Interactive Effects of Salinity and Ozone Pollution on Photosynthesis,Stomatal Conductance,Growth, and Assimilate Partitioning of Wheat (Triticum aestivum L.)

Plants of an Egyptian cultivar of wheat (Triticum aestivum L. cv. Giza 63) were exposed in open-top chambers (OTCs) for 8 h d^–1 for up to 75 d to a factorial combination of two levels of salinity (0 and 50 mM NaCl) and two levels of O₃ (filtered air and 50 mm³ m^–3). Exposure to 50 mm³ m^–3 O₃ significantly decreased stomatal conductance (g _s), net photosynthetic rate (P _N), and chlorophyll (Chl) content by 20, 25, and 21 %, respectively. This reduction resulted in a change in assimilate allocation in favour of shoot growth leading to a decrease in root to shoot ratio and eventually to a decrease in relative growth rate (RGR) of both root and shoot. There was a very large reduction in yield parameters, especially in the number of ears/plant and 1 000-grain mass. Soil salinity significantly reduced P _N and g _s by 17 and 15 %, respectively, while Chl content was increased by 17 %. Root growth was decreased leading to an increase in root/shoot ratio. Yield parameters were decreased due to salt stress. There was antagonistic interaction between salinity (50 mM NaCl) and O₃ (50 mm³ m^–3) showing that salinity effectively protects against the adverse effects of O₃ by increasing g _s during O₃ fumigation.