PARENT SESSION
Organized Oral Session 48: Nitrogen cycling in terrestrial ecosystems: New insights from isotopes and experiments
Organizer(s): MC Mack, P Templer, and K Nadelhoffer
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 510b, Level 5, Palais des congrès de Montréal

Effect of tree species and nitrogen fertilization on nitrogen retention in the Catskill Mountains, New York.

Templer, Pamela¹, Lovett, Gary², Weathers, Kathleen², Findlay, Stuart², Dawson, Todd¹, Arthur, Mary³, ¹ University of California Berkeley, Berkeley, CA, USA² Institute of Ecosystem Studies, Millbrook, NY, USA³ University of Kentucky, Lexington, KY, USA

ABSTRACT- This study examined the effect of four tree species and nitrogen (N) fertilization on N retention within forested areas of the Catskill Mountains, New York. We conducted a ¹⁵N field tracer experiment to determine how N moves through soil, microbial, and plant pools under different tree species and N fertilization regimes. Samples were collected from single species plots of American beech (Fagus grandifolia Ehrh.), eastern hemlock (Tsuga canadensis L.), red oak (Quercus rubra L.), and sugar maple (Acer saccharum Marsh) 300 days and 3 years after ¹⁵N addition. Using paired plots we compared the ¹⁵N recovery in plots that received ambient levels of N inputs (11 kg N / ha / yr) to plots that received additions of 50 kg N/ ha / yr. Total plot ¹⁵N recovery (litter layer, organic and mineral soil to 12 cm, fine roots and aboveground biomass) did not vary significantly among tree species, but the distribution of sinks for ¹⁵N within the forest ecosystem did vary. Recovery in the forest floor was significantly lower in sugar maple stands compared to the other species. ¹⁵Nitrogen recovery was significantly lower in the fertilized plots compared to the ambient plots and red oak stands had the largest drop in ¹⁵N recovery as a result of N fertilization. Aboveground biomass became a significantly greater ¹⁵N sink with fertilization, although it retained less than 1% of the tracer addition. These results indicate that different forest types vary in the amount of N retention in the forest floor, and that forest N retention may change depending upon N inputs.

Key words: forest ecosystem, nitrogen saturation, stable isotope