High productivity and photosynthetic flexibility in a CAM plant.

In the annual succulent Mesembryanthemum crystallinum growing in situ, the balance between C3 and CAM carbon fixation shifted rapidly in response to changes in water availability. When water was plentiful, M. crystallinum fixed carbon dioxide by the C3 pathway and grew at rates comparable to other C3 species. Under drought conditions, M. crystallinum fixed carbon by the CAM pathway at an average rate which exceeded 1 nanomole of carbon dioxide per square centimeter of leaf surface per second, a very high rate for a CAM plant.