and wetland surrounding land uses. After 2.1 years of decomposition, the N:P ratio of all litters converged to 20 to 28:1, regardless of the initial litter N:P ratio or N or P concentrations. The effectiveness of wetland restoration in slowing decomposition and enhancing nutrient accumulation depends on the quality of the input litters and wetland characteristics, including inundated periods and surrounding anthropogenic disturbances. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the effect of drainage on peat properties, porewater chemistry, and peat decomposition proxies in an ombrogenous peatland in the Hudson Bay Lowland (HBL). We anticipated that drainage would change peatland hydrology, vegetation, and biogeochemistry, leading to an increase in peat decomposition. As indicators of peat biogeochemical change and potential proxies for peat decomposition, we compared peat porewater chemistry and in situ nutrient availability of different microforms in a pristine ombrogenous bog, with a bog that has been subject to gradual lowering of the water table by 20 to 80 cm for approximately 7 years prior to, and during, our study. We also examined the chemical composition of peat and peat leachates (organic matter) from Sphagnum and lichen-covered hummocks at each site. Nutrient availability was greater in pools at the drained bog, indicating mineralisation of the dry and bare peat surface. However, our results did not show evidence of significant peat biogeochemical change or advanced decomposition in hummocks at the drained bog, with no difference in nutrient availabilities, peat porewater chemistry, or peat leachate chemistry at the drained and pristine bog. We also found no significant difference in enzyme activity (phenol oxidases) in hummocks at each site, proposed to be an important factor for C loss from peatland ecosystems in drier conditions. Overall, the effects of drainage on peat properties, porewater chemistry, and peat chemical composition at our sites were small and varied for different vegetation-microform types. Although decomposition in drained peatlands is likely constrained by cool temperatures in the HBL, our results suggest that ecohydrological feedbacks at the microform scale may also be important in slowing decomposition in these peatlands. [ABSTRACT FROM AUTHOR]

We examined the concentration of nitrogen (N) and δ15N in vegetation and peat in the Mer Bleue bog, Ontario, Canada. Compared with other ecosystems, N concentration in bog plant foliage is low (generally < 1.2%), with more N stored belowground than in foliar tissues. The natural abundance of 15N varies by plant functional type, indicating different strategies for nutrient acquisition. δ15N values of evergreen shrubs and trees are lower (~− 5 to ~− 9‰) than sedges and herbs (~+ 1 to ~− 1‰), likely the result of ericoid mycorrhizal fungi, which retain 15N in fungal biomass, with preferential transfer of 14N to the host plant. Results suggest that N in Sphagnum moss capitula is derived from uptake of N from decomposing peat and litter, with δ15N values of − 8 to − 2‰, rather than from N2 fixation. Soil δ15N varies with depth, related to degree of decomposition and dominant plant species litter. Foliar N plays a critical role in influencing the rate of photosynthesis and CO2 exchange. Despite paucity of available inorganic N in the system, most bog plants (that is, evergreen shrubs) have adapted with conservative growth strategies. Owing to slow decomposition, N is stored in this system tightly bound with organic matter, with C:N ratios in deep peat ranging from 33:1 to 23:1 and small fluxes into, out of and within the system. An increase in N availability, through atmospheric N deposition or water table lowering, could jeopardize the C sink function of bogs by stimulating microbial decomposition of organic matter. In the long term, an increase in N cycling would shift plant community composition from Sphagnum and evergreen dominated to deciduous species, fundamentally altering bog ecosystem function. [ABSTRACT FROM AUTHOR]

Abstract Peat accumulation makes nutrient-limited ombrotrophic bogs important carbon sinks, while enhanced atmospheric nitrogen (N) deposition threatens this capacity. Here we show that the stoichiometry of peat and porewater, a control of plant growth and decomposition, has been altered in response to long-term N, phosphorus (P), and potassium (K) fertilization at Mer Bleue ombrotrophic bog in eastern Ontario, Canada. In N-fertilized peat, receiving up to an additional 6.4 g N m−2 y−1 above ambient deposition, we found N significantly (p < 0.05) greater, P both significantly greater and smaller dependent on treatment concentration, calcium (Ca) and K concentrations significantly lower, relative to control plots. In NPK-fertilized peat, P was greater than control while Ca was significantly smaller. In the porewater of N- and NPK-fertilized peat, we observed significantly more ammonium, nitrate, dissolved organic nitrogen, phosphate, and dissolved organic phosphorus than in the controls. Fourier-transform infrared (FTIR) spectroscopic analysis demonstrated that fertilization in all treatments increased decomposition, as indicated by residual enrichment of refractory moieties such as aromatics, carboxylates, and lignin, albeit only in the uppermost depths. Changes in peat quality may, however, not only relate to advanced decomposition but also to changes in litter input, as predominant vascular vegetation in the fertilized plots shared several features in FTIR spectra with samples of uppermost peat layers. Our results demonstrate that the peat in this ombrotrophic bog has responded to long-term fertilization with loss of Sphagnum moss and its filter function, increased shrub cover and enhanced decomposition. Highlights • Nutrient addition resulted in changes from moss to shrub dominance and a lowered peat surface. • There were significant increases in peat N and P and decreases in Ca and K concentrations. • Peat porewater had significant increases in N and P, with greatest changes in top 20 cm. • FTIR spectra of surface peat indicated advanced decomposition and altered vegetation. • These changes result from both direct nutrient additions and secondary vegetation changes. [ABSTRACT FROM AUTHOR]

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]

Background and aims: We examined changes in soil organic matter arising from conversion of a 45-year old pasture to a 10 yr. old native tree plantation in Panamá, to evaluate the effect of monoculture and mixtures.Methods: We intensively sampled the soil 0-10 cm depth in the pasture in 2001 and in 22 plantation plots in 2011, ranging from 5 monocultures to 3- and 6-species treatments; samples were also taken from an undisturbed forest site. Soil analyses included organic carbon (SOC) and δ13C.Results: Conversion of the pasture to tree plantation resulted in an overall loss of SOC of 0.6 kg m−2 (18%) in the top 10 cm, but neither tree species nor diversity had a significant effect. End-member δ13C values suggested that the contribution of C3 plants to SOC was increased from 26% in the pasture to 55% after 10 years of plantation and SOC turnover times were calculated to be 21-36 yr.Conclusions: The magnitude of the loss in soil SOC is smaller than the increases in tree biomass (~3 kg C m−2) and litter (~0.3 kg C m−2) in the plantation, but still a significant part of the ecosystem C balance. [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]

We assess the importance of publisher conduct and journal quality in determining the price and cost-effectiveness of journals in geography. Drawing on a database of 136 journals in which geographers publish, we examine the price of journals, publishers' market share, the determinants of journal prices, and the cost-effectiveness of journals. We find that commercial presses charge 2.3 times more for journals than society and university presses and 50 percent more for journals published on behalf of universities and societies. Journals in physical geography are almost twice as expensive as those in human geography and 43 percent of them can be considered “overpriced.” Four commercial presses hold 72 percent of the titles and 93 percent of the value of subscriptions, enabling them to exercise oligopolistic market power over pricing. Our multivariate analysis shows that the price of journals, of articles, and of citations in geography is driven by publisher conduct rather than journal quality as measured by citations accrued to articles. Geographers can further the transition underway in scientific publishing by self-archiving their published work, disseminating their findings through social networks, and paying closer attention to journal cost-effectiveness in choosing where to publish and review. [ABSTRACT FROM PUBLISHER]

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]

To examine where Canadian geographers publish their research, we used data on article publication compiled from the annual Directory of the Canadian Association of Geographers for 1981-82, 1991-92, 2001-02, and 2011-12. We find a very wide range of journals (1238) is used, but many of them are rarely used. Papers published from 1981 to 2012 increased 3.7-fold with a similar increase in the number of journals used. Commercial presses have come to dominate publishing, society presses and university presses are fewer today but open access journals have become more common. Only about one quarter of the journals used have a Thompson Reuter Impact Factor (IF) but the median IF of IF-rated journals used rose from 1.56 (1981-82) to 2.23 (2011-12). The Canadian Geographer is the most frequently used journal, but over time flagship geography journals have been replaced by interdisciplinary and thematic journals. Papers published per faculty rose from an average of 0.5 yr−1 in 1981-82 to 1.7 yr−1 in 2011-12, with a large variation in publication rates per faculty across departments, reflecting the research versus teaching focus. Canadian geographers are publishing well beyond the field, engaging with much larger audiences, and reaching top journals, to the benefit of the discipline. La publication des articles de revue en géographie canadienne Une analyse des revues dans lesquelles les géographes canadiens publient leurs travaux a été réalisée à partir des données sur la publication d'articles dans l'annuaire annuel de l'Association canadienne des géographes pour les années 1981-82, 1991-92, 2001-02 et 2011-12. On constate un éventail de revues très diversifié (1238) et que plusieurs d'entre elles sont utilisées rarement. De plus, entre 1981 et 2012, les articles parus ont augmenté de 3,7 fois et le nombre de revues qui en ont publié a crÛ du même ordre. Les maisons d'édition commerciales ont fini par dominer l'industrie. Si les maisons d'édition associatives et universitaires sont moins nombreuses aujourd'hui, il est plus courant de publier dans des revues en libre accès. Thompson Reuter calcule un facteur d'impact (FI) pour environ un quart de ces revues seulement, mais le FI médian des revues indexées ayant fait paraître un article est passé de 1,56 (1981-1982) à 2,23 (2011-12). Le Géographe canadien est la revue la plus sollicitée. Les revues phares spécialisées en géographie sont graduellement remplacées par des revues interdisciplinaires et thématiques. La moyenne d'articles que chaque professeur a fait paraître a augmenté de 0,5 par an en 1981-82 à 1,7 par an en 2011-12. D'un département à l'autre, les taux de publication par professeur varient en fonction de l'importance accordée à la recherche versus l'enseignement. Les géographes canadiens publient dans divers domaines autres que la géographie, permettant ainsi d'élargir le lectorat et d'accéder aux meilleures revues, ce qui valorise la discipline. [ABSTRACT FROM AUTHOR]

Previous studies have shown that atmospheric nitrogen (N) deposition is detrimental to sphagna, which are a group of mosses that are important for carbon cycling in northern peatlands. Little is known about species interactions, such as relative responses of tall moss Polytrichum strictum Menzies ex Brid. and sphagna. We studied the effects of N deposition on growth, abundance, and CO2 exchange of the moss species Sphagnum capillifolium (Ehrh.) Hedw. and Polytrichum strictum in an experiment at a temperate bog. Sphagnum growth and cover decreased significantly with high-dose N treatment (6.4 g N·m−2·year−1) in years 4 and 5 of treatment, whereas the same parameters increased for Polytrichum compared with the control. Net CO2 exchange, gross photosynthesis ( Pg), and dark respiration ( R) in the intact moss cores, which were measured in year 5 of treatment, were elevated in the cores that had been treated with the high-dose of N, compared with the control, and this was associated with increased abundance of Polytrichum. The moss cores where Polytrichum was removed, however, had increased mass-based R with the high-dose N treatment. Our results showed that S. capillifolium at Mer Bleue may be close to N saturation, as 5 years of high-dose N loading (6.4 g N·m−2·year−1 + background) was harmful to this species, possibly as a result of increased respiratory cost. Polytrichum strictum had a competitive advantage, at least in the short-term, through allocating excess N to growth. This change in moss layer composition deserves further attention, as a shift to more easily decomposable litter, without corresponding increases in plant production, could reduce the carbon sequestration of the bog. [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]

We measured changes in carbon (C), nitrogen (N) and phosphorus (P) concentrations and mass of 10 foliar litters decomposing over 12 years at 21 sites across Canada, ranging from subarctic to temperate, to evaluate the influence of litter quality (nature) and forest floor (nurture) on N and P dynamics. Most litters lost P faster than N, relative to C, except in one litter which had a high initial C:P quotient (2,122). Net N loss occurred at mass C:N quotients of between 33 and 68, positively correlated with the C:N quotient in the original litter, and net P loss likely occurred at C:P quotients between 800 and 1,200. Forest floor properties also influenced N and P dynamics: the higher the C:N or C:P quotient in the surface soil organic matter, the smaller the proportion of initial N or P left in the decomposing litter, relative to C. There was a convergence of C:N and C:P quotients as the litters decomposed, with an overall mass ratio of 427:17:1 when the litters reached 20% original C remaining. These results, covering a wide range of sites and litters and thus decomposition rates, showed that the C:N:P quotients followed similar trajectories and converged as the litters decomposed. The relative loss of N and P was affected by both the initial litter nutrient concentration and the chemistry of the site forest floor, with the former being more important than the latter, resulting in spatial variations in nutrient content of the forest floor. [ABSTRACT FROM AUTHOR]

Fine root production and its relationships to aboveground plant components and environmental drivers such as water table have been poorly quantified in peatland ecosystems, despite being the primary input of labile carbon to peat soils. We studied the relationship between fine root (< 1 mm) production, aboveground biomass and growing season water table within an ombrotrophic peatland in eastern Ontario. We installed 80 in-growth bags (10 cm diameter) to measure fine root production over the full range of 40 cm in water table depth. The point-intersect method was used to estimate peak aboveground biomass components (total, leaf and stem) for the 0.36 m area surrounding each in-growth bag. Mean fine root production was 108 ± 71 g m y and was strongly related to both aboveground biomass and water table. Linear regression analysis showed strong allometric relationships between fine root production and aboveground biomass for shrubs ( r = 0.61, p < 0.001), suggesting that fine root production estimates can be approximated using aboveground biomass data. Water table had a significant effect on the allocation of biomass to fine roots, leaves and stems with a deeper water table significantly increasing both fine root production at depth and at each depth increment. Shrub biomass allocation to leaves and stems similarly shifted, with greater investment in stems relative to leaves with a deeper water table. As a result, greater fine root biomass was produced per unit leaf biomass in areas with a deeper water table, illustrating an important tradeoff between leaf and fine root tissues in drier conditions. Our results indicate that any drop in water table will likely increase aboveground biomass stocks and the influx of labile carbon to peat soils via fine roots and leaves. [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]

We measured net ecosystem CO2 exchange (NEE), plant biomass and growth, species composition, peat microclimate, and litter decomposition in a fertilization experiment at Mer Bleue Bog, Ottawa, Ontario. The bog is located in the zone with the highest atmospheric nitrogen deposition for Canada, estimated at 0.8–1.2 g N m−2 yr−1 (wet deposition as NH4 and NO3). To establish the effect of nutrient addition on this ecosystem, we fertilized the bog with six treatments involving the application of 1.6–6 g N m−2 yr−1 (as NH4NO3), with and without P and K, in triplicate 3 m × 3 m plots. The initial 5–6 years have shown a loss of first Sphagnum, then Polytrichum mosses, and an increase in vascular plant biomass and leaf area index. Analyses of NEE, measured in situ with climate-controlled chambers, indicate that contrary to expectations, the treatments with the highest levels of nutrient addition showed lower rates of maximum NEE and gross photosynthesis, but little change in ecosystem respiration after 5 years. Although shrub biomass and leaf area increased in the high nutrient plots, loss of moss photosynthesis owing to nutrient toxicity, increased vascular plant shading and greater litter accumulation contributed to the lower levels of CO2 uptake. Our study highlights the importance of long-term experiments as we did not observe lower NEE until the fifth year of the experiment. However, this may be a transient response as the treatment plots continue to change. Higher levels of nutrients may cause changes in plant composition and productivity and decrease the ability of peatlands to sequester CO2 from the atmosphere. [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 showed that sandy subsoils beneath peat near Ramsey Lake, MI, contained 7.5 to 8.0 kg organic C (OC) m-2 to a depth of 70 cm, compared with 1.6 to 3.6 kg m-2 in adjacent forest soils, from which the peatland had evolved through paludification. Compared with the soils beneath the forest, those beneath the peat contained similar amounts of oxalate-extractable Al (Al0) and less Fe, owing to loss of Fe under reduced leached conditions beneath the peat. Most of the extractable Al in the mineral horizons beneath peat was organically bound. Atomic pyrophosphate-extractable (Fep + Alp) Fe + Al/C ratios were smaller (<0.2:1) in the mineral horizons beneath peat than in the forest mineral subsoils (generally >0.2:1), indicating larger inputs and retention in the mineral subsoils beneath peat. Concentration of OC in subsoil samples was strongly (r² = 0.58, p < 0.001) related to the subsoil Al, null-point dissolved organic C (DOC) and clay concentrations. A DOC sorption study using peat pore water ranging from 0 to 117 mg DOC L-1 revealed null-point DOC (DOCnp) concentrations (at which there is neither gain nor loss of OC by the soil) varied from <1 to 417 mg DOC L-1 and was primarily related to Feo (negatively), Alo (negatively), and C (positively). We suggest that the increase in mineral subsoil OC beneath peat is related to the sorption of DOC carried by pore water percolating through the mineral subsoil, combined with slow rates of mineralization of sorbed DOC under anoxic conditions. [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]

Summary 1Above-ground biomass was measured at bog hummock, bog hollow and poor-fen sites in Mer Bleue, a large, raised ombrotrophic bog near Ottawa, Ont., Canada. The average above-ground biomass was 587 g m-2 in the bog, composed mainly of shrubs and Sphagnum capitula. In the poor fen, the average biomass was 317 g m-2 , comprising mainly sedges and herbs and Sphagnum capitula. Vascular plant above-ground biomass was greater where the water table was lower, with a similar but weaker relationship for Sphagnum capitula and vascular leaf biomass. 2Below-ground biomass averaged 2400 g m-2 at the bog hummock site, of which 300 g m-2 was fine roots (< 2 mm diameter), compared with 1400 g m-2 in hollows (fine roots 450 g m-2 ) and 1200 g m-2 at the poor-fen site. 3Net Ecosystem Exchange (NEE) of CO2 was measured in chambers and used to derive ecosystem respiration and photosynthesis. Under high light flux (PAR of 1500 µmol m-2 s-1 ), NEE ranged across sites from 0.08 to 0.22 mg m-2 s-1 (a positive value indicates ecosystem uptake) in the spring and summer, but fell to –0.01 to –0.13 mg m-2 s-1 (i.e. a release of CO2 ) during a late-summer dry period. 4There was a general agreement between a combination of literature estimates of photosynthetic capacity for shrubs and mosses and measured biomass and summer-time CO2 uptake determined by the eddy covariance technique within a bog footprint (0.40 and 0.35–0.40 mg m-2 s-1 , respectively). 5Gross photosynthesis was estimated to be about 530 g m-2 year-1 , total respiration 460 g m-2 year-1 , and export of DOC, DIC and CH4 10 g m-2 year-1 , leaving an annual C sequestration rate of 60 g m-2 year-1 . Root... [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]

Ombrotrophic bogs can comprise a mosaic of vegetation patches and open-water pools, with hydrological and biogeochemical connections between pools and the surrounding peat and vegetation. To establish these connections, we studied the spatial heterogeneity of hydrology and water chemistry in two zones of distinct vegetation assemblages in the subboreal Grande plée Bleue peatland, southern Québec, Canada. We show that seasonal water-level fluctuations are greater and organic C, N and P concentrations are higher in the peat pore water of a forested zone than in a neighboring open-bog zone; that vegetation is responsible for 69% of the spatial variations in hydrology and water chemistry. Vegetation also explains 31% of the temporal variation in water chemistry, with higher increases in C, N and P concentrations over the growing season in the forested peat and pools than in the open-bog zone. We also show that C, N and P concentrations and water-level fluctuations in pools, especially during precipitation events, were lower than in the surrounding peat. Our results suggest the existence of small "watersheds" to the pools with water flowing in during wet and out during dry periods. Localized patterns emerge from the vegetation–hydrology–water chemistry interactions, with pools influencing the persistence of trees in the central part of an ombrotrophic bog. [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]

The article focuses on the concentration of dissolved organic carbon (DOC) in the streams and lakes of Great Britain. DOC is operationally defined as organic compounds in water that can pass through a .45 micrometer filter. DOC has a role in the metabolism of lake ecosystems and the protection of aquatic organisms. DOC-rich waters absorb ultraviolet radiation.

We examined concentrations of nitrogen (N) and phosphorus (P) and δ15N value in Sphagnum sections Acutifolia and Cuspidata inhabiting hummocks and hollows from eight bogs along a transect from ∼45 to ∼55°N in Ontario and Quebec. The N concentration in Sphagnum declined from south to north, correlating with a decrease in atmospheric N deposition. Although the overall N concentration was larger in hollows than hummocks, the pattern was inconsistent across the sites. There was a proportionally larger decline in P concentration from south to north and an overall larger P concentration in hollows than hummocks, but there were inconsistent differences across the sites. The N:P ratio ranged from 12:1 to 29:1, driven primarily by the variation in P concentration. Ratios of N and P concentration in Sphagnum capitulum:stem averaged 1.2:1, suggesting nutrient resorption from stem to capitulum during growth; the ratio rose with increasing N and P concentration in the capitulum. The δ15N value of Sphagnum rose from ∼−6‰ in the south to ∼−1‰ in the north, correlated with the decrease in Sphagnum N concentration and with a rise in the water table. We interpret this to indicate a greater dependence on N2-fixation for N acquisition in the northern and wetter sites. [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]

The Great Recession of 2007–2009 had profound effects on all sectors of the U.S. economy. In this article we assess the relationship between the academic job market in U.S. geography and the business cycle. Specifically, we examine the responsiveness of the job market to the business cycle since the early 1970s, the impacts of the Great Recession on hiring, and how hiring networks changed with the recession. For our analyses we draw on data from American Association of Geographers (AAG) publications, principally the AAG Newsletter (Jobs in Geography) and the Guide to Geography Programs in the Americas. We find that (1) the academic job market in geography is tightly linked to the business cycle and highly vulnerable to recessions, (2) the 2007–2009 recession destabilized demand and supply in the market with impacts on hiring lasting at least ten years, and (3) hiring networks among PhD-granting programs contracted, had lower connectivity, and witnessed a reshuffling of the top-hiring schools postrecession. Overall, the Great Recession dampened the likelihood of securing a tenure-track position in U.S. geography more so than any recession over the past fifty years. The arrival of COVID-19 and the accompanying contraction of gross domestic product are likely to further adversely affect faculty hiring. Key Words: economic recession, employment, higher education, university jobs. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the relationships between CO2 and CH4 fluxes across space and time at a temperate ombrotrophic bog in Canada to assess the coupling between plant production and CH4 emissions. Based on periodic manual chamber measurements, we show that maximum net ecosystem CO2 exchange (NEEmax) was a good predictor of the spatial variations in CH4 flux among the wetter Eriophorum and lawn sites (r 2 = 0.61–0.88), but not the drier hummock sites (r 2 = 0.04–0.49). Also, we observed large interannual variability in the NEEmax-CH4 relationship at the Eriophorum and lawn sites, with a smaller regression slope in 2010 that had a seasonal mean water table 8 cm lower than in 2009. Results of cross-correlation of instantaneous gross ecosystem production (GEP) and CH4 flux from autochambers show a moderate relationship (σ = −0.31) in the Eriophorum community at a lag of 9–12 h, suggesting a rapid turnover of recent photosynthate for methanogenesis. On the other hand, we found in two Maianthemum-dominated chambers that the temperature-independent residuals of daily mean CH4 flux lagged behind GEP by 18–26 days at the seasonal scale. The lagged correlations between GEP and CH4 flux by month were particularly strong in the late growing season in the Eriophorum and Maianthemum/Ledum communities. Our results suggest the presence of spatial and temporal coupling of plant production and CH4 emissions in this bog, whose strength varies with species composition, water table position, and plant phenology. [Copyright &y& Elsevier]

Abstract: To establish whether methane (CH4) biogeochemistry could be useful in detecting graves, we measured soil–atmosphere CH4 fluxes, pore air CH4 concentrations, atmospheric CH4 concentrations near the soil surface, and soil aerobic CH4 consumption and anaerobic CH4 production potentials at a graveyard in southern Quebec, Canada, which contained cadavers of zoo animals buried at least a decade before. Soil CH4 fluxes ranged from small rates of consumption in well-drained, non-grave sites (0 to −2mgm−2 d−1) to >30mgm−2 d−1 in suspected graves and wetter sites and >1500mgm−2 d−1 at open gravesites. Pore air CH4 concentrations were sub-ambient in well-drained, non-grave soils, confirming net consumption, whereas concentrations were above ambient around graves. Sampling of air for CH4 concentration just above the soil surface after stable meteorological conditions revealed spatial patterns that were related to the occurrence of graves. There were large variations in the soil aerobic CH4 consumption and anaerobic CH4 production potentials in laboratory incubations, providing evidence of the changes in methanotrophic and methanogenic communities and substrate characteristics promoting increased rates of CH4 consumption and/or production associated with cadaver burial. These results suggest that CH4 biogeochemistry can be useful in detecting graves, though its utility will be heavily dependent on the mass, depth, age and nature of the burials as well as the local environment, such as temperature and especially soil drainage, to separate the effect of cadavers from that of the water table. [Copyright &y& Elsevier]

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]

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]

This study uses life-cycle analysis to examine the net greenhouse gas (GHG) emissions from the Canadian peat industry for the period 1990-2000. GHG exchange is estimated for land-use change, peat extraction and processing, transport to market, and the in situ decomposition of extracted peat. The estimates, based on an additive GHG accounting model, show that the peat extraction life cycle emitted 0.54 × 106 t of GHG in 1990, increasing to 0.89 × 106 t in 2000 (expressed as CO2 equivalents using a 100-y time horizon). Peat decomposition associated with end use was the largest source of GHGs, comprising 71 % of total emissions during this 11-y period. Land use change resulted in a switch of the peatlands from a OHO sink to a source and contributed an additional 15%. Peat transportation was responsible for 10% of total OHO emissions, and extraction and processing contributed 4%. It would take approximately 2000 y to restore the carbon pool to its original size if peatland restoration is successful and the cutover peatland once again becomes a net carbon sink. [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]

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]

Wetlands are the largest natural source of atmospheric methane. Here, we assess controls on methane flux using a database of approximately 19 000 instantaneous measurements from 71 wetland sites located across subtropical, temperate, and northern high latitude regions. Our analyses confirm general controls on wetland methane emissions from soil temperature, water table, and vegetation, but also show that these relationships are modified depending on wetland type (bog, fen, or swamp), region (subarctic to temperate), and disturbance. Fen methane flux was more sensitive to vegetation and less sensitive to temperature than bog or swamp fluxes. The optimal water table for methane flux was consistently below the peat surface in bogs, close to the peat surface in poor fens, and above the peat surface in rich fens. However, the largest flux in bogs occurred when dry 30-day averaged antecedent conditions were followed by wet conditions, while in fens and swamps, the largest flux occurred when both 30-day averaged antecedent and current conditions were wet. Drained wetlands exhibited distinct characteristics, e.g. the absence of large flux following wet and warm conditions, suggesting that the same functional relationships between methane flux and environmental conditions cannot be used across pristine and disturbed wetlands. Together, our results suggest that water table and temperature are dominant controls on methane flux in pristine bogs and swamps, while other processes, such as vascular transport in pristine fens, have the potential to partially override the effect of these controls in other wetland types. Because wetland types vary in methane emissions and have distinct controls, these ecosystems need to be considered separately to yield reliable estimates of global wetland methane release. [ABSTRACT FROM AUTHOR]

Recently, methanotrophic members of the phylum V errucomicrobia have been described, but little is known about their distribution in nature. We surveyed methanotrophic bacteria in geothermal springs and acidic wetlands via pyrosequencing of 16 S rRNA gene amplicons. Putative methanotrophic V errucomicrobia were found in samples covering a broad temperature range (22.5-81.6° C), but only in acidic conditions ( pH 1.8-5.0) and only in geothermal environments, not in acidic bogs or fens. Phylogenetically, three 16 S rRNA gene sequence clusters of putative methanotrophic V errucomicrobia were observed. Those detected in high-temperature geothermal samples (44.1-81.6° C) grouped with known thermoacidiphilic ' M ethylacidiphilum' isolates. A second group dominated in moderate-temperature geothermal samples (22.5-40.1° C) and a representative mesophilic methanotroph from this group was isolated (strain LP2 A). Genome sequencing verified that strain LP2 A possessed particulate methane monooxygenase, but its 16 S rRNA gene sequence identity to ' M ethylacidiphilum infernorum' strain V4 was only 90.6%. A third group clustered distantly with known methanotrophic V errucomicrobia. Using pmoA-gene targeted quantitative polymerase chain reaction, two geothermal soil profiles showed a dominance of LP2 A-like pmoA sequences in the cooler surface layers and ' M ethylacidiphilum'-like pmoA sequences in deeper, hotter layers. Based on these results, there appears to be a thermophilic group and a mesophilic group of methanotrophic V errucomicrobia. However, both were detected only in acidic geothermal environments. [ABSTRACT FROM AUTHOR]

To study vegetation feedbacks of nutrient addition on carbon sequestration capacity, we investigated vegetation and ecosystem CO2 exchange at Mer Bleue Bog, Canada in plots that had been fertilized with nitrogen (N) or with N plus phosphorus (P) and potassium (K) for 7-12 years. Gross photosynthesis, ecosystem respiration, and net CO2 exchange were measured weekly during May-September 2011 using climate-controlled chambers. A substrate-induced respiration technique was used to determine the functional ability of the microbial community. The highest N and NPK additions were associated with 40% less net CO2 uptake than the control. In the NPK additions, a diminished C sink potential was due to a 20-30% increase in ecosystem respiration, while gross photosynthesis rates did not change as greater vascular plant biomass compensated for the decrease in Sphagnum mosses. In the highest N-only treatment, small reductions in gross photosynthesis and no change in ecosystem respiration led to the reduced C sink. Substrate-induced microbial respiration was significantly higher in all levels of NPK additions compared with control. The temperature sensitivity of respiration in the plots was lower with increasing cumulative N load, suggesting more labile sources of respired CO2. The weaker C sink potential could be explained by changes in nutrient availability, higher woody : foliar ratio, moss loss, and enhanced decomposition. Stronger responses to NPK fertilization than to N-only fertilization for both shrub biomass production and decomposition suggest that the bog ecosystem is N-P/K colimited rather than N-limited. Negative effects of further N-only deposition were indicated by delayed spring CO2 uptake. In contrast to forests, increased wood formation and surface litter accumulation in bogs seem to reduce the C sink potential owing to the loss of peat-forming Sphagnum. [ABSTRACT FROM AUTHOR]

The use of Remotely Piloted Aircraft Systems (RPAS) as well as newer automated unmanned aerial vehicles is becoming a standard method in remote sensing studies requiring high spatial resolution (<1 m) and very precise temporal data to capture phenological events. In this study we use a low cost rotorcraft to map Eriophorum vaginatum at Mer Bleue, an ombrotrophic bog located east of Ottawa, ON, Canada. We focus on E. vaginatum because this sedge plays an important role in methane (CH4) gas exchange in peatlands. Using the remote controlled rotorcraft we were able to record, process, and mosaic 11.1 hectares of 4.5 cm spatial resolution imagery extracted from individual frames of video recordings (post georegistration RMSE 4.90 ± 4.95 cm). Our results, based on a supervised classification (96% accuracy) of the red, green, blue image planes, indicate a total tussock cover of 2,417 m2. Because the basal area of the plant is more relevant for calculating its contribution to the CH4 flux, the tussock area was related to the basal area from field data (R2 = 0.88, p < 0.0001). Our final results indicate a total basal area of 1,786 ± 62.8 m2. Based on temporal measurements of CH4 flux from the peatland as a whole that vary over the growing season, we estimate the E. vaginatum contribution to range from 3.0% to 17.3% of that total. Overall, our low cost approach was an effective non-destructive way to derive E. vaginatum coverage and estimate CH4 exchange over the growing season. [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 investigated soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) exchanges in an age-sequence (4, 17, 32, 67 years old) of eastern white pine ( Pinus strobus L.) forests in southern Ontario, Canada, for the period of mid-April to mid-December in 2006 and 2007. For both CH4 and N2O, we observed uptake and emission ranging from −160 to 245 μg CH4 m−2 h−1 and −52 to 21 μg N2O m−2 h−1, respectively (negative values indicate uptake). Mean fluxes from mid-April to mid-December across the 4, 17, 32, 67 years old stands were similar for CO2 fluxes (259, 246, 220, and 250 mg CO2 m−2 h−1, respectively), without pattern for N2O fluxes (−3.7, 1.5, −2.2, and −7.6 μg N2O m−2 h−1, respectively), whereas the uptake rates of CH4 increased with stand age (6.4, −7.9, −10.8, and −23.3 μg CH4 m−2 h−1, respectively). For the same period, the combined contribution of CH4 and N2O exchanges to the global warming potential (GWP) calculated from net ecosystem exchange of CO2 and aggregated soil exchanges of CH4 and N2O was on average 4%, <1%, <1%, and 2% for the 4, 17, 32, 67 years old stand, respectively. Soil CO2 fluxes correlated positively with soil temperature but had no relationship with soil moisture. We found no control of soil temperature or soil moisture on CH4 and N2O fluxes, but CH4 emission was observed following summer rainfall events. LFH layer removal reduced CO2 emissions by 43%, increased CH4 uptake during dry and warm soil conditions by more than twofold, but did not affect N2O flux. We suggest that significant alternating sink and source potentials for both CH4 and N2O may occur in N- and soil water-limited forest ecosystems, which constitute a large portion of forest cover in temperate areas. [ABSTRACT FROM AUTHOR]

This paper presents soil fluxes of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) from 12 sites located in four major forest types, black spruce (Picea mariana (Mill.) BSP), jack pine (Pinus banksiana Lamb.), aspen (Populus spp.), and alder (Alnus spp.) stands, in the Eastmain and Chibougamau regions of Quebec. Fluxes were determined with closed chambers during the snow-free period from May to October 2007. Well-drained black spruce, jack pine, and aspen forest soils were net sinks of atmospheric CH4 (–0.33 ± 0.11 mg·m–2·day–1), while alder-dominated wetland soils were sources of CH4 (0.45 ± 0.12 mg·m–2·day–1). The cut-over alder wetland soil produced 131 times more CH4 than the undisturbed wetland soil. Soil moisture and temperature mainly regulated CH4 fluxes. N2O fluxes from these forest soils were highly variable and smaller (1.6 ± 0.33 µg N·m–2·h–1) than those from deciduous forest soils. N2O emission from the cut-over black spruce forest soil was 2.7 times greater than that from the mature black spruce forest soil. Large C/N ratios (27 to 78) and slow soil N mineralization and nitrification rates in these forest soils may have led to small N2O fluxes. CO2 emissions from these forest soils, ranging from 0.20 to 2.7 g·m–2·day–1, were mainly controlled by soil temperature. [ABSTRACT FROM AUTHOR]

Abstract: We conducted laboratory incubation experiments to elucidate the influence of forest type and topographic position on emission and/or consumption potentials of nitrous oxide (N2O) and methane (CH4) from soils of three forest types in Eastern Canada. Soil samples collected from deciduous, black spruce and white pine forests were incubated under a control, an NH4NO3 amendment and an elevated headspace CH4 concentration at 70% water-filled pore space (WFPS), except the poorly drained wetland soils which were incubated at 100% WFPS. Deciduous and boreal forest soils exhibited greater potential of N2O and CH4 fluxes than did white pine forest soils. Mineral N addition resulted in significant increases in N2O emissions from wetland forest soils compared to the unamended soils, whereas well-drained soils exhibited no significant increase in N2O emissions in-response to mineral N additions. Soils in deciduous, boreal and white pine forests consumed CH4 when incubated under an elevated headspace CH4 concentration, except the poorly drained soils in the deciduous forest, which emitted CH4. CH4 consumption rates in deciduous and boreal forest soils were twice the amount consumed by the white pine forest soils. The results suggest that an episodic increase in reactive N input in these forests is not likely to increase N2O emissions, except from the poorly drained wetland soils; however, long-term in situ N fertilization studies are required to validate the observed results. Moreover, wetland soils in the deciduous forest are net sources of CH4 unlike the well-drained soils, which are net sinks of atmospheric CH4. Because wetland soils can produce a substantial amount of CH4 and N2O, the contribution of these wetlands to the total trace gas fluxes need to be accounted for when modeling fluxes from forest soils in Eastern Canada. [Copyright &y& Elsevier]