Water economy and photosynthesis of the CAM plant Senecio medley-woodii during increasing drought

Abstract CO₂ gas exchange, transpiration and water uptake of the succulent Senecio medley-woodii were monitored simultaneously during a 10 day period of increasing drought. The measurements were performed with a combination of a CO₂ gas exchange chamber and a potometer system. Further, leaf water relations and CO₂ gas exchange of a branched potted plant were measured during 15 days of water shortage. The enhancement of CO₂ dark fixation at the beginning of drought modifies the leaf water relations according to the increased malate accumulation during the dark period. The enhancement of water uptake from dusk to dawn corresponds to the increase of Ψ_leaf during the same period. Therefore at the beginning of drought a short time improvement of plant water status through the increased CO₂ dark fixation and malate accumulation can be maintained.