Influence of high levels of Na+ and Cl-on ion concentration, growth and photosynthetic performance of three salt-tolerant plants

This study aimed to measure the effects of elevated levels of Na+ and Cl− on ion concentration, growth, and photosynthetic performance of Melilotus siculus, Tecticornia pergranulata, and Thinopyrum ponticum in pot trials under controlled glasshouse conditions. Experiments were conducted using Na+ and Cl− dominant saline soil treated with constituted saline solutions (0, 2.0 and 4.0 dS m−1 Na+ or Cl−). Maximum Na+ and Cl− concentration was in T. pergranulata shoots; maximum Na+ concentration was in T. pergranulata roots, whereas maximum Cl− in T. ponticum roots. Maximum quantum yield of PSII [Fv/Fm] values did not change significantly. Net-photosynthetic rate [Pn] and stomatal conductance [gs] values increased and non-photochemical quenching [NPQ] value decreased significantly in T. pergranulata with increasing Na+ dominant treatments and the reverse occurred in Cl− dominant treatments. Pn, gs, and NPQ values did not significantly change in T. ponticum with increasing Na+ and Cl− dominant treatments. The shoot and root biomasses of T. pergranulata were the maximum at 4.0 dS m−1 Na+ dominant treatment. In T. ponticum, the maximum shoot and root fresh masses and shoot dry mass occurred in the control treatment and the maximum root dry mass occurred in the 2.0 dS m−1 Cl− dominant treatment. In T. pergranulata, strong positive correlations occurred between Na+ concentration in shoots and salt tolerance (shoot mass over control) and moderately positive correlation occurred between Cl− concentration in shoots and salt tolerance. However, strong negative correlations were observed between Na+ and Cl− concentration in shoots and salt tolerance in T. ponticum as well as between Cl− concentration in shoots and salt tolerance in M. siculus. Our glasshouse experiments indicate that 4.0 dS m−1 Cl− solutions in the soil was more intensely damaging than that of Na+. The greatest concentration of both Na+ and Cl− was in T. pergranulata under the tested circumstances indicating it to be the candidate of choice for restoring saline soils, followed in capacity by M. siculus and T. ponticum.