Respuesta fotosintética de Coffea arabica a diferentes niveles de luz y disponibilidad hídrica

Shading would allow a better acclimation of coffee plants in response to winter conditions where the nights are relatively cool followed by sunny, warm days and summer conditions with high temperature and rain, in southeastern Brazil. This study aimed to explore the effects of contrasting light conditions combined with two levels of available soil water on water relations and photosynthesis in Coffea arabica L. plants under winter and summer conditions. In both seasons, decreases in photosynthetic rates (A), stomatal conductance (gs) and Ci/Ca ratio were found in droughted plants grown in both the shade and full sun. These changes were accompanied by decreases in transpiration rate and hydraulic conductance. There were no differences in the quantum efciency of electron transport by photosystem II (PSII), nonphotochemical quenching and non-regulated non-photochemical energy loss in PSII. Compared to shade grown plants, sun-grown plants showed lower A, gs and Ci/Ca ratio under winter conditions. The decrease in the variable-to-initial chlorophyll uorescence ratio suggests that photochemical events played a role in limitating photosynthesis. The results suggest that any recommended as a cultural management practice should be considered with reserve.