Photosynthetic response of Populus euphratica to salt stress

P. euphratica Olive and the hybrids (P. talassica, Kom X (P. euphratica + Salix alba L.)) seedlings were subjected to low (50 mM NaCl) and high salt (200 mM NaCl) treatments to determine their photosynthetic responses to salt stress. The photosynthetic pattern indicated that P, euphratica is a C3 plant with a high CO₂ compensation point (150 μmol mol^-1) and saturation point (900 μmol mol^-1), but has some characteristics of C4 plants with a high light saturation points (2800 μmol m^-2 s^-1) in control conditions, CO² compensation and saturation points increased with high salt treatment for both the hybrid and P. euphratica while light saturation point decreased with salt treatment. The net photosynthesis of P. euphratica with high salt treatment declined in the first 14 days and recovered to 70%, that with control in day 21 when soil salt content was about 0.7% NaCl, while that of the hybrids did not recover when soil salt content was about 0.5% NaCl with high salt treatment. With increasing salt levels, Chlorophyll a contents and Chlorophyll a/b ratio increased, while Chlorophyll b and carotenoid contents decreased by day 10, when photosynthesis was heavily depressed for both species. Fluorescence patterns confirmed that reduction of photosynthesis under high salt treatment was not due to damage of the photosynthetic apparatus, but more likely due to inhibition of the dark reaction.