Soil salinity critically compromises the cultivation of high-value medicinal plants. This study evaluated the morpho-physiological and phytochemical responses of four geographically distinct Satureja khuzistanica Jamzad populations (Havian, Dorgar, Garmabad, Paalam) to incremental NaCl salinity (0, 75, 150 mM). Salinity exposure triggered a concentration-dependent decline in key growth parameters, including plant height, leaf area, and dry biomass. Among the populations, Dorgar and Garmabad showed the strongest growth reductions. All populations activated defense mechanisms at the physiological level, including significant accumulation of osmolytes (proline and γ-Aminobutyric acid) and enhanced enzymatic and non-enzymatic antioxidant activities. Notably, essential oil concentration increased under salinity in all populations, reaching a maximum in Dorgar (4.10% at 150 mM), although total oil yield per plant declined due to reduced biomass. Carvacrol remained the dominant constituent (91–98%) with minor population-specific variations. Based on an integrated assessment of growth performance and physiological resilience, Paalam emerged as the most tolerant population, closely followed by Havian, whereas Dorgar and Garmabad were the most sensitive. These findings reveal significant biochemical plasticity in S. khuzistanica. While all populations experienced reductions in growth under high salinity, tolerant populations (Paalam and Havian) retained relatively higher growth compared to sensitive populations, alongside enhanced antioxidant activity and stable essential oil quality. These results underscore the potential of utilizing specific, resilient populations for the sustainable cultivation of S. khuzistanica in marginal, salt-affected lands
