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Determining Responses of Tropical Rain Forest Canopy Photosynthesis to Changes in Cloud Cover: A Bottom-Up Approach

EPA Grant Number: U915021
Title: Determining Responses of Tropical Rain Forest Canopy Photosynthesis to Changes in Cloud Cover: A Bottom-Up Approach
Investigators: Vierling, Lee A.
Institution: University of Colorado at Boulder
EPA Project Officer: Broadway, Virginia
Project Period: January 1, 1996 through April 13, 1999
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1996)
Research Category: Academic Fellowships , Fellowship - Ecology and Ecosystems , Ecological Indicators/Assessment/Restoration

Description:

Objective:

The objectives of this research project are to: (1) determine how variations in cloud cover impact tropical rain forest canopy light and temperature environments; and (2) how these changes may influence photosynthesis at the canopy scale.

Approach:

This research project integrates three main sources of information: field studies, greenhouse experiments, and simulation modeling. Field measurements were taken during November and December of 1996, within a monospecific (Gilbertiodendron dewrevrei) primary rain forest located in the Republic of Congo, Central Africa. In the field, cloud cover was quantified by continuously measuring the sky diffuse fraction from atop a tower extending above the canopy. Simultaneously, a suite of physical and ecophysiological measurements was gathered at various depths throughout the canopy. These measurements included detailed quantification of photosynthetically active radiation, leaf temperature, leaf area index, and leaf angle distribution. In addition, in situ measurements of leaf photosynthesis with varying light, temperature, and intercellular CO2 were made using a portable photosynthesis instrument. To supplement these field data, measurements of photosynthetic activity from Gilbertiodendron saplings will be made in the greenhouse. A system will be developed to expose the saplings to light and temperature environments similar to those measured in the field. A critical greenhouse measurement will be to quantify photosynthetic induction, a phenomenon that controls the carbon economy of a leaf during lightflecks. The modeling component of this research project will synthesize field and greenhouse measurements to arrive at a multiple-layer representation of canopy photosynthesis under various cloud conditions. This model hopefully will be validated in the future with tower eddy covariance measurements of CO2 flux.

Supplemental Keywords:

fellowship, tropical rain forest, forest canopy, photosynthesis, cloud cover, photosynthetic activity, leaf area index, leaf temperature, leaf angle distribution.

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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