Effects of foliar treatment of ascorbic acid on industrial hemp seedlings under drought stress

Industrial hemp (Cannabis sativa L.) seedlings are sensitive to drought stress, which is a prevalent factor influencing its growth seriously. To explore the effect of ascorbic acid (AsA) on hemp seedlings under drought condition, a pot experiment was carried out to applicate AsA on two cultivars, ‘Yunma1’ (YM) and ‘Bamahuoma’ (BM). Three drought treatments were imposed: control (normal water), drought (50% substrate moisture) and drought + AsA (50% substrate moisture + 200 mg/L AsA). The results showed that drought stress significantly suppressed plant height and reduced plant fresh weight, with reductions of 59% and 75% observed in YM, and 43% and 67% in BM, respectively. Although foliar treatment with AsA had little effect on increasing plant fresh weight under drought conditions, it significantly enhanced the concentrations of photosynthetic pigments and the activities of antioxidant enzyme (superoxide dismutase, SOD and peroxidase, POD). The results suggested that harmful effects of drought stress on hemp seedlings were mitigated by exogenous application of AsA, which decrease the breakdown of photosynthetic pigments, enhancing antioxidant enzyme activities and strengthening the antioxidative defense system. Among these, compared to drought treatment the carotene content and SOD activity exhibited the most significant increases after AsA spraying. Specifically, exogenous AsA treatment increased the carotene content by approximately 108.40% in YM and 88.53% in BM. Meanwhile, POD activity increased by 33.33% in YM and 60.94% in BM. Furthermore, the study found that hemp plant response and tolerance to drought were cultivar-dependent. Overall, these results provide a theoretical basis for understanding the mechanism by which AsA alleviates drought stress.