Seasonal changes in physio-biochemical responses of the xerophytic dwarf shrub Haloxylon salicornicum in the Kuwait desert

The combination of high temperatures and drought is one of the main environmental characteristics of desert ecosystems in arid regions. In the hyperarid desert of Kuwait, the xerophytic dwarf shrub Haloxylon salicornicum (Moq.) Bunge ex Boiss. regularly maintains its vegetative growth for prolonged periods of severe hot and dry conditions in summer. The present study was conducted to explore cellular-level mechanisms of plant tolerance to a combination of high temperatures and drought stress in summer compared to the responses of the same individual plants under moderate environmental conditions in spring. The physio-biochemical changes measured in the stem tissues involved those that enhanced osmotic adjustment and enzymatic antioxidant systems, both of which maintain photosynthetic pigment biosynthesis. The relative water content was significantly reduced in summer by 17 %, although plants stored a considerably higher amount of water in their slightly succulent branch tissues. Plants preferentially accumulated soluble sugars in substantial amounts (27 %), whereas proline content was significantly reduced by 28 %. The potential role of inorganic ions and carotenoids in enhancing the plant's abiotic stress tolerance is also addressed. Our study suggests that H. salicornicum can serve as an excellent model for understanding the adaptative mechanisms of xerophytes in hot and dry deserts.