Physiological Effects of Bacillus subtilis on Licorice Seedlings under Drought Stress Induced by Polyethylene Glycol 6000

This study examines the physiological effects of Bacillus subtilis (B. subtilis) on licorice (Glycyrrhiza uralensis Fisch.) seedlings under drought stress, aiming to establish a scientific foundation for enhancing drought resistance and yield in licorice. The experiment comprised four treatment groups: control group (CK), drought group (D), drought + B. subtilis group (D + J), and control (Hoagland nutrient solution) + B. subtilis group (CK + J). Drought conditions were simulated using polyethylene glycol 6000. The study analyzed biomass, soluble sugar, starch, antioxidant enzyme activities, and photosynthetic parameters of licorice seedlings to evaluate the effects of B. subtilis. The results indicated that drought conditions inhibited licorice growth and photosynthesis, promoted starch accumulation, decreased root peroxidase (POD) and superoxide dismutase (SOD) activities, and enhanced leaf catalase (CAT) and SOD activities. Under drought stress, the application of B. subtilis significantly enhanced plant height, root-to-shoot ratio, and root fresh weight of licorice seedlings, elevated leaf CAT activity, and improved photosynthetic parameters, including net photosynthetic rate, stomatal conductance, maximum photochemical rate, actual quantum efficiency of photosystem II, electron transport rate, photochemical quenching coefficient, and non-radiative quenching coefficient. Thus, B. subtilis enhances drought resistance in licorice seedlings by regulating stomatal function, optimizing antioxidant defense systems, and improving light energy utilization efficiency.