PARENT SESSION
Oral Session # 35: Biogeochemistry III: Arctic, Alpine, and Tundra Systems.
Presiding: A Hartley
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 203.
Effects of N deposition on high elevation forests in the northeastern US: foliar 
15N patterns.
Pardo, Linda*,1, McNulty, Steven2, Boggs, Johnny2, 1 USDA Forest Service, Burlington, VT2 USDA Forest Servce, Raleigh, NC
ABSTRACT- Recent studies have demonstrated that natural abundance of 15N can be a useful tool for assessing N saturation, because as nitrification and nitrate loss increase, 15N of foliage and soil also increases. In this study, we measured foliar 15N at eleven high elevation spruce-fir stands along a N deposition gradient from Maine to New York in 1987-88 and from seven paired northern hardwood and spruce-fir stands in 1999. In 1999, foliar 15N in the spruce-fir stands ranged from −5.2 to −0.7‰ while foliar C:N ranged from 52 to 30 with increasing N deposition from Maine to NY. Foliar 15N in the hardwood stands was on average 1‰ higher than the spruce-fir foliage, and ranged from −4.2 to −0.5‰ with increasing deposition. Hardwood foliar C:N ranged from 28 to 16 along the gradient. No changes were observed in foliar d15N between 1987 and 1999, however foliar %N increased and foliar C:N decreased at all sites except the site receiving the lowest deposition (Howland Forest in Maine). Additional measurements included soil C:N and base cations, net mineralization and nitrification potential, basal area, and seedling regeneration. Foliar 15N was correlated most strongly with N deposition, and was also positively correlated with net nitrification potential and negatively correlated with soil C:N ratio. The spruce-fir foliar 15N values at the upper end of the deposition gradient approach values observed at a site (Mt Ascutney, VT) where foliar 15N went from −3.5 to +0.5‰ as the site reached N saturation. This study allowed us to evaluate ecosystem response to different levels of N deposition.
Key words: 15N, N saturation, foliar nutrients, N deposition