Britannica Sources used in this answer

Why do CAM plants open their stomata at night?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals. — photosynthesis Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide.

CAM plants open their stomata at night primarily to conserve water in arid environments. By keeping their stomata closed during the hot daylight hours, these plants significantly reduce water loss through transpiration.12

Because the air is cooler and more humid at night, it is an ideal time for these plants to assimilate carbon dioxide without risking excessive dehydration. During these nocturnal hours, CAM plants fix carbon dioxide into organic acids, such as malate, which are then stored in the vacuoles of their cells.12

During the day, the stomata remain closed, and the stored malate is released and decarboxylated to provide a high concentration of carbon dioxide for the Calvin-Benson cycle. This temporal separation of carbon fixation stages allows CAM plants to thrive in environments where water is scarce.12