RESPONSE OF WHEAT CULTIVARS TO DIFFERENT SOIL-NITROGEN AND MOISTURE REGIMES .3. LEAF WATER-CONTENT, CONDUCTANCE, AND PHOTOSYNTHESIS

Two greenhouse studies were conducted with contrasting patterns of soi l water availability and nitrogen (N) supply to extend our knowledge o f the combined effect of these environmental factors on cultivar respo nse of wheat (Triticum aestivum L.). Several parameters of water relat ions and photosynthesis were measured. Results showed that at the begi nning of stem elongation and before imposing water stress, the low N t reatment decreased leaf conductance and carbon dioxide (CO2) exchange rate (CER). This effect was more significant in the case of the cultiv ar Nesma than the other cultivars. Leaf conductance was a much better indicator of CER than chlorophyll content. Overall, water stress decre ased leaf conductance. Under mild stress, Nesma and Merchouch 8 behave d similarly, but Nesma was more sensitive to water stress. Increased N decreased CER under water stress but tended to have no effect on chlo rophyll concentration. Under well watered conditions, N application he lped the plants maintain greater leaf conductance, CER, and chlorophyl l concentration than low N supply. Cultivar and N effects on relative water content (RWC) were not significant. Under severe water stress, N esma tended to keep its stomata more open under N stress, while stomat a of Merchouch 8 were not sensitive to N level variation. High N decre ased leaf RWC of Nesma and Merchouch 8 but had no effect on Saada. Fro m this study we concluded that under non-water stressed conditions, ad ded N increased leaf water conductance, CER, and chlorophyll. Under wa ter stress, the cultivars responded differently to N application. High N decreased leaf conductance and relative water content. These result s indicated that careful cultivar selection can complement good N mana gement of wheat in areas prone to soil moisture stress.