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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]

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]

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]

While considerable attention has been given to the measurement of mercury (Hg) and lead (Pb) concentrations and accumulation in detailed peat cores in central Canada, the geographic distribution and density of sampling are generally limited. Here, we use the Ontario Peatland Inventory to examine broad patterns of Hg and Pb concentration with depth, based on 338 peat cores (containing >1500 analyzed samples) from 127 bogs, fens and swamps located in southeastern, northeastern and northwestern sections of Ontario. Overall, Hg concentrations averaged 0.05 μg g −1 and that of Pb averaged 10.8 μg g −1 . Maximum values in the top 50 cm of the profiles are 0.08 μg g −1 and 26.2 μg g −1 for Hg and Pb, respectively. The ratio between these values (surface) and the values from below 100 cm (background), where peat likely accumulated before 1850 and industrial activities were limited, are 2.3 and 6.6 for Hg and Pb, respectively. The highest surface:background concentration ratios are generally found in the westernmost part of the province and in the southeast for Hg and around areas that are more heavily populated for Pb. Our results show that a vast amount of Hg and Pb are stored in Ontarian peatlands, although the spatial distribution of these stores varies. The rapid decomposition of peat in a changing climate could release these pollutants to the atmosphere. [ABSTRACT FROM AUTHOR]