Light and Temperature Regulation of Early Morning Crassulacean Acid Metabolism in Opuntia erinacea var Columbiana (Griffiths) L. Benson

During the early morning period, light and temperature exert distinctively different influences on the gas exchange patterns of the Crassulacean acid metabolism plant Opuntia erinacea through their effects on acid metabolism. An initial decrease in CO(2) uptake was triggered by illumination and was apparently due to a decreased CO(2) diffusion gradient through light-mediated decarboxylation of malate. In contrast, the morning burst of CO(2) uptake occurred at high temperature presumably in response to increases in both stomatal conductance and the CO(2) diffusion gradient, resulting from the temperature-regulated fixation of endogenous CO(2), primarily into malate. Subsequent stomatal closure, apparently due to elevated levels of internal CO(2) through rapid decarboxylation of malate at high temperature, was primarily responsible for the final termination of early morning Crassulacean acid metabolism.