Drought Stress Response in Carpobrotus edulis: Sharing or Saving Resources

RM 210

This work examined the role of alternative drought tolerance mechanisms in the succulent ground cover plant, Carpobrotus edulis. C. edulis produces new plants (ramets) which are physically connected by stolons. It is a major invasive plant in coastal California. Previous studies demonstrate the ability of C. edulis to switch from C3 to Crassulacean Acid Metabolism (CAM) photosynthesis, allowing the plant to save water under drought conditions. As well, previous studies have shown improved performance in C. edulis stolon connected ramets. Presumably, this improved performance occurs through sharing resources like water. We were interested in whether water conservation through CAM induction or water sharing through connected ramets was an alternative or complementary response for drought tolerance. We grew 96 potted C. edulis ramets divided into four treatments, connected watered (CW), connected droughted (CD), severed watered (SW) and severed droughted (SD), in controlled greenhouse conditions. We measured air and leaf temperature, titratable acidity, pre-dawn leaf water status, leaf photosynthesis and whole shoot growth at regular intervals throughout the six week experiment. The SD treated ramets showed drought symptoms at the leaf and whole plant levels of organization. Leaf level physiology in the CD treated ramets was indistinguishable from that of the watered ramets (CW, SW) only. CAM induction was not observed in any treatment. We conclude that water-sharing between ramets and not water saving via CAM induction is the primary mechanism of drought tolerance in this species.