Regional patterns in foliar 15N across a gradient of nitrogen deposition in the northeastern US.
Authors:
Pardo, L.H. McNulty, S.G. Boggs, J.L. Duke, S. USDA, ARS
Source:
Environmental pollution. 2007 Oct., v. 149, issue 3, p. 293-302.
NALT Subjects:
leaves bioaccumulation air pollution atmospheric deposition stable isotopes nitrogen nitrification conifer needles forest stands biogeochemical cycles soil pollution forest soils altitude forest trees Picea Abies hardwood forests carbon nitrogen ratio coniferous forests forest litter Northeastern United States
Issue Date:
Oct-2007
Abstract:
Recent studies have demonstrated that natural abundance 15N can be a useful tool for assessing nitrogen saturation, because as nitrification and nitrate loss increase, δ15N of foliage and soil also increases. We measured foliar δ15N at 11 high-elevation spruce-fir stands along an N deposition gradient in 1987-1988 and at seven paired northern hardwood and spruce-fir stands in 1999. In 1999, foliar δ15N increased from -5.2 to -0.7[per thousand] with increasing N deposition from Maine to NY. Foliar δ15N decreased between 1987-1988 and 1999, while foliar %N increased and foliar C:N decreased at most sites. Foliar δ15N was strongly correlated with N deposition, and was also positively correlated with net nitrification potential and negatively correlated with soil C:N ratio. Although the increase in foliar %N is consistent with a progression towards N saturation, other results of this study suggest that, in 1999, these stands were further from N saturation than in 1987-1988. Foliar δ15N increased with increasing N deposition from Maine to NY, but decreased between 1987-1988 and 1999
