Drought-induced physiological, biochemical, phytochemical, and yield-related trait variations among populations of Satureja rechingeri Jamzad

Satureja rechingeri Jamzad, an endemic aromatic species of Iran with high essential oil and phenolic potential, is of considerable pharmaceutical and ecological importance; however, its physiological and biochemical adaptations in response to drought stress across different populations remain insufficiently understood. This study aimed to evaluate population-level variation in growth, physiological performance, antioxidant defense systems, and phytochemical traits of four geographically distinct populations (Mehran, Dehloran, Shahiyun, and Lali) under three irrigation regimes (100%, 60%, and 30% field capacity) using a completely randomized factorial design. Drought stress significantly reduced growth-related traits, including biomass production, plant height, and leaf development, while markedly enhancing the accumulation of secondary metabolites and antioxidant capacity. Essential oil concentration increased under severe drought, whereas oil yield declined due to reduced biomass. Similarly, total flavonoid and phenolic content, FRAP antioxidant capacity, proline accumulation, and phenylalanine ammonia-lyase activity were strongly induced under water deficit conditions. Enzymatic antioxidants exhibited significant upregulation, indicating activation of an efficient reactive oxygen species detoxification system. Physiological traits, including chlorophyll and relative water content, decreased significantly under drought, while electrolyte leakage increased, reflecting membrane damage. Correlation and multivariate analyses revealed a clear trade-off between growth performance and stress-defense metabolism, with antioxidant enzymes and phenylpropanoid pathway activity playing central regulatory roles. Principal component analysis further confirmed a strong separation between well-watered and drought-stressed plants and highlighted substantial inter-population variability in adaptive responses. Among populations, Shahiyun showed superior growth maintenance and water-use efficiency, whereas Lali and Mehran demonstrated stronger biochemical defense activation under severe drought stress. Overall, the findings indicate that drought induces a coordinated shift from growth to defense metabolism in S. rechingeri and that significant intraspecific variation exists in stress adaptation strategies. These results provide valuable insights for selecting superior genotypes for cultivation and breeding programs in water-limited environments.