Exogenous Application of Phytohormones Alleviates Salt Injury to Growth, Physiological, and Biochemical Attributes of Hemp Seedlings

Hemp (Cannabis sativa L.) is an environmentally friendly crop with a rich history and promising market prospects. To avoid competing with staple crops for land, we propose that utilizing salt-affected soil could be a potential strategy for developing the hemp industry. However, hemp plants are glycophytes, which means that their salt tolerance needs to be improved. Phytohormones are known to play critical roles in regulating plant responses to stress. Thus, in this study, the effects of foliar spraying of abscisic acid (ABA), salicylic acid (SA), gibberellin A3 (GA(3)) and alpha-naphthalene acetic acid (NAA) on the salt tolerance of hemp seedlings were evaluated. The seedlings were treated with 200-mmol/L NaCl and different concentrations of ABA, SA, GA(3), or NAA through sand culture experiments. The results showed that the growth of salt-treated hemp seedlings (in terms of plant height, stem diameter, and biomass) was significantly improved by spraying 250-mg/L ABA, 250-mg/L SA, 150-mg/L GA(3), or 100-mg/L NAA. Spaying the hemp salt-treated seedlings with these phytohormone concentrations decreased the malondialdehyde content, Na+/K+ ratio, and electrolyte leakage but increased the endogenous indole-3-acetic acid, chlorophyll, carotenoid, soluble sugar, and soluble protein contents, K+ concentration, superoxide dismutase activity, and peroxidase activity. This study is the first to show the effectiveness of ABA, SA, GA(3), and NAA in alleviating the adverse effects of salt on hemp seedlings. These novel findings suggest that the exogenous application of phytohormones may serve as a potential management tool to improve the salt tolerance of hemp plants.