How do CAM plants avoid photorespiration?

CAM (Crassulacean Acid Metabolism) plants have developed a unique adaptation that helps them avoid photorespiration, an inefficient process that can occur in plants when the enzyme RuBisCO binds to oxygen instead of carbon dioxide. The key to how CAM plants minimize photorespiration lies in their ability to separate the processes of carbon fixation and the Calvin cycle temporally.

During the night, CAM plants open their stomata to take in carbon dioxide. This carbon dioxide is fixed into organic acids, primarily malate, and stored in vacuoles. When daytime arrives, the stomata close to conserve water, a critical adaptation for many CAM plants that thrive in arid environments. The stored malate is then converted back into carbon dioxide for use in the Calvin cycle, which occurs during daylight when photosynthesis can take place.

This temporal separation allows CAM plants to utilize carbon dioxide without the risk of losing water through open stomata in the heat of the day, significantly reducing the likelihood of photorespiration. Therefore, the ability to carry out these processes at different times is the most accurate reason for how CAM plants avoid photorespiration.