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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]

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]

Abstract: In large regions of Europe and North America, peatlands have been exposed to elevated rates of atmospheric nitrogen (N) deposition. We investigated the fate of experimentally added N (NH4 15NO3) at two different N loads (1.2 and 4.7 g N m−2 yr−1) and water tables (1 and 32 cm) in intact cores from two peatlands, located in Central and Eastern Canada. The sites receive an estimated total N load of 0.6 g m−2 a−1 and 1.5 g m−2 yr−1, excluding nitrogen fixation. In all treatments, experimentally added nitrate (NO3 −) was fully (96–99%) and ammonium (NH4 +) mostly (81–97%) retained by the plant cover, mainly consisting of Sphagnum mosses, or in the unsaturated zone below. However, on average only 48% of the 15N were recovered from the plant cover, and substantial amounts were found in depth layers of 2–6 cm (21–46%) and 8–12 cm (1.4–10.8%) below the moss surface. The amount of 15N retained also significantly decreased with a lower water table from 56± 9% to 40±10%. These findings document a substantial mobility of N, particularly during water table drawdown. Analysis of 15N by a sequential diffusion procedure revealed a transfer of 15N from NO3 − into NH4 + and dissolved organic N (DON), but the contents of 15N in these pools accounted for less than 1% of the total N, natural background subtracted. The mass flux of dissolved 15N into the peat was small compared to the total mass flux of 15N. The accumulation of 15N in the bulk peat must have been caused by a mechanism that was not investigated, possibly by transport of particulate organic N. [Copyright &y& Elsevier]

The effects of peat bog harvesting and restoration on dissolved organic matter (DOM) are poorly known although DOM represents the most mobile part of organic matter in peat. The aims of our study were: (i) to determine concentrations and properties of DOM in a series of natural, harvested, and restored peatlands in eastern Que´bec and (ii) to relate DOM to CO2 efflux from these bogs. We sampled pore waters at eight peat bogs and determined dissolved organic carbon (DOC) concentrations, humification indices derived from synchronous fluorescence spectra (humification index (HIX), ratio of intensities at 470 and 400 nm), specific absorption at 280 nm, and the humic acid (HA) content. DOC concentrations ranged from 35 to 625 mg C l−1. The highest values were observed at a block-cut (BC) site where the ditches had been closed to stimulate restoration. This resulted in limited external drainage, DOM accumulation in deeper horizons, and an enrichment of the poorly biodegradable humic acids to about 60% of the bulk DOM. DOC concentrations increased immediately during harvesting up to 188 mg C l−1 as a result of this ecosystem disturbance. Afterwards, DOC concentrations decreased which might be due to a low content of potential DOM of the remaining little oxidised peat. The enhanced decomposition of the remaining peat during the restoration process seems to be important for a new build-up of potential DOM, which is indicated by reincreasing DOC concentration during the restoration process. We could not relate spectroscopic properties of DOM to peat harvesting and restoration. The portion of humic acids was inversely related to CO2 efflux, indicating low substrate quality of humic acids in pore waters. The seasonal average humification indices of DOM where humic acids had been removed were positively correlated with the seasonal CO2 efflux from the eight sites, indicating that high respiration results in an enrichment of more aromatic and complex DOM molecules. The relationships suggest that DOM composition affects CO2 efflux from peat bogs and is also driven by respiration and CO2 efflux. [Copyright &y& Elsevier]