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.