Nitrogen Cycling in Pinus banksiana and Populus tremuloides Stands in the Athabasca Oil Sands Region, Alberta, Canada |
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Authors: | Dayna L Laxton Shaun A Watmough Julian Aherne |
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Institution: | (1) Environmental and Life Sciences, Trent University, 1600 West Bank Drive, Peterborough, ON, K9J 7B8, Canada |
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Abstract: | Elevated emissions of nitrogen oxides (NOx) in the Athabasca Oil Sands Region, Alberta and higher foliar nitrogen (N) concentrations in jack pine (Pinus banksiana) needles close to major emission sources has led to concerns that the surrounding boreal forest may become N-saturated. Despite
these concerns, N deposition and impacts on upland forests in the region is poorly quantified. The objective of this study
was to characterize N cycling in five plots representing the two dominant upland forest types (jack pine and trembling aspen,
Populus tremuloides) close (<30 km) to the largest mining operations in the region, during a 2-year period. Despite the high level of NOx emissions, bulk throughfall and deposition measured at both study sites were surprisingly very low (<2 kg N ha−1 year−1). Internal N cycling was much greater in aspen stands; annual N input in litterfall was ten times greater, and net N mineralization
rates were two to five times greater than in jack pine stands. Nitrogen use efficiency (NUE) was much greater in jack pine
when calculated based on N litterfall indices, but not when N pools in biomass were considered. Despite differences in internal
cycling among forest types, nitrate leaching from mineral soil in both forest types was negligible (<0.1 kg N ha−1 year−1) and patterns of 15N in roots, foliage, and mineral soil were typical of N-limited ecosystems, and both sites show no evidence of N saturation. |
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