Regional patterns in foliar ¹⁵N across a gradient of nitrogen deposition in the northeastern US

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, d¹⁵N of foliage and soil also increases. We measured foliar d¹⁵N 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 d15N increased from 5.2 to 0.7& with increasing N deposition from Maine to NY. Foliar d15N decreased between 1987-1988 and 1999, while foliar %N increased and foliar C:N decreased at most sites. Foliar d15N 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.

Keywords

N saturation, stable isotopes, spruce-fir, northern hardwood forests

Citation

Pardo, Linda H.; McNulty, Steven G.; Boggs, Johnny L.; Duke, Sara. 2007. Regional patterns in foliar 15N across a gradient of nitrogen deposition in the northeastern US. Environmental Pollution, Vol. 149: 293-302