PARENT SESSION
Contributed Oral Session 142: Biodiversity and Nitrogen
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal

Host tree vs. vascular epiphyte nutrient concentrations along the Barva Transect, Costa Rica.

Cardelus, Catherine^*,1, Mack, Michelle¹, ¹ University of Florida, Gainesville, FL, USA

ABSTRACT- The degree to which vascular epiphytes are dependent on their host tree for nutrients is unclear. Many have suggested that epiphytes use recycled host tree leaves as a major source of nutrients, particularly N. However, recent evidence supports the notion that epiphyte N sources are independent of host tree foliar chemistry. We found that nutrient concentrations of vascular epiphytes and their host trees were different, as were their patterns of species richness along the Barva Transect (30m-2600m), Costa Rica. Natural abundance ¹⁵N was significantly different between epiphytes and their host trees suggesting that source nutrients between trees and epiphytes is different. Host trees had a more enriched signature suggesting more highly fractionated sources of nitrogen (e.g. forest floor soils), while epiphytes had less enriched signatures suggesting less fractionated sources of nitrogen (e.g. atmospheric deposition and precipitation). Host trees had significantly greater nitrogen content than resident epiphytes showing that N limitation was greater for epiphytes than the host tree. Vascular epiphyte diversity was unimodal along the transect and peaked at 1000m while host tree species richness was also unimodal but peaked at a lower elevation, 300m. When total epiphyte species richness was examined with epiphyte foliar nutrient concentrations, there was a strong linear relationship between species richness and N:P ratio (R² = 0.68, p = 0.02). No relationship was found with host tree nutrients and epiphyte diversity or host tree diversity. These data suggest that vascular epiphytes and canopy trees have different sources of nutrients, particularly N, and that their species richness patterns are governed by different mechanisms.

Key words: Elevational Gradient, Diversity, Stoichiometry, Nitrogen