Ecophysiological response of aspen (Populus tremuloides) and jack pine (Pinus banksiana) to atmospheric nitrogen deposition on reconstructed boreal forest soils in the Athabasca oil sands region

Oil and gas extraction in the Athabasca Oil Sands Region of northeastern Alberta, Canada has increased anthropogenic nitrous oxide (NOx) and ammonia (NH3) emissions over the past three decades, leading to a potential increase in N deposition. Deposition on reclaimed sites was hypothesized to be higher than in surrounding boreal forests, but had not been quantified. The objective of this study was to assess the implications of this potentially increased deposition on reclaimed aspen (Populus tremuloides Michx.) and pine (Pinus banksiana Lamb.) ecosystems through the use of several N status indicators, including N deposition, total and available concentrations in plants and soils, and delta N-15 values in deposition and plants and soils. Atmospheric N deposition, which was dominated by ammonium (NH4+), averaged 24 kg N ha(-1) year(-1) as bulk precipitation and 6 kg N ha(-1) year(-1) as throughfall. Increased N deposition influenced the N cycle in both aspen and pine stands. Aspen appeared to be actively biocycling N as indicated by a closed N cycle, resulting in minimal N losses. Whereas the N cycle in pine may be more open as indicated by the dominance of soil nitrate (NO3-), and enrichment of N-15 in available soil NH4+, root and foliar N. Therefore, we suggest that pine stands on reclamation sites may be at kinetic N saturation where the rate of N inputs exceeds vegetation and soil N net sinks, and do not require additional N fertilizer inputs. (C) 2019 Elsevier B.V. All rights reserved.