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

The large accumulation of 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]

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]

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

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