Regional assessment of N saturation using foliar δ15N

Pardo L.H. 1, Templer P. 2, Goodale C.L. 3, Duke S. 4, Groffman P. 5, Adams M.B. 6, Boeckx P. 7, Boggs J. 8, Campbell J. 9, Colman B. 10, Compton J. 11, Emmett B. 12, Gundersen P. 13, Kjønaas J. 14, Lovett G. 5, Mack M. 15, Magill A. 16, Mbila M. 17, Mitchell M.J. 18, McGee G. 18, McNulty S. 8, Nadelhoffer K. 19, Ollinger S. 16, Ross D. 20, Rueth H. 21, Rustad L. 9, Schaberg P. 1, Schiff S. 22, Schleppi P. 23, Spoelstra J. 22, Wessel W. 24

1 Northeastern Research Station, USDA Forest Service, P.O. Box 968, Burlington, VT 05402, USA
2 Department of Biology, Boston University, Boston, MA 02215, USA
3 Dept. of Ecology & Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
4 Agricultural Research Service, College Station, TX 77845, USA
5 Institute of Ecosystem Studies, Millbrook, NY 12545, USA
6 USDA Forest Service, Parsons, WV 26287-0404, USA
7 University of Ghent, B-9000 Gent, Belgium
8 USDA Forest Service, Raleigh, NC 27606, USA
9 USDA Forest Service, Durham, NH 03824-0640, USA
10 University of California, Santa Barbara, CA 93106-9610, USA
11 US Environmental Protection Agency, Corvallis, OR 97333-4902, USA
12 Centre for Ecology and Hydrology, Bangor LL57 2UP, UK
13 Danish Centre for Forest, Landscape and Planning, KVL, DK-2970 Hørsholm, DK
14 Norwegian Forest Research Institute, N-1432 Aas, Norway
15 University of Florida, Gainesville, FL 32611, USA
16 University of New Hampshire, Durham, NH 03824, USA
17 Alabama A&M University, Normal, AL 35762, USA
18 SUNY School of Environmental Science and Forestry, Syracuse, NY 13210, USA
19 The University of Michigan, Ann Arbor, MI 48109-1048, USA
20 University of Vermont, Burlington, VT 05405, USA
21 Grand Valley State University, Allendale, MI 49401, USA
22 University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
23 Swiss Federal Institute for Forest, Snow and Landscape Research, CH-8903 Birmensdorf, Switzerland
24 University of Amsterdam, 1018 WV Amsterdam, Netherlands

Biogeochem. 80 (2006): 143-171

DOI: 10.1007/s10533-006-9015-9


N saturation induced by atmospheric N deposition can have serious consequences for forest health in many regions. In order to evaluate whether foliar δ15N may be a robust, regional-scale measure of the onset of N saturation in forest ecosystems, we assembled a large dataset on atmospheric N deposition, foliar and root δ15N and N concentration, soil C:N, mineralization and nitrification. The dataset included sites in northeastern North America, Colorado, Alaska, southern Chile and Europe. Local drivers of N cycling (net nitrification and mineralization, and forest floor and soil C:N) were more closely coupled with foliar δ15N than the regional driver of N deposition. Foliar δ 15N increased non-linearly with nitrification:mineralization ratio and decreased with forest floor C:N. Foliar δ15N was more strongly related to nitrification rates than was foliar N concentration, but concentration was more strongly correlated with N deposition. Root δ15N was more tightly coupled to forest floor properties than was foliar δ15N. We observed a pattern of decreasing foliar δ15N values across the following species: American beech > yellow birch > sugar maple. Other factors that affected foliar δ15N included species composition and climate. Relationships between foliar δ15N and soil variables were stronger when analyzed on a species by species basis than when many species were lumped. European sites showed distinct patterns of lower foliar δ15N, due to the importance of ammonium deposition in this region. Our results suggest that examining δ15N values of foliage may improve understanding of how forests respond to the cascading effects of N deposition.

Keywords: 15N, fine roots, forests, N deposition, natural abundance