Cadmium and zinc in saline soil solutions and their concentrations in wheat

Soil salinity and plant genotype may affect bioavailability of Cd and Zn to wheat. The aim of this study was to investigate the relationship between concentrations of Zn and Cd in saline soil solutions and in different wheat genotypes. A greenhouse experiment with four bread wheat genotypes (Triticum aestivum L. cv. Rushan, Kavir, Cross, and Falat), and a durum wheat (Triticum durum L. cv. Durum), at four salinity levels of irrigation water (0, 60, 120, and 180 mM NaCl) in triplicate was conducted. After 45 d of growth, the shoots were harvested, and Zn and Cd concentrations were determined in the shoots. Speciation of Cd and Zn in saturation paste extract was modeled using MINTEQA2. A significant (P < 0.05) correlation was observed between model results and Cd and Zn species measured using Amberlite resin. Cadmium and Zn speciation in MINTEQA2-calculated soil solution was affected by salinity but not by wheat genotype. The major Cd species present in MINTEQA2-calculated soil solution were free Cd(2+), CdCl(+), and CdSO4(0), that increased with increasing salinity. Free Zn(2+) was the dominant Zn-species for all salinities and decreased with increasing salinity. Increasing salinity resulted in significant increases and decreases in shoot Cd and Zn concentrations, respectively, of the Zn-inefficient genotypes. Cadmium concentrations in shoots of Durum and Kavir genotypes were best predicted by CdCl(+) concentrations in solution. In contrast, free Zn(2+) ion concentrations in MINTEQA2 calculated soil solution were best related to shoot Zn concentrations in Zn-efficient genotypes. Under saline conditions, Zn and Cd speciation effects on bioavailability thus depend on both plant genotype and the metal of interest.