Document: JEF-3-59-39

Response of foliar N and P to excessive N deposition in a mid-Appalachian hardwood forest.

MAY, J.D.* ¹, S.B.BURDETTE ¹, F.S.GILLIAM ¹ and M.B.ADAMS ²

Marshall University, Huntington, WV USA ¹
USDA Forest Service, Parsons, WV USA ²

Abstract:
There are increasing concerns about long-term effects of excessive nitrogen (N) deposition on terrestrial ecosystems. While considerable attention has been given to soil responses, there has been relatively little study of the possible responses of plants to N saturation. We studied autumnal N and phosphorus (P) dynamics in foliage of trees on two watersheds supporting stands of similar age at the Fernow Experimental Forest (FEF) in West Virginia: WS3 (fertilized with ammonium sulfate annually since 1989) and WS7 (untreated control). WS3 has previously demonstrated significant evidence of N-saturation. Presenescent and senesced leaves were collected from tulip poplar (Liriodendron tulipifera), black cherry (Prunus serotina), and red maple (Acer rubrum) on each watershed, and analyzed for N and P content. Mean N:P ratios were higher on WS7 for all species, although significantly so only for tulip poplar. Mean foliar N concentration was higher on WS7 for black cherry and red maple, but did not differ for tulip poplar. This contrasts with a 1993 study at FEF in which N concentration in leaves from WS3 was 10% higher for all three species. The change suggests that luxury uptake in the presence of higher available soil N is a transient phenomenon. Nutrient resorption efficiencies during senescence were relatively high for all species on both watersheds-66 to 81% for N and 70 to 82% for P. Mean P resorption did not differ significantly between watersheds. Mean efficiency of N resorption was consistently lower on WS3, although the difference was significant only for black cherry. This may reflect plasticity of resorption in response to reduced N limitation, or altered physiological function resulting from disruption of soil nutrient balances.

Keywords: nitrogen cycling, nitrogen deposition, nitrogen saturation, nutrient resorption

This abstract is being presented at: 4:00 PM in session:
Oral Session #28: Effects of N Deposition in Ecosystems.