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Abstract
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Salinity has a global impact on plants by inducing biochemical and metabolic changes that lead to oxidative stress, impairing growth, yield, and productivity. The pistachio tree (Pistacia vera L.) is a salt-tolerant species. This study aims to investigate the effectiveness of carbon nitride nanostructures modified with iron (Fe/C₃N₄) on the Akbari pistachio variety under salinity stress levels (0, 50, 100, and 150 mM) and foliar applying (distilled water as a control, Fe₂O₃ (0.2 g L–1), C₃N₄ (0.2 g L–1), and carbon nitride modified with iron or Fe/C₃N₄ (0.2 g L–1). The findings showed that salinity decreased relative water content (RWC), SPAD index, membrane stability index (MSI), maximum fluorescence (Fm), and variable fluorescence (Fv), and increased hydrogen peroxide (H2O2). However, foliar application with Fe₂O₃, or Fe/C₃N₄, improved all traits. Nevertheless, there was no significant interaction between the applied mitigating treatments and salinity levels on RWC, MSI, SPAD index, Fm, Fv, and H₂O₂. Salinity stress increased malondialdehyde (MDA), phenol, and flavonoid levels, and reduced leaf number, height, photosynthetic pigments, vitamin C, and total protein. The application of foliar treatments, especially Fe/C₃N₄, improved the influence of salinity stress. Additionally, the activity of antioxidant enzymes increased under salt stress and foliar application. Fe/C₃N₄-treated seedlings consistently exhibited higher growth and photosynthetic traits and lower oxidative damage than untreated controls across salinity levels, indicating a stable physiological benefit rather than a salinity-specific effect.
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