Abstract
Leafless
Duvalia velutina
Lavranos (Apocynaceae) is an arido-active stem succulent common in the arid region southwest of the Arabian Peninsula. This region is characterized by a short wet season with erratic rainfall and a long dry season with high temperature and high irradiance. We investigated the survival strategy of
D. velutina
by studying nurse association, gas exchange, and chlorophyll fluorescence. Results showed that
D. velutina
exhibited the strict nurse association with shade for protection against heat and high irradiance. Results also showed that
D. velutina
is an obligate CAM plant with ample physiotypic plasticity involving a shift to CAM-idling under prolonged drought. Chlorophyll fluorescence measurements revealed water stress-induced reduction of PSII activity occurring in concomitance with a marked rise of nonphotochemical quenching and chlorenchyma anthocyanin content. These results reflected photoprotective capacity involving nonradiative excess energy dissipation and antioxidative attributes. We concluded that the complex survival strategy of
D. velutina
in its natural arid habitat includes a multifaceted interplay of nurse association, physiotypic plasticity, and photoprotective mechanisms.