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
Foliar nutrients and 15N in tropical forests: From Hawaii to the continents.
Vitousek, Peter*,1, Martinelli, Luiz 2, Nardoto, Gabriela 2, Townsend, Alan3, 1 Stanford University, Stanford, CA2 University of Sao Paulo, Piracicaba, Brazil3 University of Colorado, Boulder, CO
ABSTRACT- We collected information on N-15 and foliar nutrient concentrations in the dominant tree Metrosideros polymorpha in 90 sites across the Hawaiian archipelago, with annual precipitation ranging from 500 to 5500 mm/yr and substrate age from 120 to 4,100,000 years. Foliar 15N ranged from -8.3 to +5.1 per mil, and was inversely correlated with annual rainfall. At a given rainfall, sites on young soils were relatively depleted in 15N, and intermediate-aged sites with fertile soils were relatively enriched; forests on highly weathered, strongly nutrient-depleted soils had intermediate 15N. Additional species (other than putative N-fixers) followed patterns similar to those for Metrosideros. Average 15N values for canopy trees drawn from a large data set of diverse continental tropical forests yielded similar patterns; foliar 15N is positively correlated with the length of the dry season in the Brazilian Amazon, and forests on fertile soils are enriched in 15N relative to those on poorer soils. These patterns could results from differences in plant versus soil 15N, from differences in the openness of the N cycle (the magnitude of inputs and outputs versus the quantity of N within systems), or from differences in fractionation during N loss. We suggest that differences in the relative openness of the N cycle contribute most strongly to fertility-related variation in foliar N-15, while differences in fractionation during output contribute more strongly to rainfall-associated variation.
Key words: Nitrogen-15, Hawaii, Tropical forest