Decreasing the Na+/Ca2+ Ratio Improves the Performance of Pistacia species Grown in Saline Soils

A reduction in the sodicity has been found to improve crop plants grown in saline conditions, but little is known about the effect of the same on pistachio trees. Therefore, an experiment was conducted to determine the physiological responses of two rootstocks, a UCBI seedling (P.atlantica x P.integerrima ) and a PGII clone (P.integerrima x P.atlantica), both budded with the female Kerman scion, (P.vera cv. Kerman) to two salinity levels with three Na+/Ca2+ ratios. The six salinity treatments and one control were replicated five times. The six treatments were a mixture of NaCl and CaCl2 formulated to produce two levels of salinity (4.5 and 9.5 dS/m) and three different Na+/Ca 2+ ratios (2, 20, and 50 on a molar basis) within each salinity treatment. During the 60-day treatment period, the predawn SWP and relative growth rate were measured. At the end of the experiment, all the plants were harvested, and Na+, K+, Mg2+, Ca +2, and Cl- concentrations in the leaves, and Na+ concentration in roots, rootstock trunk, and scion trunk were measured. Based on the relative growth rate, Kerman on PGII was more tolerant to salinity compared to Kerman on UCBI. Kerman on PGII accumulated more Na+ in its fine roots compared to Kerman on UCBI, but it transferred less Na+ to its mature leaves. In most cases, decreasing the Na+/Ca2+ ratio at a given salinity increased the relative growth rate. These results suggest that at salinity levels of 4.5 and 9.5 dS/m, reducing the Na+/Ca2+ ratio to 2 improved the relative growth rate of both rootstock-scion combinations compared to their response at equal salinities when the Na+/Ca 2+ ratio was 50. However, the trend of data showed that Kerman scion on a PGII rootstock had higher growth in 9.5 dS/m salinity level than the same scion on a UCBI rootstock. For all plants at each Na+/Ca 2+ ratio (2, 20, and 50), increasing the salinity level did not significantly increase the Na+ and Ca2+ concentrations in the mature leaves. At each Na+/Ca2+ ratio, increasing salinity did not affect mature leaf K+ and Mg2+ concentrations in Kerman on PGII rootstocks. Increasing salinity decreased the Mg2+ concentrations in mature leaves of Kerman on UCBI but did not change mature leaf K+ concentration.