Growth, leaf gas exchange and physiological parameters of two Glycyrrhiza glabra L. populations subjected to salt stress condition

Salinity is the major environmental stress affecting growth and physiological processes in plants. Glycyrrhiza glabra (licorice) is a perennial medicinal plant having many secondary metabolites. The effects of 0, 100, 200, 400, 600, and 800 mM NaCl on growth parameters, leaf relative water content, chlorophyll index, gas exchange parameters, membrane stability index, antioxidant activity, phenolic compounds, flavonoid, and soluble carbohydrate contents of licorice populations (Fars and Khorasan) cultivated with different rhizomes diameters were evaluated. The soil and rhizomes elements were also studied. The results indicated that the salinity significantly decreased the growth parameters, relative water content, and membrane stability index, compared to the controls. The thicker rhizomes can grow more than thinner ones in saline soil. Chlorophyll index and leaf gas exchange were declined under salt stress. Besides, the soluble carbohydrate content was decreased. Salinity caused oxidative stress in licorice rhizomes, so that by decreasing the membrane stability index, antioxidant capacity, phenolic compounds, and flavonoid contents of rhizomes have increased in line with NaCl treatments. Na+, Cl-, and Ca2+ levels increased, but K+ concentration was reduced. The PCA-biplot analysis revealed that Fars and Khorasan populations had different responses to salinity. The length of rhizomes, flavonoids, phenolic compounds, and soluble carbohydrates of two licorice populations and salinity stress had the largest amount of difference of traits. Thus, the elevation of osmolytes, the nutrient balance, and the antioxidant capacity lead to protect of licorice under osmotic, ionic, and oxidative stress, which is caused by the salinity stress. Accordingly, G. glabra can withstand salinity up to 600 mM NaCl and be introduced as a halophyte plant.