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Clusia: CAM photosynthesis

Green leaves act like miniature solar panels. They transform energy from the sun into chemical energy, specifically sugars. These carbohydrates are made form carbon dioxide gas, which is absorbed through tiny pores in the surface of the leaf called stomata. But these pores aren’t one-way paths; water also evaporates through stomata, which could be a problem for plants in hot, dry climates. Fortunately, some plants have developed a special trick: they open their pores only at night when it’s cooler, store carbon dioxide in form of malic acid, and then process it to sugar the following day, when their pores are closed. Though a certain amount of energy is lost through this chemical conversion, this type of photosynthesis has the decisive advantage that it saves water.

This mechanism was first observed in the family of thick-leaved succulents known as Crassulaceae, and is thus known as Crassulacean Acid Metabolism, or CAM for short.

The Clusia in front of you is also capable of CAM photosynthesis. It even has an extra trick: it can turn the CAM mechanism on and off for its indivdual leaves! If a leaf is in direct sunlight, it will use CAM to save water, while a leaf in the shade will operate using normal, more efficient photosynthesis.

Audio file download
Clusia: CAM photosynthesis (MP3, 653 KB)

Audio production and copyright: Soundgarden Audioguidance GmbH
Text: Günter Gerlach, Botanischer Garten München-Nymphenburg

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