Regional Assessment of N Saturation using Foliar and Root δ15N
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 δ15N 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.
Digital Object Identifier (DOI)
Pardo, L.H., P. Templer, C.L. Goodale, S. Duke, P. Groffman, M.B. Adams, P. Boeckx, J. Boggs, J. Campbell, J. Compton, B. Emmett, P. Gundersen, J. Kjønaas, G. Lovett, M. Mack, A. Magill, M.J. Mitchell, M. Mbila, G. McGee, S. McNulty, K. Nadelhoffer, B. Colman, S.V. Ollinger, D. Ross, H. Rueth, L. Rustad, P. Schaberg, S. Schiff, P. Schleppi, J. Spoelstra, W. Wessel. 2006. Regional Assessment of N saturation using foliar and root δ15N. Biogeochemistry, 80 (2): 143-171.
© Springer 2006