Cactus
Adaptations for water conservation
Crassulacean acid metabolism (CAM) is a mechanism adopted by cacti and other succulents to avoid the problems of the C3 mechanism. In full CAM, the stomata open only at night, when temperatures and water loss are lowest. CO 2 enters the plant and is captured in the form of organic acids stored inside cells (in vacuoles). The stomata remain closed throughout the day, and photosynthesis uses only this stored CO 2. CAM uses water much more efficiently at the price of limiting the amount of carbon fixed from the atmosphere and thus available for growth. CAM-cycling is a less efficient system whereby stomata open in the day, just as in plants using the C3 mechanism. At night, or when the plant is short of water, the stomata close and the CAM mechanism is used to store CO 2 produced by respiration for use later in photosynthesis. CAM-cycling is present in Pereskia species.
Cactus-35