Low nitrogen (N) availability may affect lodgepole pine (Pinus contorta, Pl) and white spruce (Picea glauca, Sw) growth in some reconstructed boreal forest soils in the Athabasca oil sands region in Alberta, Canada. The objective of this study was to investigate the effect of fertilization (N alone or complete fertilizer) on foliar nutrient concentrations in and growth of Pl (planted in soils with tailings sand as a substrate) and Sw (planted in soils with overburden material as a substrate) in a single-tree fertilization study. Two growing seasons after fertilization, both N alone and complete fertilizer treatments increased the height, diameter at breast height and aboveground biomass growth of Sw (p=0.005, 0.009 and 0.015, respectively). In contrast, fertilization did not affect Pl growth. Foliar N concentration and content in current-year needles of Sw were higher following fertilization than in the control treatment in 2012 (p<0.001 for both), but not in 2013. Foliar δ15N in current-year and 1-year-old needles was greater in the fertilization than in the control treatment for Sw (p<0.001 for both), in association with the increase of δ15N in soil NO3--N. No fertilization effect on foliar micronutrients (Fe, Mn, Cu, Zn, B and Mo) or soil NH4+-N, NO3--N or dissolved organic N was found in either Pl or Sw sites. We conclude that N was a limiting factor for tree growth in Sw but not in Pl sites and that N fertilization may be used to improve Sw growth in some reclaimed sites with overburden as a substrate in the oil sands region.