Salt tolerance of two wheat genotypes in response to the form of nitrogen

Two wheat genotypes (Triticum aestivum L. cv. Giza 157 and cv. Sakha 8) were grown hydroponically under greenhouse conditions. Plants were subjected to different levels of salinity: 0, 75 and 150 mM NaCl in nutrient solutions containing either NH4+, or NO3- as the sole nitrogen source at a concentration of 12 mM. Growth of the two cultivars, particularly Sakha 8, was better under nitrate than under ammonium nutrition. Ammonium-fed plants were poorly developed with a distinctly lower root: shoot ratio and thick, short and highly branched roots compared with nitrate-fed plants. The two cultivars exhibited greater salt (NaCl) tolerance under nitrate than under ammonium nutrition. Both ammonium nutrition and salinity reduced the uptake of K+ and Ca2+, but increased the uptake of Na+ by both cultivars; this led to lower K+/Na+ ratios relative to either nitrate-fed, or non-saline plants. In addition, ammonium nutrition reduced the proportions of plant K+, Na+ and Ca2+ retained by the root. The toxic effect of ammonium nutrition on wheat can thus be related to retarded uptake of K+ and Ca2+ and to enhanced uptake of Na+. The results suggest that nitrate, rather than ammonium, is favored as a nitrogen source for cultivars Giza 157 and Sakha 8 of wheat, particularly under salt stress.