Synergistic alleviation of salinity stress in tomato: unraveling the physiological, biochemical, and antioxidant mechanisms modulated by manganese nanoparticles and chitosan

), applied separately and in combination. Salinity significantly decreased biomass and photosynthetic pigments while increasing lipid peroxidation and oxidative stress. Under severe salinity (80 mM NaCl), the combined treatment substantially enhanced plant performance, doubling shoot fresh weight and increasing root fresh weight by 55.5% compared to stressed controls. Chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids increased by 25.8%, 29.4%, 35.8%, and 91.1%, respectively. Oxidative damage markers, including malondialdehyde and aldehydes, were markedly reduced. Antioxidant responses were significantly elevated, with guaiacol peroxidase and polyphenol oxidase activities increasing by up to 300% and 104%, respectively. Additionally, phenolics, flavonoids, DPPH activity, and soluble proteins improved. These findings demonstrate a synergistic nano-biopolymer effect that enhances physiological resilience and stress tolerance, offering a promising strategy for sustainable tomato production in saline environments.