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

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.