Ecophysiological studies of three desert plants growing in two different habitats, central region, saudi arabia

Physiological adjustment to enhance tolerance or avoidance of drought were studied in three desert plants growing in Al-Thomamah and Al-Derayah habitats, central region, Saudi Arabia. Studied plants Tamarix aphylla L., Zygophyllum coccineum L. and Artemisia monosperma Del. were collected from three stands for each habitat in March 2012. Cell sap osmotic potential, some organic (soluble sugars, total lipids content, soluble proteins, and free fatty and amino acids) and inorganic (K+, Na+, Ca2+, Mg2+, Cl-, SO42- and HCO3-) soluble concentration were determined. In addition, chlorophyll a, b, and total nitrogen content and physiochemical parameters of the soil samples support the studied three plants were also determined. Substantial osmotic adjustment (up to 2.6 MPa) was observed in Z. coccineum collected from Al-Thomamah habitat. Tamarix aphylla was dependent on soluble sugars, soluble proteins, and free amino acids, Ca2+, Mg2+, Cl- and SO42- to readjust their internal osmotic pressure and to improve its water status. It preferred Mg2+ concentration more than the two other plant species. Zygophyllum coccineum accumulated inorganic more than Tamarix aphylla and less free amino acids. The results suggest that, the osmotic adjustment was the main water relationship adaptation to cope with drought. Accumulation of soluble sugars, soluble proteins, free fatty and amino acids (especially proline) and inorganic elements at higher concentration often assist in turgor maintenance and helped to enhance drought tolerance.