Pistachio is an important and high-value nut crop with a growing cultivation in Iran. Therefore, applying appropriate approaches to increase the quality and quantity of pistachio yeild is necessary. In a one-year field experiment, the effects of foliar application of zinc (Zn) in the form of mineral (ZnSO 4 ) and complexed with lysine (Zn-Lys) and lysine plus methionine (Zn-Lys-Met) in the presence and absence of ascorbic acid (Asc) on yield and quality attributes of pistachio ( Pistachio vera L. cv. Akbari) were evaluated. Lys and Asc alone treatments were used to distinguish the effects of accompanying Lys and Asc. A control treatment with no amino acids and Zn was also used. Foliar spray treatments were applied at 15 Ordibehesht and 30 Khordad, twice with 2 d intervals. Results showed that foliar application of Zn, regardless of applied source, significantly increased leaf Zn concentration in comparison with control. Higher total yield, fresh and dry mass of shelled and unshelled 100-nut, dry mass of kernels and percentage of non-split shells were measured for the pistachio trees supplemented with Zn in comparison with the controle. Foliar application of Zn resulted in significant decrease of empty nuts and abscission of inflorescence buds. The effectiveness of Zn-Lys in improving yield and quality attributes of pistachio was higher than other Zn sources. The presence of amino acids resulted in lower contribution of symplastic uptake of Zn in comparison with apoplastic retention. Also, total leaf and kernel Zn concentrations were lower at the Zn-Lys treatment than the Zn-sulfate treatment. It seems that the accompanying amino acids were effective in increasing translocation of Zn from the leaves to kernels. The critical deficiency concentration of Zn in the leaf and fruit to achieve the highest nut yield and lowest abscission of inflorescence buds were 37.6 and 46.2 mg/kg, respectively. The effect of fertilizer solution pH on Zn uptake by pistachio leaves was also investigated. Based on the results, regardless of Zn fertilizer source (Zn-Lys and Zn-sulfate), Zn uptake by leaves decreased by increasing solution pH. The highest and lowest Zn uptake was obtained at pH=3.5 and pH=8, respectively. Keywords: Amino acid, Apoplastic retention, Fertilizer solution pH, Pistachio, Zinc, Symplastic uptake
