『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 pool
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.
Keywords: Pinus banksiana; Populus tremuloides; nitrogen deposition;
nitrogen saturation; δ15; Forest』
1. Introduction
2. Methods
2.1. Study sites
2.2. Soil sampling
2.3. Nitrogen pools
2.4. nitrogen fluxes
2.5. δ15N natural abundance
2.6. Nitrogen use efficiency
2.7. Calculations and statistical analysis
3. Results
3.1. Nitrogen pools
3.2. nitrogen fluxes and rates
3.2.1. N deposition and leaching
3.2.2. N cycling in aspen and jack pine forests
3.3. δ15N natural abundance
3.4. Nitrogen use efficiency
4. Discussion
4.1. nitrogen deposition
4.2. Nitrogen cycling
4.3. δ15N natural abundance
4.4. Nitrogen use efficiency
5. Conclusion
Acknowledgements
References