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How do CAM plants conserve water in desert environments?

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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 (crassulacean acid metabolism) plants conserve water in desert environments primarily through a temporal separation of their photosynthetic processes, which allows them to keep their stomata closed during the heat of the day.12

In these plants, the stomata open only at night when the air is cooler and more humid, minimizing water loss through transpiration. During these nocturnal hours, the plants assimilate carbon dioxide and fix it into organic acids, primarily malate, which is then stored in large vacuoles within the cells.12

During the following daylight hours, the stomata remain closed to prevent water loss. The stored malate is then decarboxylated, releasing the carbon dioxide internally so it can be fixed by the enzyme Rubisco in the Calvin-Benson cycle to produce sugars. By decoupling the uptake of carbon dioxide from the light-dependent reactions of photosynthesis, CAM plants require significantly less water than C3 or C4 plants to achieve the same level of carbon fixation.12