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 NH 4 NO 3 ) 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.