Flexibility in CO₂ — Fixation Pathway of a Highland Kalanchoë, Kalanchoë petitiana A. Rich.

Photosynthetic flexibility and water use efficiency of Kalanchoë petitiana A. Rich., a facultative CAM plant endemic to the highlands of Ethiopia, were investigated to determine the physiological determinants for the ecological success of the plant. Both field measurements of δ 13 C and greenhouse gas exchange studies showed a shift from C 3 photosynthesis to CAM as leaves aged or at the onset of water stress. Recycling of CO 2 was observed in developing leaves without concomitant net CO 2 uptake. Accumulation of malate was positively correlated with increased cell sap osmolality and improved daily water use efficiency. The importance of flexibility in carbon uptake pathway and of recycling CO 2 for the ecological success of the plant is discussed.