Application of arbuscular mycorrhizal fungi and potassium nitrate improves physiological performance and glycyrrhizin production of licorice under salt stress

To examine the effects of potassium nitrate fertilizer (40 and 80 kg ha^-1) and inoculation with arbuscular mycorrhizal fungi (25, 50, and 100 g inoculum) on the physiological performance and glycyrrhizin production of licorice plants (Glycyrrhiza glabra L.) under salt stress (irrigation with 4 and 8 dSm^-1 of saline water), two field experiments were conducted in 2021 and 2022. Salinity reduced the physiological performance of plants but increased the concentration of glycyrrhizin in the roots. The application of potassium nitrate, especially at a rate of 40 kg ha^-1, along with mycorrhiza, resulted in increased nutrient content, antioxidative activities (catalase, peroxidase, and superoxide dismutase activities), membrane stability index, leaf relative water content, photosynthetic pigment content, glycyrrhizin production, and growth (about 45%) of licorice plants. On the other hand, the treatment with KNO₃ and mycorrhiza reduced the accumulation of sodium in plant tissues (about 16%). The application of 40 kg ha^-1 KNO₃ with 50 g of inoculum was found to be the superior treatment for improving the performance of licorice plants under salt stress. According to the findings of this study, the use of KNO₃ in combination with arbuscular mycorrhizal fungi is a successful approach to improve plant growth and productivity under saline conditions.