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Peatland Vascular Plant Leaf N Concentrations (10 Species) From Leaves Collected From N-Addition Plots in an Alberta Peatland, 2011-2015

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 levels <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 Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). In July of each year, we collected new growth of ten species of vascular plants, returned them to the lab, cleaned them, dried and ground them, and ran them on a Flash EA 1112 Series CN Soil Analyzer. Leaf N concentration responses to increasing N input differed between species. Increasing N input led to increasing leaf N concentrations in A. polifolia, C. calyculata, V. vitis-idaea, and V. oxycoccos, with differences in N concentrations between years for all of these species except V. vitis-idaea. There was no leaf N concentration response to increasing N input for E. vaginatum, R. chamaemorus, S. trifolia, or K. polifolia. Water input alone had no significant effect on leaf N concentration for any of the species (p >= 0.18). Although aboveground growth of bog vascular plants may be a general response to increasing N deposition, we do not have a species-specific mechanistic understanding of how growth and leaf/needle N concentrations respond to increasing N deposition, however, there appeared to be no strong evidence for luxury consumption of N.

Sphagnum fuscum Capitulum Density, Mass, and N Concentrations From N-Addition Plots in an Alberta Peatland, 2013-2015

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 levels <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 Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). From 2013-2015, we examined the effects of N addition on changes in S. fuscum capitulum mass density, N concentrations, and N contents in plants collected in early July (summer) and early October (fall). In each year, capitulum mass density decreased with increasing N input at equal rates in summer-collected and fall-collected plants, although CMD was consistently higher in fall-collected than in summer-collected plants. For both summer- and fall-collected plants, capitulum N concentrations were unaffected by N inputs, although N concentrations were consistently higher in summer (14.4 ± 0.3 mg g-1) than in fall (0.7 ± 0.1 mg g-1). Combining CMD and capitulum N concentrations, capitulum N contents overall averaged 1.16 ± 0.04 g m-2. Capitulum N contents decreased with increasing N input, with the response being stronger in 2013 than in 2014/2015 . These results, combined with stem and capitulum responses at Mariana Lakes Bog, suggest that increasing N loading affects not only S. fuscum NPP, but also the way in which S. fuscum grows.

Net N Mineralization Rates in Peat From N-Addition Plots in an Alberta Peatland, 2011-2014

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 levels <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 Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). From 2011 through 2014, we quantified net N mineralization in each plot using the in situ buried polyethylene bag technique. Concentrations of initial KCl-extractable NH4 +-N, NO3 --N, and DIN in the top 10 cm of peat were unaffected by N inputs. We hypothesized that as N deposition increases to a level that exceeds the capacity of the bog vegetation to take up N, net N mineralization in surface peat would be inhibited by higher NH4 +-N availability, net nitrification would be stimulated by higher NH4 +-N availability (cf. McGill and Cole 1981, Robertson and Groffman 2015), and concentrations of DIN in porewater at the top of the water table would increase, as DIN bypasses interception by the ground layer vegetation. None of these hypotheses was supported. Experimentally added NH4 +-N and NO3 --N apparently appear to be rapidly immobilized. This immobilization prevents experimentally added DIN from moving downward through the peat to the bog water table.

Nitrogen Fixation Responses in Sphagnum fuscum to N-Additions to an Alberta Peatland, 2012-2015

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 levels <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 Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). We measured N2-fixation using the acetylene reduction technique between 2012 and 2015. All measurements were made between June and August. Mean acetylene reduction rates ranged from 2.2 mg m-2 da-1 (late June 2012) to 12.3 mg m-2 da-1 (late July 2014). Averaged across all measurement dates, rates were highest in the 5 kg N ha-1 yr-1 treatment, and decreased with increasing N loading. The acetylene reduction/N2 fixation response to N addition was described by a segmented linear regression, with rates increasing as N addition increased to 3.1 ± 1.5 kg N ha-1 yr-1 and decreasing with further increases in N addition. Water addition alone had no significant effect on N fixation rates on any of the measurement dates (p >= 0.79). While increasing N deposition may not substantively change total inputs of new N to bogs, the form on new N inputs shifts to inorganic N in deposition, rather than organic N produced by the microorganisms that are fixing N2.

Nitrogen Deposition to an Alberta Bog as Measured with Mixed-bed Ion Exchange Resin Tube Collectors, 2011-2015

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 levels <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 Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). Resin tubes filled with mixed-bed ion exchange resin were swapped in and out at each collection/deployment date (mid-May and mid-October of each year). Upon collection, resins were extracted with 1M KI and analyzed for inorganic N concentrations. Deposition of NH4 +-N, NO3 --N, and DIN averaged 187 ± 11, 237 ± 13, and 426 ± 19 μg m-2 da-1, corresponding to 0.68 ± 0.04, 0.87 ± 0.05, and 1.55 ± 0.07 kg N ha-1 yr-1, with no significant differences between open and throughfall collectors for any of the three measured parameters (p >= 0.63). Deposition of NH4 +-N was significantly higher during the growing season (averaging 240 μg m-2 da-1) than during the winter months (averaging 121 μg m-2 da-1) (p = 0.0004), while NO3 --N and DIN deposition did not differ significantly between winter and summer (p = 0.06 and 0.13, respectively).

Vascular Root Biomass and N Concentrations at Two Depths in an Alberta Peatland Subjected to Increasing Nitrogen Deposition, 2014-2015

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 levels <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 Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). From 2014-2015, we examined the effects of N addition on root production and nitrogen assimilation in those roots by measuring root biomass at two depths and root production over one and two years. Root biomass in the 0-15 cm and 15-30 cm depth increments in peat increased with increasing N input; the response was similar in the two depth increments. Root production integrated over the top 30 cm of peat increased with increasing N input at a rate of 5.3 g m-2 yr-1 with an increase in N input of 1 kg N ha-1 yr-1. Water addition alone had no significant effect on root biomass (p > 0.72) or root production. Given the rather consistent finding increasing N deposition stimulates aboveground vascular plant biomass and production, and our results that root biomass and production at Mariana Lakes Bog are stimulated as well, further work on belowground responses seems warranted.

Shrub Growth, NPP, and Nitrogen Assimilation for Two Years in an Alberta Peatland Subjected to Increasing Nitrogen Deposition, 2014-2015

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 levels <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 Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). In July of each year, we collected new growth of the three shrub species, returned them to the lab, and analyzed them. Non-destructive measurement of aboveground NPP for the three dominant shrub species, Andromeda polifolia, Chamaedaphne calyculata, and Rhododendron groenlandicum was based on allometric equations developed. Results for species were varied, however, water addition alone had no significant effect on NPP for any of the species or for the dominant shrubs combined in either 2014 or 2015 (p >= 0.47). The mass of newly produced shoot segments for Chamaedaphne calyculata, Andromeda polifolia, Rhododendron groenlandicum, and these three dominant shrubs combined all increased with increasing N input. As N input increased, the number of newly produced shoots (vegetative buds m-2) increased linearly for A. polifolia and the three shrub species combined. The number of newly produced shoots increased up to 16.6 ± 2.5 kg N ha-1 yr-1 and then decreased for C. calyculata and was unaffected for R. groenlandicum. Shrub growth response to increased N could lead to a shading out of the underlayer of mosses changing the bog and potentially compromising its structure and function.

Sphagnum fuscum Growth and N Concentration in an Alberta Peatland Subjected to Increasing Nitrogen Deposition, 2011-2015

Pore Water Concentrations of Nitrogen From N-Addition Plots in an Alberta Peatland, 2011-2015

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 levels <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 Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). We collected surface pore water from all plots several times a year throughout the 5 year experiment. Porewater NH4 +-N, NO3 --N, and DON concentrations were unaffected by N input in any of the five years (rmANOVA; p = 0.44, 0.37, and 0.82, respectively). We hypothesized that as N deposition increases to a level that exceeds the capacity of the bog vegetation to take up N, net N mineralization in surface peat would be inhibited by higher NH4 +-N availability, net nitrification would be stimulated by higher NH4 +-N availability, and concentrations of DIN in porewater at the top of the water table would increase, as DIN bypasses interception by the ground layer vegetation. None of these hypotheses was supported with nitrogen being immediately taken up by vegetation. It is unclear if longer term study would reveal similar responses.

Nitrogen Fixation Responses in Sphagnum Mosses to N-Additions to an Alberta Poor Fen, 2012-2015

Net N mineralization rates in peat from N-Addition plots in an Alberta Poor Fen, 2011-2014

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 levels <2 kg N ha-1 yr-1. To examine responses to N deposition, over five years, we experimentally applied N (as NH4NO3) to a poor fen near Mariana Lake, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). From 2011 through 2014, we quantified net N mineralization in each plot using the in situ buried polyethylene bag technique. Concentrations of initial KCl-extractable NH4+-N, NO3--N, and DIN in the top 10 cm of peat were unaffected by N inputs. We hypothesized that as N deposition increases to a level that exceeds the capacity of the fen vegetation to take up N, net N mineralization in surface peat would be inhibited by higher NH4+-N availability, net nitrification would be stimulated by higher NH4+-N availability, and concentrations of DIN in porewater at the top of the water table would increase, as DIN bypasses interception by the ground layer vegetation. None of these hypotheses was supported. Experimentally added NH4+-N and NO3--N apparently appear to be rapidly immobilized. This immobilization prevents experimentally added DIN from moving downward through the peat to the bog water table.

Nitrogen Deposition to an Alberta Poor Fen as Measured with Mixed-bed Ion Exchange Resin Tube Collectors, 2011-2015

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 levels <2 kg N ha-1 yr-1. To examine responses to N deposition, over five years, we experimentally applied N (as NH4NO3) to a poor fen near Mariana Lake, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). Resin tubes filled with mixed-bed ion exchange resin were swapped in and out at each collection/deployment date (mid-May and mid-October of each year). Upon collection, resins were extracted with 1M KI and analyzed for inorganic N concentrations. Over all ion exchange resin tube collection dates, deposition of NH4+-N, NO3--N, and dissolved inorganic N (DIN; NH4+-N + NO3--N) averaged 240 ± 29, 318 ± 27, and 557 ± 41 µg m-2 da-1, values that are equivalent to 0.87 ± 0.10, 1.16 ± 0.10, and 2.03 ± 0.15 kg N ha-1 yr-1. While NH4+-N deposition was higher in the growing season than in non-growing season (p = 0.0006), NO3--N deposition was higher in non-growing season than during the growing season (p = 0.0052), with the net result being no seasonal difference in DIN deposition (p = 0.6428).

Vascular Root Biomass and Production at Two Depths in an Alberta Poor Fen Subjected to Increasing Nitrogen Deposition, 2014-2015

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 levels <2 kg N ha-1 yr-1. To examine responses to N deposition, over five years, we experimentally applied N (as NH4NO3) to a poor fen near Mariana Lake, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). From 2014-2015, we examined the effects of N addition on root production by measuring root biomass at two depths and root production over one and two years. Root biomass, measured in 2014, increased with increasing N addition in the 0-15 and 15-30 cm depth increments. Root production increased with increasing N addition in the 0-15 cm, but not the 15-30 cm depth increment; annual root production in the 0-15 cm depth increment was higher when ingrowth bags remained in the peat for two growing seasons, compared to first-year root production. As a result, over the top 30 cm, annual root production was greater when ingrowth bags were in the peat for two growing seasons. We expected a threshold N addition level associated with stimulation of root production but found no evidence of such a threshold at Mariana Lake Poor Fen. Given the rather consistent finding increasing N deposition stimulates aboveground vascular plant biomass and production, and our results that root biomass and production at Mariana Lakes Bog are stimulated as well, further work on belowground responses seems warranted.

Sphagnum fuscum Growth and N Concentration in an Alberta Poor Fen Subjected to Increasing Nitrogen Deposition, 2011-2015

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 levels <2 kg N ha-1 yr-1. To examine responses to N deposition, over five years, we experimentally applied N (as NH4NO3) to a poor fen near Mariana Lake, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). Data collected of the growing season using the crank wire method allowed for the calculation of NPP of the dominant 3 mosses. Tissues were also collected and analyzed for total Nitrogen and Carbon. While we found a modest increase in linear growth and net primary production of S. magellanicum with increasing N addition in three of the 5 years, S. fuscum and S. angustifolium growth were unaffected by N addition. At Mariana Lake Bog, S. fuscum linear growth was unaffected by N addition, although there was evidence for inhibition of NPP S. angustifolium linear growth and NPP were stimulated by fertilization in the first year of fertilization, but by the fourth year fertilization had no effect. Sphagnum capitulum N concentrations were also unaffected by N addition. Given the paucity of data on Sphagnum growth in boreal acidic poor fens, with or without experimental N addition, it is difficult to make generalizations, although it appears that S. fuscum, S. magellanicum, and S. angustifolium responses to increasing N deposition may be species-specific and may differ between bogs and acidic poor fens with much of the N coming from N-fixation.

Peatland Vascular Plant Leaf N Concentrations (5 species) From Leaves collected from N-Addition plots in an Alberta Poor Fen, 2011-2015

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 levels <2 kg N ha-1 yr-1. To examine responses to N deposition, over five years, we experimentally applied N (as NH4NO3) to a poor fen near Mariana Lake, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N ha-1 yr-1, plus controls (no water or N addition). In July of each year, we collected new growth of 5 species of vascular plants, returned them to the lab, cleaned them, dried and ground them, and ran them on a Flash EA 1112 Series CN Soil Analyzer Leaf N concentrations in C. calyculata, A. polifolia, and V. oxycoccos increased significantly with increasing N addition (Fig. 5). For C. calyculata and A. polifolia, there were differences in N concentrations between years, but the regression slopes describing the response to N addition were consistent across all years. Leaf N concentrations were unaffected by N addition for E. vaginatum and S. palustris, with the latter exhibiting interannual differences in leaf N concentrations. Water addition alone had no significant effect on N concentrations for any of the vascular plant species (p >= 0.67).