Variations canopy leaf temperature and effects on co2 assimalation rate at Central Amazon. / Variações da temperatura foliar do dossel e o seu efeito na taxa assimilatória de CO2 na Amazônia Central.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The role of the Amazon Rain Forest in the carbon budget has been often reported, however little is known about the aspects regulating the processes of carbon assimilation and its release from the biosphere to the atmosphere. The objective of this work was to describe the responses of respiration and photosynthesis processes related to leaf temperature variations by using biophysics characteristics and micro-meteorological data in order to predict CO2 assimilation rates on individual or community level. The research was conducted at the Experimental Station for Tropical Forest research (ZF-2) of the National Institute of Research of the Amazon (INPA). For this study four towers were used to access the canopy. Climatic parameters were monitored by micrometeorological stations Li-1401. The leaf temperature was measured using copper-contantan thermocouples. Photosynthesis and respiration were evaluated with an infra-red gas analyzer, generating light and CO2 curves responses. The results showed that: the leaf temperature was related to the photosynthetic active radiation (PAR) and to the relative air humidity (UR). The optimal photosynthesis temperature was 31,1 ºC where the tree community presented 7,6 µmol.m-2.s-1 of net CO2 assimilation. Above this temperature a reduction of the maximal photosynthesis was determined. Leaf temperatures higher than 34,0 ºC decreased the maximal velocity of RuBP carboxilation and temperatures higher than 35,7ºC decreased the maximal capacity of electrons transportation. The stomatal conductance decreased with increasing leaf temperatures within the temperature interval studied. The results indicated that the stomatal limitation probably represent the main factor that effects photosynthesis. The respiration contributes to reduce the carbon assimilation due to the increase of the leaf temperature because respiration is positively related to leaf temperature. Thus, the CO2 assimilation rates decreased with an increase of leaf temperature and is mainly affected by a decrease of stomatal and mesophyll conductance and by an increase of leaf respiration.

ASSUNTO(S)

floresta tropical (botanic) forest canopy fotossíntese amazônia central leaves temperatura – variação carbon gas tropical rain forest photosynthesis folhas central amazon dossel (botânica) temperature gás carbono

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