Growth, chemical composition, and carbon isotope discrimination of pistachio (Pistacia vera L.) rootstock seedlings in response to salinity

Pistachio is considered a potential crop for many semi-arid regions affected by salinisation. We examined the effects of salinity on growth of 3 pistachio rootstocks: Badami-e-zarand, Sarakhs, and Ghazvini. Rootstocks were grown in soil in 8-L polyethylene pots and irrigated every 3 days with treatments of 0, 75, 150, or 225 mM NaCl. We measured above-ground biomass, allocation of C to root systems and foliage, and carbon isotope discrimination (Delta) and proline accumulation after 30 days and again after 60 days. Relative growth rate (RGR) decreased with time for all treatments and rootstocks. RGR and net assimilation rates (NARw) decreased with increasing salinity. In all rootstocks, NARw, but not leaf weight ratio (LWR), was significantly correlated with RGR, indicating that NARw was an important factor underlying growth responses among rootstocks. Increased salinity did not affect leaf water potential (psi(leaf)), even though proline concentrations increased with increasing NaCl concentration, particularly in the Ghazvini rootstocks. Both Cl- and Na+ concentrations in leaves increased from 30 to 60 days but not in roots and stems. The Sarakhs rootstocks accumulated more of Cl- and Na+ compared with other rootstocks. K+ concentration in the roots and stems of all rootstocks also decreased with increasing salinity at both 30 and 60 days. Concentrations of Ca2+ in stems and root systems, but not in leaves, were also reduced by increased salinity in all rootstocks but only after 60 days. Carbon isotope discrimination (Delta) decreased with increased salinity in the leaves, stems, and roots; however, there was no significant difference in carbon isotope discrimination among rootstocks. We conclude that the Ghazvini rootstock was the most salt tolerant among the rootstocks tested. Carbon isotope discrimination in pistachio rootstocks may be a useful indicator of cumulative salinity history of the plant but is not a suitable indicator for pre-screening of pistachio rootstocks for salinity resistance.