Changes in growth characteristics and secondary metabolites in Thymus vulgaris L. under moderate salinity and drought shocks

In order to evaluation of phytochemical and growth changes from Thymus vulgaris L. under moderate abiotic stresses, an experiment was carried out at Imam Khomeini International University in a completely randomized design with three replications during 2016. The treatments consisted of drought (50% FC), salinity (100 mM NaCl) and non-stress control (100% FC). Root fresh weight, root dry weight, root length, main branch diameter, sub-branch diameter, sub-branch number, shoot dry weight, shoot fresh weight, plant height, relative water content and chlorophyll content were measured. Also, total phenols, flavonoids and anthocyanins were assayed in leaves, roots and stems by using spectrophotometer. Statistical analysis showed that drought and salinity had significant effects on morphological traits, except for shoot dry weight and number of lateral branches. Generally, morphological traits affected by drought stress in compared with non-stress condition; so that, plant height, main branch diameter, lateral branch diameter, root dry weight, root fresh weight and shoot fresh weight decreased under drought stress compared to non-stressed plants. Analysis of variance showed that stresses had significant effects on leaf and stem flavonoids and phenol contents. By contrast, there was no significantly difference between drought and saline stresses in terms of total flavonoids and phenol of roots. Mean comparisons showed that the amount of leaf phenols and flavonoids increased under drought stress in compared with non-stress condition. In conclusion, this study showed that drought and salinity were increased secondary metabolites in thyme, but the effect of salinity in increasing of secondary metabolites was lower than drought stress.