<p>Alkaline stress is considered as one of the major abiotic stress factors limiting plant production on a global scale. This study was conducted in vitro to evaluate the physiological, morphological, and biochemical responses of Garnem rootstock to NaHCO₃-induced alkaline stress using sodium nitroprusside (SNP) and salicylic acid (SA) treatments. The aim was to alleviate the negative effects of alkaline stress. The study was conducted during the rooting stage of Garnem rootstock plantlets obtained through in vitro micropropagation. SNP and SA (50, 100, and 150 µM) were applied in vitro to counteract alkaline stress induced by NaHCO₃ (0 mM, 20 mM, and 40 mM) at various concentrations. As the severity of alkaline stress increased, damage occurred to morphological, physiological, and biochemical parameters. The SNP and SA treatments alleviated the harmful effects of alkaline stress. In the study, the highest survival rate was observed with 0 mM NaHCO₃ + 50 µM SA (98.33%) and 50 µM SNP (95.00%), while the lowest survival rate was observed with 40 mM NaHCO₃ + 150 µM SA (6.67%). The longest shoots were observed with 0 mM NaHCO₃ + 100 µM SNP (4.25&#xa0;cm), and the shortest shoots were observed with 40 mM NaHCO₃ + 150 µM SA (0.77&#xa0;cm). The highest number of leaves was found with 20 mM NaHCO₃ + 50 µM SA (20.63 per plantlet), and the lowest number of leaves was found with 20 mM NaHCO₃ + 150 µM SNP (5.33 per plantlet). The highest plant fresh weight was observed with the 0 mM NaHCO₃ + 50 µM SNP (2.07&#xa0;g), while the lowest plant fresh weight was observed with the 20 mM NaHCO₃ + 150 µM SA (0.14&#xa0;g) application. The highest plant dry weight was observed with the 0 mM NaHCO₃ + 150 µM SA (0.24&#xa0;g), while the lowest plant dry weight was observed with the 20 mM NaHCO₃ + 150 µM SA and 40 mM NaHCO₃ + 150 µM SA (0.04&#xa0;g) applications. The highest injury was observed with 40 mM NaHCO₃+ 50 µM SA, 40 mM NaHCO₃+ 100 µM SA and 40 mM NaHCO₃+ 150 µM SA (4.00) and the lowest injury was observed with 0 mM NaHCO₃+50 µM SNP, 0 mM NaHCO₃+100 µM SNP and 0 mM NaHCO₃+150 µM SNP (1.00). Membrane permeability increased under high alkaline stress, while 100 µM SNP applications reduced this rate, contributing to the preservation of cellular structure. All SNP and 50 µM SA applications increased leaf relative water content in response to alkaline stress. Significant decreases in chlorophyll a, chlorophyll b, and total chlorophyll concentrations were observed under alkaline stress conditions. However, SNP treatments alleviated these negative effects and increased chlorophyll levels. Furthermore, SNP treatments significantly reduced hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) accumulations. Overall, the results demonstrated that SNP treatments at all tested concentrations effectively mitigated NaHCO₃-induced alkaline stress by improving morphological traits, maintaining membrane integrity, enhancing leaf relative water content and reducing oxidative damage in Garnem rootstock plantlets. In contrast, salicylic acid exhibited a concentration-dependent response, with low doses (50–100 µM) alleviating stress effects, whereas the high concentration (150 µM) induced phytotoxicity and markedly suppressed plant growth and physiological performance.</p>