Bogs and fens cover 6% and 21%, respectively, of the 140,329 km2 Oil Sands Administrative Area in northern Alberta. Development of the oil sands has led to increasing atmospheric N deposition, with values as high as 17 kg N·ha−1·yr−1; regional background deposition is <2 kg N·ha−1·yr−1. Bogs, being ombrotrophic, may be especially susceptible to increasing N deposition. To examine responses to N deposition, over five years, we experimentally applied N (as NH4NO3) to a bog near Mariana Lake, Alberta, unaffected by oil sands activities, at rates of 0, 5, 10, 15, 20, and 25 kg N·ha−1·yr−1, plus controls (no water or N addition). Increasing N addition: (1) stimulated N2 fixation at deposition <3.1 kg N·ha−1·yr−1, and progressively inhibited N2 fixation as N deposition increased above this level; (2) had no effect on Sphagnum fuscum net primary production (NPP) in years 1, 2, and 4, but inhibited S. fuscum NPP in years 3 and 5; (3) stimulated dominant shrub and Picea mariana NPP; (4) led to increased root biomass and production; (5) changed Sphagnum species relative abundance (decrease in S. fuscum, increase in S. magellanicum, no effect on S. angustifolium); (6) led to increasing abundance of Rhododendron groenlandicum and Andromeda polifolia, and to vascular plants in general; (7) led to increasing shrub leaf N concentrations in Andromeda polifolia, Chamaedaphne calyculata, Vaccinium oxycoccos, V. vitis‐idaea, and Picea mariana; (8) stimulated cellulose decomposition, with no effect on S. fuscum peat or mixed vascular plant litter decomposition; (9) had no effect on net N mineralization rates or on porewater NH4+‐N, NO3−‐N, or DON concentrations; and (10) had minimal effects on peat microbial community composition. Increasing experimental N addition led to a switch from new N being taken up primarily by Sphagnum to being taken up primarily by shrubs. As shrub growth and cover increase, Sphagnum abundance and NPP decrease. Because inhibition of N2 fixation by increasing N deposition plays a key role in bog structural and functional responses, we recommend a N deposition critical load of 3 kg N·ha−1·yr−1 for northern Alberta bogs.

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2016 (April): Linkages between spatiotemporal patterns of environmental factors and distribution of plant assemblages across a boreal peatland complex.Here we examine the arrangement of plant species across an oligotrophic bog/poor fen peatland complex in the North American boreal plain and the relationships of these species to their physical and chemical environment. A semi-uniform spatial sampling approach was utilized to describe the species assemblages, pore-water chemistry and physical condition of 100 plots throughout a single peatland complex. Regardless of sharing the same ground cover of Sphagnum mosses, the remaining species separated into four distinct assemblages, each with unique indicators. These species groups along with associated chemical and physical factors are organized into four ecosites: bog, margin (edge) and two poor fen ecosites. The plant assemblages of this peatland have a complex relationship with numerous gradients, both physical and chemical, including depth to water table, shade, pH, nutrient and base cation. Rather than being homogenous across the landscape, most environmental variables exhibit distinct spatial patterns and do so in relationship to the plant assemblages, forming spatially distinct ecosites across the complex. Base cation concentrations play a smaller role than previously thought in differentiating these ecosites, and in addition to shade and depth to water table, nitrogen in the form of dissolved organic nitrogen was highly related to the placement of these ecosites. Many significant chemical factors appear related to evaporative water loss within the peatland complex, and these chemical factors are used to differentiate the ecosites. However, the mediation of evaporative water loss is due largely to self-generated responses of the plant assemblages related to shade through plant morphology and peat acrotelm development related to depth to water table. We conclude that plant species and associated environmental gradients act together to form spatially distinct ecosites. The distribution of these ecosites within this large, environmentally complex peatland is largely controlled by differing self-generated responses along the hydrotopographical gradient of differential water loss.

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