Effect of Salt Stress on Growth, Water Relations, Solute Composition and Photosynthetic Capacity of the Xero-Halophyte Nitraria retusa (L.)

摘要

Nitraria retusa is common fodder shrub. The increasing interest in the utilisation of such shrubs in saline medium of North Africa requires evaluating the salinity effects on growth, water and solutes relationship, photosynthesis parameters in order to investigate salt-resistance mechanisms. Plants were grown in 0-800 mM NaCl under controlled conditions and harvested in three periods (after 60, 120 and 240 days). During the first harvest, the growth of N. retusa was promoted up to 400 mM NaCl, only to 200 mM NaCl in the two last harvests. Salt stress caused a marked decrease in osmotic potential, a significant accumulation of Na+ and Clˉ and a concomitant decrease in K+ and Ca2+ contents while magnesium, nitrogen and phosphorus contents were not greatly affected. Plants are able to maintain a higher leaf water content which was probably associated with a greater capacity for osmotic adjustment. The organic osmotica that can be involved in osmotic adjustment was proline, soluble sugar and at least degree glycinebetaine. Moderate salinity had a stimulating effect on growth rate, net CO2 assimilation (Pn), transpiration (E) and stomatal conductance (gs). At higher salinities levels, these physiological parameters decreased significantly. There was no significant changes on the chlorophyll fluorescence for N. retusa stressed plants. Carotenoid content was highest at 800 mM. For the chlorophyll content, it was unaffected up to 400 mM and then decreased slightly at 800 mM. Mesophyll of N. retusa leaves were thinner in salt-stressed plants while epidermis thickness was unaffected by salinity and the stomatal density decreased significantly with higher salt treatments. The results suggest that N. retusa show high tolerance to high salinity. The tolerance to salinity appears to be achieved through two mechanisms compartimentation of ions at moderate salinity and salt excretion at very higher salinity.