Soil salinity is one of the major limiting factors of medicinal plant performance and may affect their properties and chemical constituents. Although various reports have suggested the light quality-mediated modulation of growth and metabolism, little is known about physiological and phytochemicals aspects of light intensity on medicinal plants. In the present study, a factorial experiment as a randomized complete block design with three replicates was conducted to investigate the effects of salinity stress and light intensity on tarragon plants grown in pots at outdoor conditions. The experimental treatments consisted of NaCl salt stress at three levels (0, 60, and 120 mM) and different light intensities (full light, 75% of sunlight, and 50% of sunlight). According to the results, salinity led to a reduction in plant height, shoot dry weight, relative water content (RWC), and chlorophyll content compared to control conditions. While low light intensity improved the above mentioned characteristics. However, the interaction effect of salinity (60 mM) and low light intensity significantly increased anthocyanin and chlorophyll contents, and dry weight. Overall, tarragon yield can be improved at 75% of light intensity and moderate salinity by increasing the synthesis of photosynthetic pigments and phenolic compounds as protective substances. Essential oils examined here were particularly rich in methyl chavicol (68.39–79.02%), camphene (0.26–6.28%), β-pinene (0.24–5.21%), and trans-β-o-cymene (1.49–4.53%).
