Anatomical and physiological plasticity of leaves of Coffea arabica L. in response to irradiance / Plasticidade anatômica e fisiológica de folhas de Coffea arabica L. em resposta à irradiância

AUTOR(ES)

Fábio Santos Matos

DATA DE PUBLICAÇÃO

2008

RESUMO

Morphological, physiological and biochemical parameters were examined in coffee leaves from different canopy positions. Four classes of leaves were chosen based on the mean diurnal intercepted photosynthetically active radiation. These classes (treatments) comprised leaves intercepting 30, 75, 300, 750 μmol photons m-2 s-1, hereafter referred to T1, T2, T3, and T4, respectively. Morphologically, the single leaf area, and particularly the specific leaf area (SLA), increased in leaves under deep shade. Compared to sunlit leaves, shade leaves showed less differentiated palisade and spongy parenchyma with greater abundance of intercellular spaces, leading to thinner and less dense leaves with a higher SLA. The net carbon assimilation rate decreased with decreasing light availability, from 7.2 (T4) to 2.3 (T1) μmol (CO2) m-2 s- 1. The compensating irradiance was on average 88% higher in T3 and T4 leaves as compared with T1 and T2 leaves. The smaller chlorophyll concentration in T4 leaves relative to T1 leaves should have led to a lower leaf absorptance and, thus, leading to reduced amount of energy actually absorbed by the photosystems. Sunlit leaves showed greater concentration of xanthophylls (violaxanthin + antheraxanthin + zeaxanthin) and higher values of deepoxidation state of xanthophylls, indicating a greater capacity for energy dissipation in these leaves than in shaded leaves. Changes in maximum rate of carboxylation limited by rubisco, in maximum rate of carboxylation limited by the electron transport and in net assimilation rate of CO2 under elevated CO2 were minimal, if any, amongst the leaves examined here. Results suggest that coffee leaves display some morphophysiological traits with adequate phenotypic plasticity allowing the coffee tree to adjust itself to the light availability. However, the capacity of acclimation to irradiance seems to occur at the expense of an inefficient allocation of resources, such as nitrogen.

ASSUNTO(S)

café pigmentos coffee pigments physiology fisiologia vegetal fisiologia

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