Effects of exogenous chitosan concentrations on photosynthesis and functional physiological traits of hibiscus under salt stress.

Background: Soil salinity is a major barrier to plant growth and yield improvement. Chitosan, a versatile biomaterial, has shown potential in enhancing plant stress tolerance. This study evaluated the effectiveness of chitosan pretreatment in mitigating salt stress hibiscus (Hibiscus syriacus L.). Two-year-old hibiscus cuttings were treated with varying concentrations of chitosan (10 mg/L, 25 mg/L, 50 mg/L, 100 mg/L) via root irrigation and foliar spray in a 6‰ saline environment. Growth parameters, gas exchange rates, antioxidant enzyme activities, and osmotic regulatory compounds were analyzed.

Results: The results showed that chitosan at 25 mg/L and 50 mg/L significantly improved physiological and ecological traits. These concentrations enhanced photosynthetic performance, protected photosynthetic electron transport chain, and reduced malondialdehyde (MDA) content and relative conductivity, thereby limiting cell membrane damage. Additionally, the accumulation of soluble proteins, soluble sugars, and proline increased, improving the plants' ability to cope with salt stress. Antioxidant enzyme activities, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), were notably elevated, while levels of hydrogen peroxide (H₂O₂) and superoxide anion (O₂^-) decreased.

Conclusions: The 25 mg/L and 50 mg/L treatments had the most pronounced effects, confirming that moderate chitosan concentrations effectively alleviate salt stress in hibiscus. This study underscores the role of chitosan in enhancing salt stress adaptability, offering insights for plant protection and greening efforts.