Effect of NaCl on Photosynthesis of Two Wheat Species (Triticum durum and T. aestivum) Differing in their Sensitivity to Salt Stress

Two wheat species, Triticum aestivum, cv. Tanit and T. durum, cv. Ben Bachir, were cultivated hydroponically and subjected to salt stress (50 or 100 mmol/L NaCl) up to 21 days. NaCl treatment resulted in growth reduction for both varieties (but less for Ben Bachir than for Tanit), equivalent Na+ and Cl− absorption by the whole plants, and the capacity for Ben Bachir to transport ions into the leaves where they accumulated. This accumulation process accounts for the maintainance of the water status in Ben Bachir leaves. As a whole, Ben Bachir shows characteristics of a NaCl-tolerant species. Net CO2 uptake by the non-tolerant Tanit variety was markedly reduced at PPFD higher than 500 µmol m−2 s−1, mostly because of stomatal closure, as shown by the decrease in the Ci/Ca ratio, the effect of saturating CO2 concentrations (5 %) and the increase in the δ13C in the salt-treated leaf tissues. No effect of salt stress could be found either on the initial slopes of the net CO2 assimilation curve, on the Fv/Fm ratio of chlorophyll fluorescence, or on the carboxylative capacities in the leaves. As a whole, these results favour the hypothesis of an exclusive effect of salt stress on the stomatal behaviour of the treated leaves.