Plant responses to increased experimental nitrogen deposition in a boreal peatland.

摘要

Increased nitrogen (N) deposition onto boreal peatlands and forests is anticipated with further expansion of Alberta's oil sands industry and consequently, an increase in sources of nitrogen oxide emissions. Increased N deposition has the potential to affect peatland flora and alter N cycling patterns in peatlands, therefore it is imperative to investigate at what level of excess N deposition these effects take place. This thesis discusses results from the first two years of a five year N fertilization study being conducted at a peatland complex near the hamlet of Mariana Lake in northeastern Alberta, Canada aimed at quantifying the N "critical load" for these peatland ecosystems. At the study site there are forty-two experimental plots -- half in an ombrotrophic bog, the other half in the poor fen -- with varying N fertilization treatments ranging from 0 kg/ha/year to 25 kg/ha/year. To investigate nitrogen uptake by plants at the Mariana Lake study site, I measured nitrogen (N) and carbon (C) concentrations of Sphagnum capitulum tissue and vascular plant foliar tissue. For Sphagnum species, I also analyzed C:N ratios and capitulum N storage. To investigate potential growth response of the target Sphagnum species, measurements were taken for linear growth (the vertical elongation of the Sphagnum shoots), stem mass density (the weight of Sphagnum stems occupying a volume after capitula were removed), and ultimately, net primary production (the product of the prior two measurements). Capitulum mass density (biomass) was measured as well to investigate possible changes in Sphagnum capitulum growth. Also, during the height of the growing season (mid-July, 2011 and 2012), the plant communities in each treatment plot were sampled to provide "baseline" data necessary for documenting any shifts in plant distribution or community composition that may occur after N additions.