Document: GAR-3-59-58

Effect of tree species on nitrogen cycling in the Catskill Mountains, NY: Fertilization studies.

LOVETT, G.M.* ¹, K.C.WEATHERS ¹ and M.A.ARTHUR ²

Institute of Ecosystem Studies, Millbrook, NY 12545 ¹
University of Kentucky, Lexington, KY 40546 ²

Abstract:
Nitrate concentration in stream water varies 18-fold among small, forested watersheds in the Catskill Mountains, NY. Part of that variation appears to be attributable to differences in tree species composition in the watersheds. In particular, our sampling shows that watersheds with a significant percentage of oak in the forest typically have low (< 10 micromolar) nitrate concentrations throughout the year. We established 30 pairs of single-species plots to study N cycling associated with the five major tree species of the Catskills. One plot of each pair is fertilized with 50 kg N/ha/y, while the other plot is unfertilized. We find highly significant (p<0.0001) differences among species in potential N mineralization and nitrification rates, with northern red oak having particularly low rates of potential nitrification. Preliminary results from fertilized plots indicate that N fertilization increases nitrification rates (relative to control plots) in species with low-lignin foliage, such as sugar maple (control vs. fertilized p=0.017), but decreases nitrification rates in high-lignin species like red oak (p<0.0001) and American beech (p<0.0001). These results suggest that forest species composition may partially control N retention by forested watersheds, and that different forest types may respond in a qualitatively different manner to excess nitrogen loading from the atmosphere.

Keywords: nitrogen, tree species, oaks, nitrification

This abstract is being presented at: 10:45 AM in session:
Oral Session #41: N Dynamics: Additions, Retention and Transformations.