Controls on tropical forest CO2 and energy exchange
Michael
L.
Goulden, University of California at Irvine, Department of Earth System Science, Irvine USA, mgoulden@uci.edu
(Presenting)
Scott
Dennis
Miller, University of California at Irvine, Department of Earth System Science, Irvine USA, sdmiller@uci.edu
Humberto
Ribeiro da
Rocha, DCA/IAG/USP, Universidade de Sao Paulo, humberto@model.iag.usp.br
Christopher
E
Doughty, University of California at Irvine, Department of Earth System Science, Irvine USA, chris_doughty@hotmail.com
Adelaine Michela
e Silva
Figueira, CENA/USP, Santarem, michela@lbaeco.com.br
Helber
Custódio de
Freitas, DCA/IAG/USP, Universidade de Sao, helbercf@model.iag.usp.br
Cleilim
Albert Dias de
Sousa, Universidade Federal do Pará, Santarem, albert@lbaeco.com.br
One of the goals of the Large Scale Biosphere-Atmosphere Experiment in Amazonia is to understand how and why tropical forest CO2 and energy exchange vary diurnally, seasonally, and interannually. Many researchers believe canopy gas exchange is controlled entirely by the interaction between weather (cloudiness, temperature, humidity, rainfall) and plant physiology (photosynthesis, respiration, decomposition). Following this logic, researchers and models attribute an afternoon decline in photosynthesis to the direct effect of increasing evaporative demand on leaf physiology. Similarly, researchers and models attribute a decline in gas exchange during the dry season to the direct effect of drought stress on plant and leaf physiology. While there is little doubt that these biophysical feedbacks are critically important, there is growing evidence that endogenous rhythms in plant physiology also help control tropical forest CO2 and energy exchange. For example, the stomatal conductance and photosynthesis of leaves held in constant irradiance and temperature declines at night and recovers during the subsequent day as a result of an endogenous circadian rhythm. Likewise, the rates of whole canopy gas exchange begin to recover before the dry season ends as a result of an endogenous phenological rhythm. Both of these observations indicate that forest gas exchange is controlled in part by the direct feedback effect of the physical environment, and in part by endogenous, feed-forward mechanisms whereby plants increase or decrease their LAI or photosynthetic capacity in "anticipation" of changes in the physical environment.
Submetido por Michael L. Goulden em 18-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)