What roles do C4 and CAM photosynthesis play in Caryophyllales plants?

Within the diverse order Caryophyllales, many species have evolved specialized physiological adaptations to thrive in challenging, arid, or salty environments. Among these are the C4 and CAM (crassulacean acid metabolism) photosynthetic pathways, which help plants minimize water loss and improve carbon fixation efficiency.1

C4 Photosynthesis

C4 plants utilize a spatial separation of carbon fixation to suppress photorespiration, a process that otherwise reduces photosynthetic efficiency in warmer climates. In these plants, carbon dioxide is initially fixed in the mesophyll cells into a four-carbon acid, which is then transferred to bundle-sheath cells to be released and processed by the Calvin-Benson cycle. This mechanism allows the plant to maintain high internal CO2 concentrations, enabling it to keep its stomata less open and thereby conserve water.23

CAM Photosynthesis

CAM photosynthesis involves a temporal separation of carbon fixation. Members of the order that use this pathway, such as those in the families Cactaceae, Portulacaceae, and Basellaceae, open their stomata at night to collect CO2, which is stored as malic acid in cell vacuoles. During the day, the stomata close to prevent water loss, and the stored acid is processed to release CO2 for the Calvin-Benson cycle. This adaptation is particularly effective for survival in hot, dry environments.4526