A Study on the Optimal ABA Concentration for Enhancing Cold Resistance in Astragalus Based on a Comprehensive Evaluation of Multiple Physiological Indices

This study investigates the effects of exogenous abscisic acid in improving cold resistance in two medicinal Astragalus species, A. membranaceus and A. mongholicus, respectively. ABA was applied via foliar spraying at six concentrations (0, 5, 10, 15, 20, and 30 mg/L), after which plants were subjected to 4°C for 72 h. A series of physiological parameters were measured, including relative electrolyte leakage, MDA content, osmotic regulators (soluble sugars, soluble proteins, proline), antioxidant enzyme activities (superoxide dismutase, peroxidase and catalase), and total chlorophyll content. The results indicate that 15 mg/L ABA most effectively alleviated membrane damage and oxidative stress, while also enhancing osmotic adjustment and antioxidant enzyme activities. Both principal component analysis and membership function evaluation consistently identified 15 mg/L as the optimal ABA concentration, with significantly higher comprehensive scores and average membership values compared to other treatments. Interspecific differences were observed between the two species. A. membranaceus exhibited a stronger response in membrane protection and antioxidant enzyme activation, whereas A. mongholicus relied more on osmotic regulation for cold tolerance. These findings demonstrate that 15 mg/L ABA significantly enhances cold resistance in both species and provides a practical and effective strategy for mitigating cold stress in Astragalus cultivation.