Physiological, biochemical, and gene expression of Sour Orange (Citrus aurantium L.) to Iron(II)-Arginine Chelate under salinity, alkalinity, and salt–alkali combined stresses

•Fe (Arg) application increased proline and carbohydrate content by 16.40% and 13.21% and decreased the phenol and MDA content by 10.68% and 30.12%.•Enzyme activities such as peroxidase (POD), catalase (CAT), and super oxidase dismutase (SOD) were highest at pH 8.2 and salinity 120 mM and 0.2% Fe (Arg).•The highest expression of NAC36 and ERF109 genes were recorded at the co-treatments of pH 8.2, 60 mM NaCl and 0.2% Fe(Arg).•The highest photosynthesis rate, chlorophyll, and carotenoids, were obtained at pH 6.5, the salinity of 0 mM and 0.2% Fe (Arg) which increased by 3.70%, 22.44%, and 5.26%. In agricultural production systems, iron (II)-amino acid chelate is the latest novel compounds that enhance plant tolerance against soil stress. Salinity-alkaline stress can be considered one of the most critical threats to crops. This study was conducted to investigate the impact of iron(II)–amino acid chelate on some biochemical characteristics and genes expression of Sour Oranges under salinity and alkaline stress. The studied factors comprised two levels of pH (6.5 and 8.2), three levels of salinity (0, 60, and 120 mM NaCl), and three levels of Iron(II)–Arginine Chelate (0, 0.1, and 0.2%) in three replications. The results revealed that the highest photosynthesis rate was obtained at pH 6.5, the salinity of 0 mM and 0.2% Fe (Arg). Furthermore, Fe (Arg) application increased proline and carbohydrate content by 16.40% and 13.21% and decreased the phenol and MDA content by 10.68% and 30.12%, respectively, rather than the control. Enzyme activities such as peroxidase (POD), catalase (CAT), and super oxidase dismutase (SOD) were highest at pH 8.2, salinity 120 mM, and 0.2% Fe (Arg). Also, WRKY46 and MYB308 genes were highly expressed at pH 6.5, 120 mM NaCl and 0% Fe (Arg) and pH 8.2, 120 mM NaCl and 0.1% Fe(Arg) respectively. Moreover, the highest expression of NAC36 and ERF109 genes were recorded at the co-treatments of pH 8.2, 60 mM NaCl and 0.2% Fe(Arg), and pH 8.2 with no salinity stress and Fe(Arg) application, respectively. Therefore, Fe(Arg) foliar application partially alleviates the adverse effects of salinity and alkaline stress in Sour Orange.