The effects of salinity and heat stress on some physiological and vegetative characteristics of peppermint (Mentha piperita L.) at different time intervals

This study investigated the effects of simultaneous salinity and heat stress on some physiological and vegetative characteristics in peppermint. The effect of three levels of salinity (0, 60 and 120 mM of sodium chloride) and two levels of thermal stresses (25°C and 35°C) at 24, 48 and 72 hours after treatments were measured on some physiological and morphological characteristics of Mentha piperita L. in a completely randomized design with three replications. The results showed that simultaneous salinity and heat stress increased the relative levels of phenolic and proline compounds. At 35 ° C and 120 mM salinity, the amount of proline increased by 2.32, 2.5 and 1.92 times compared to the control at 24, 48 and 72 hours, respectively. The highest accumulation of phenolic compounds was observed at 35 ° C and salinity of 120 mM after 72 hours equal to 3.3 mg/g. The content of soluble sugar, carotenoids, total chlorophyll and calcium in peppermint seedlings had a decreasing trend. At 120 mM salinity, the ratio of K+/Na+ compared to the control decreased by 8.44, 10.37 and 9.35 times in 24, 48 and 72 hours, respectively. Salinity and heat stress decreased the fresh and dry weight of shoots, but in contrast, the fresh weight and dry weight of roots showed a significant increase. Simultaneous salinity and heat stresses are limiting factors for the cultivation of peppermint. The simultaneous stress of salinity and heat increased the amount of phenol, which could improve the quality of peppermint..