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CAM plants have a unique adaptation when it comes to stomatal activity. Unlike most plants that open their stomata during the day for photosynthesis, CAM plants do the opposite. They open their stomata at night. This nighttime activity is crucial because it helps minimize water loss. When the stomata open at night, cooler temperatures and increased humidity lead to less water being lost through transpiration. By opening their stomata in the dark, CAM plants allow carbon dioxide to enter and be fixed into organic acids, primarily malate. This malate is then stored in vacuoles until it can be utilized in the light-dependent reactions during the day when the stomata are closed, making this process incredibly water-efficient.

The carbon fixation pathway of CAM plants is distinct from that of typical C3 plants. Instead of initially creating a 3-carbon molecule during carbon fixation, CAM (and C4) plants fix carbon dioxide into 4-carbon compounds such as oxaloacetate at night. This process differs significantly from the C3 pathway, where the first stable product is 3-phosphoglycerate, a 3-carbon molecule. The conversion of carbon dioxide into a 4-carbon compound allows CAM plants to store carbon internally at night, which is then released throughout the day to power the Calvin cycle without direct gas exchange with the environment.

In CAM plants, the Calvin cycle is an essential part of the photosynthetic process but operates differently compared to C4 plants. During the daytime, when the stomata are closed, CAM plants utilize the previously stored carbon dioxide from organic acids to drive the Calvin cycle in all mesophyll cells. This cycle does not take place specifically in bundle sheath cells, as it does in C4 plants. The Calvin cycle in CAM plants relies on the internal CO2 concentration to synthesize glucose from carbon dioxide. This daytime activity does not require the stomata to be open, thus conserving water and valuable resources.

Photorespiration is a process that can limit photosynthesis by wasting energy and reducing the plant's efficiency in utilizing light energy. However, CAM plants have a robust mechanism to minimize photorespiration. By opening their stomata at night, CAM plants can maintain high concentrations of carbon dioxide, which minimizes the occurrence of photorespiration. Because photorespiration primarily occurs when oxygen is fixed instead of carbon dioxide, the strategy of night-time stomata opening in CAM plants keeps the photosynthetic machinery operating more efficiently compared to many C3 plants. This adaptation makes CAM plants better suited to arid environments where water conservation is critical.

The water efficiency of CAM plants is one of their most remarkable traits. CAM plants showcase an exceptional ability to conserve water during photosynthesis. This efficiency arises from their stomatal behavior—opening at night when evaporation rates are lower, and humidity levels are higher. By closing their stomata during the day, they drastically reduce water loss even under intense sunlight. This adaptation allows CAM plants not only to survive but thrive in harsh, dry environments where other plants might struggle. Their photosynthetic process optimally balances the need for carbon fixation and water conservation, making them masters of survival in water-limited conditions.