HR: 1340h
AN: B43A-0143    [Abstracts]
TI: Distribution of Carbon Uptake Capacity of Plant Functional Groups Across the Canopy Gradient in Old-Growth Tropical Wet Forest in Costa Rica
AU: * Oberbauer, S F
EM: oberbaue@fiu.edu
AF: Florida International University, Department of Biological Sciences, Miami, FL 33199 United States
AU: Cruz, H O
EM: harlyn@sloth.ots.ac.cr
AF: Organization for Tropical Studies, La Selva Biological Station, Puerto Viejo, Sar 1 Costa Rica
AU: Ryan, M G
EM: mgryan@fs.fed.us
AF: USDA Forest Service Rocky Mountain Research Station, 240 West Prospect Street, Fort Collins, CO 80526
AU: Clark, D B
EM: dbclark@sloth.ots.ac.cr
AF: University of Missouri-St. Louis, Department of Biology, St. Louis, MO 63121 United States
AU: Clark, D A
EM: daclark@sloth.ots.ac.cr
AF: University of Missouri-St. Louis, Department of Biology, St. Louis, MO 63121 United States
AU: Olivas, P
EM: polivas@sloth.ots.ac.cr
AF: Organization for Tropical Studies, La Selva Biological Station, Puerto Viejo, Sar 1 Costa Rica
AB: Because of the difficulties of accessing leaves within tree crowns, little is known about the photosynthetic capacity of different functional groups within tropical rain forest canopies. To address this deficiency, we measured photosynthetic capacity (A$_{max}$) {\it in situ} along vertical transects through old-growth forest canopy using a mobile walkup tower at the La Selva Biological Station in Costa Rica. We asked: What groups are responsible for most C-fixation and at what height in the canopy does most C-fixation occur? Photosynthesis (using a LI-COR Li-6400) and total leaf area were measured for all vascular plant species encountered within the tower footprint (4.6 m$^{2}$). Plants were grouped into trees, palms, ferns, lianas, epiphytes, herbs, {\it Pentaclethra macroloba} (the dominant canopy tree), and vines. A$_{max}$ values differed among functional groups. The ranking of A$_{max}$ among the groups was trees $>$ {\it P. macroloba} $>$ palms $>$ lianas $>$ vines $>$ epiphytes $>$ herbs $>$ ferns. Trees and {\it P. macroloba} had the highest photosynthetic rates, but the maximum rates occur at different heights. A$_{max}$ of {\it P. macroloba} increases with canopy height to a maximum 10.3 \mumol m$^{-2}$ s$^{-1}$ at 17.5 m. A$_{max}$ of trees increases with canopy height (r$^{2}$ = 0.77) and attains the highest A$_{max}$ at 32.5 m (10.6 \mumol m$^{-2}$ s$^{-1}$). Palms and lianas presented similar patterns of A$_{max}$. However, lianas reach the canopy top whereas palms are shorter and were not observed above 27.5 m. The maximum photosynthetic rates for both groups were: lianas 9.2 \mumol m$^{-2}$ s$^{-1}$ at 27.5 m and palms 9.6 \mumol m$^{-2}$ s$^{-1}$ at 17.5 m. By scaling the functional group A$_{max}$ values with their leaf area, we estimated that most of the photosynthetic capacity occurs between 17.5 m and 37.5 m and is attributed mainly to trees, followed by {\it P. macroloba} and then lianas.
DE: 1851 Plant ecology
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting