Regional patterns in foliar (15)N across a gradient of nitrogen deposition in the northeastern US.
Recent studies have demonstrated that natural abundance (15)N can be a useful tool for assessing nitrogen saturation, because as nitrification and nitrate loss increase, delta(15)N of foliage and soil also increases. We measured foliar delta(15)N 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 delta(15)N increased from -5.2 to -0.7 per thousand with increasing N deposition from Maine to NY. Foliar delta(15)N decreased between 1987-1988 and 1999, while foliar %N increased and foliar C:N decreased at most sites. Foliar delta(15)N 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.
Pardo
Linda H
LH
USDA Forest Service, Northern Research Station, PO Box 968, Burlington, VT 05402, USA. lpardo@fs.fed.us
McNulty
Steven G
SG
Boggs
Johnny L
JL
Duke
Sara
S
D001061:Appalachian Region; D002980:Climate; D004784:Environmental Monitoring / Q000379:methods; D004785:Environmental Pollutants / Q000032:analysis*; D006801:Humans; D009511:New England; D009584:Nitrogen / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D028222:Picea / Q000254:growth & development; D018515:Plant Leaves / Q000737:chemistry* / Q000254:growth & development; D012987:Soil / Q000032:analysis; D013995:Time; D014197:Trees / Q000254:growth & development*
D004785:Environmental Pollutants; D009587:Nitrogen Isotopes; D012987:Soil; D009584:Nitrogen