Biological N2-fixation in Boreal Peatlands of Alberta Canada Following Acute N-Deposition: Down-Regulation and Subsequent Post-Recovery Projections.

Abstract:

Globally, boreal peatlands cover a mere 3-4 % of the Earth’s land surface, yet store ~ 30% of the world’s soil carbon and ~9-16% of global soil nitrogen. Biological N₂-fixation is the primary input of new nitrogen (N) to bogs in Alberta. We have demonstrated that this process is down regulated in the presence of enhanced atmospheric N deposition such as that from the growing Oil Sands Mining Operations in northern Alberta Canada. An important question for understanding the long term function of bogs in Alberta is whether N₂-fixation can recover upon cessation of N pollution, and if so, how quickly? Here we present our preliminary findings in pursuit of this question. We measured rates of biological N₂-fixation using the acetylene reduction assay (ARA), with subsequent calibration using ¹⁵N₂ on separate, but paired incubations. Sphagnum fuscum from bogs at two different sites from northern Alberta were incubated over the course of 3 years, in 3 experimentally added treatments in the field; controls, plots receiving no added N and no water, water only treatments (no added N), and plots that were fertilized with N at a rate of 20 kg·ha^-1·yr^-1, and plots which had been fertilized with 20 kg·ha^-1·yr^-1in 2012-2013, but not since. In 2014, the rates of N₂-fixation in the 20 kg·ha^-1·yr^-1plots and the recovering 20 kg·ha^-1·yr^-1plots were not significantly different, but both were significantly lower than the controls (p<0.05). In 2015, control plots had significantly higher rates of N₂-fixation than the plots that had previously received 20 kg·ha^-1·yr^-1 in 2012 and 2013, and the plots that had not received 20 kg·ha^-1·yr^-1 since 2013 had significantly higher rates of biological N₂-fixation. These data suggest that in a low atmospheric N deposition scenario, and over a short time frame, peatlands of northern Alberta may be able to recover from chronic atmospheric N deposition.