In a desert plant, carbon dioxide is taken in at night and stored as an intermediate, which is later used during the day for carbohydrate synthesis. What advantage does this adaptation provide to the plant in its environment?
It reduces water loss by stomatal opening to cooler night hours
The plant described follows Crassulacean Acid Metabolism (CAM), a photosynthetic adaptation found in many desert plants such as cacti and Kalanchoe. In CAM plants the stomata stay closed during the hot, dry day and open at night, when the air is cooler and more humid. Carbon dioxide taken up at night is fixed as an organic acid (usually malic acid) and stored in the vacuole. During the day, when light is available for the light reactions, the stored acid releases CO2 for the Calvin cycle even with the stomata closed.
The main advantage of opening stomata only at night is a large reduction in transpirational water loss, which is critical in dry desert conditions. It does not eliminate the need for chlorophyll or restrict carbohydrate synthesis to the night; carbohydrate synthesis still needs sunlight and happens during the day. The rate of photosynthesis in CAM plants is actually lower than in normal C3 plants; water conservation, not speed, is the point.
Hence, the answer is It reduces water loss by stomatal opening to cooler night hours.
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