Salt Stress Dynamics in Monarda citriodora Cerv.ex Lag; An Integrative Analysis of Growth, Biochemical responses and essential oil modulations

Abstract Monarda citriodora , a highly valued plant with essential oil and medicinal properties, is being exclusively cultivated at CSIR-IIIM Jammu, India. Salt stress poses significant challenges to plant growth, development, and productivity, impacting agricultural output worldwide. In this study, the impact of four salts NaCl, KCl, MgSO 4 and CaCl 2 at concentrations (0, 25, 50, 100, and 200 mM) on the growth, biomass, nutrient, relative water content, proline content, antioxidant activity, and essential oil constituents of M. citriodora . A completely randomized design was used in a pot experiment and plants were irrigated with different salinity levels for 60 days, followed by two months of transplanting. The results showed that higher salt concentrations decreased nutrients, growth, biomass, chlorophyll and relative water content. Proline concentration and antioxidant activity were enhanced with increasing salt concentrations. Thymol is the main constituent in essential oil (39.26–91.36%). The thymol content was elevated at 50 mM salt concentrations, with the highest content (91.36%) found in the 50 mM KCl treatment, followed by 50 mM NaCl (91.07%) and 100 mM KCl (88.58%). The lowest thymol content (39.26%) was observed with 200 mM CaCl 2 . These findings suggest that a 50 mM concentration of salts enhances thymol content. Salt treatments significantly influenced the chemical composition of M. citriodora , with the emergence of novel compounds in the essential oil under salt stress. The study highlights the impact of environmental stressors on metabolite profiles and suggests that adjusting salt concentrations could optimize essential oil quality in M. citriodora .