Poster: Ecophysiology

Abs # 46: Effects of nitrogen addition to the canopy at Howland Forest, ME and to the forest floor at Harvard Forest, MA on the foliar physiology and forest productivity.

Presenter:	Minocha, Rakesh , rminocha@hopper.unh.edu
Authors	Minocha, Rakesh  (A)   Hollinger, David  (A)   Long, Stephanie  (A)   Dail, Bryan  (B)   Magill, Alison  (C)   Aber, John D. (C)
Affiliations:	(A): USDA Forest Service, NERS, Durham, NH, USA (B): University of Maine, Department of Plant, Soil, and Environmental Sciences, Orono, ME, USA (C): University of New Hampshire, Complex Systems Research Center, Durham, NH, USA

Atmospheric nitrogen (N) deposition may cause forest decline or enhance its productivity depending on the initial N status of the soil, and the rate and duration of N deposition. Continuous deposition of N can move ecosystems towards nitrogen saturation. Previous studies from our group show a strong correlation between soil nutrient deficiencies and/or chronic N addition and increased foliar free putrescine (an organic polyamine) levels, indicating that foliar putrescine can potentially be used as a marker of general stress in visually healthy trees. Free amino acids, especially arginine, also increased in response to chronic N input. The objective of the present study was to determine changes in foliar physiology (cellular polyamines, amino acids, proteins and chlorophyll levels) at the Howland Experimental Forest following a relatively low level of nitrogen application to canopy (18 Kg N ha ^-1 y^-1) since 2001 and at the Harvard Forest LTER Site where a similar experiment underway since 1989 is adding 50 and 150 Kg N ha^-1 y^-1 of N to the forest floor. We predicted that at the Howland site, the smaller foliar N addition will not exceed the capacity for N uptake by vegetation and may lead to greater C sequestration. This is unlikely to put physiological stress on trees. Our preliminary data for first two years at Howland show no change in the physiology of the needles due to canopy N application. However, significant changes in foliar physiology were observed after 6 years of chronic N addition at Harvard Forest. The long-term goal is to be able to better understand the N deposition levels that elicit a physiological stress response in a forest where N availability is assumed to limit net primary productivity.