Salinity stress is one of the most important challenges in agriculture systems. The present work was aimed to
evaluated the effects of saline irrigation, using different NaCl concentrations (0, 30, 60, and 90 mM), on growth,
physiological characteristics, phenolic compounds, and antioxidant activity of Thymus vulgaris and Thymus
daenensis, that are two of the most important medicinal and aromatic plants in Iran. An analytical method based
on HPLC-DAD has been developed to identify the main metabolites (mainly phenolic compounds) in thyme
extracts. The results indicated that concentrations of 60 and 90mM NaCl significantly decreased the plant dry
matter production by about 28 and 40% in T. vulgaris and 34 and 39% in T. daenensis, respectively, compared
with untreated plants. Application of NaCl also induced an increase in Na+content in shoots and leaves while the
K+ and Ca2+contents decreased with the salinity stress. Total phenolic content increased by around 20% after
the application of 60mM NaCl, compared with control plants. Also, an increase in leaf flavonoid content by
38.6% and 36.6% was observed in plants grown under salt stress conditions after the application of 60 and
90mM NaCl, respectively. Both investigated species were rich in phenolic acids, flavonoids, and phenolic
monoterpenes. Cinnamic acid was the major constituent in both species. This compound increased by 31.4% in
T. vulgaris treated with 60mM NaCl compared with the control. Concentrations of 60 and 90mM NaCl increased
significantly the amount of gallic and rosmarinic acids in T. vulgaris (25 and 31.6%, respectively) and T. daenensis
(20.4 and 27.6%, respectively). On the other hand, the mentioned NaCl concentrations did not significantly
change the content of caffeic, syringic, and vanillic acids in T. vulgaris. Interestingly, the higher amount of
chlorogenic acid (increase of 4.4%) in T. vulgaris was found under control condition, whereas in T. daenensis this
compound increased when salinity