Ecophysiological studies on three desert plants growing in Wadi Natash, Eastern Desert, Egypt.

Abstract

Physiological adjustments to enhance tolerance or avoidance of drought were studied in three desert plants growing in Wadi Natash (Eastern Desert, Egypt). Studied plants (Zilla spinosa (L.) Prantl, Citrullus colocynthis (L.) Schrad and Morettia philaeana (Dalile) DC.) were collected from four stands. Cell sap osmotic potential, some organic (soluble sugars, total free amino acids, and soluble proteins) and inorganic (Ca2+, Mg2+, Na+, K+, Cl- and SO42-) solute  concentration were determined. In addition, cover degree of investigated species (according to the cover-abundance scale of Braun-Blanquet) was also estimated. Substantial osmotic adjustment (up to -1.71 MPa) was observed in Z. spinosa collected from stand 4. Z. spinosa was dependent on soluble sugars, soluble proteins, free amino acids, SO42-, K+, Cl- and Mg2+ to readjust their internal osmotic pressure and to improve its water status. It preferred Mg2+ more than the two other species. C. colocynthis accumulated inorganic solutes more than Z. spinosa and less free amino acids. The results suggest that osmotic adjustment was the main water relationship adaptation to cope with drought. Accumulation of soluble sugars, soluble proteins, K+, Cl- and SO42- at higher concentration often assist in turgor maintenance and helped to enhance drought tolerance.