PARENT SESSION
Organized Oral Session 31: Structure and function of tropical rainforest canopies
Organizer(s): MG Ryan and DA Clark
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 516 A, Level 5, Palais des congrès de Montréal

Vertical canopy structure in a tropical rain forest: Implications for aboveground plant respiration.

Cavaleri, Molly^*,1, Ryan, Michael^{1, 2}, Clark, David^{3, 4}, Clark, Deborah^{3, 4}, Oberbauer, Steven⁵, Ordonez, Harlyn³, ¹ Colorado State University, Fort Collins, Colorado² Rocky Mountain Research Station USDA Forest Service, Fort Collins, Colorado³ La Selva Biological Station, Puerto Viejo Heredia, Costa Rica⁴ University of Missouri- St. Louis, St. Louis, Missouri⁵ Florida International University, Miami, Florida

ABSTRACT- Tropical rain forests (TRFs) contribute up to one third of the planet's gross primary production, and at least half of the total assimilated carbon in these systems is used in autotrophic respiration. The patterns of TRF autotrophic respiration in relation to vertical light gradients, plant functional groups, foliar nutrients, and woody structure are largely unknown. We measured foliar and woody respiration for over 50 vertical transects from the ground to the canopy top in a primary TRF in Costa Rica. Functional groups included: trees, palms, ferns, epiphytes, herbs, vines, lianas, and Pentaclethra macroloba, a tree species that represents 37% of above-ground biomass. The mean respiration rate per unit leaf area (R_a) was 1.71 ± 0.11 (all errors are SEM) mol m^-2 s^-1 for P. macroloba, which was > 3 times the mean of all other groups. R_a varied with light environment and decreased linearly as the amount of shading from above increased. The mean respiration per unit N (R_N) was similar for all functional groups (347 ± 20 mol kg^-1 N s^-1), and also decreased linearly as the amount of shading from above increased. The mean woody respiration rate (R_W) for P. macroloba (1.46 ± 0.07 mol m^-2 s^-1) was 45% greater than the rates for both trees and lianas, which did not differ significantly. R_W for palms was the lowest of all functional groups (0.53 ± 0.07 mol m^-2 s^-1). R_W of boles measured at the tree base increased 0.02 mol m^-2 s^-1 with each centimeter increase in bole diameter, while R_W of branches higher in the canopy increased 0.03 mol m^-2 s^-1 with each meter of canopy height, regardless of diameter. Understanding these functional group differences and vertical gradients in canopy light environment will improve our ability to scale autotrophic respiration to the canopy in forest process models for this system. Extrapolating canopy woody respiration based only on measurements at the tree base may be underestimating carbon loss.

Key words: foliar respiration, wood respiration, tropical rain forest, canopy structure