• Mild salinity had greater effect on volatile contents than biostimulants. • Biostimulants enhanced phenolics (up to 98%) in common thyme. • Biostimulant application enhanced phenolic and volatile compound accumulation. Common thyme ( Thymus vulgaris L.) is a widely cultivated aromatic herb that is valued for its high content of phenolic and volatile compounds, which contribute to its nutritional and sensory quality. A range of agronomic strategies have been investigated for the purpose of enhancing the quality of common thyme, including the implementation of mild abiotic stress. In this study, mild salinity stress was combined with four biostimulants to evaluate their effects on the phenolic and volatile profiles of common thyme. The identification of 14 phenolic compounds and 32 volatile compounds was achieved through the utilisation of HPLC-MS and GC-MS analysis, respectively. Salinity exhibited a significant effect on the total phenolic content, with a marked increase in comparison with the control. The incorporation of biostimulants served to augment phenolic accumulation, with Protifert® LMW exhibiting the most pronounced effect, resulting in an escalation of the total phenolic content by 44–98% relative to the control. It was established that rosmarinic acid and luteolin-3- O -glucuronide were the most responsive compounds. Concurrently, the volatile profile exhibited a substantial response to biostimulant application. The Delfan Plus and Protifert® LMW treatments resulted in the highest total volatile contents, with Delfan Plus reaching 167.31 mg kg-1 FW, corresponding to increases of 129% and 52% compared with saline and non-saline conditions, respectively. Overall, mild salinity stress modulated phenolic and volatile metabolism in common thyme, while selected biostimulants enhanced metabolite accumulation. These findings underscore the efficacy of integrating controlled salinity stress with biostimulant application as a strategy to enhance the phytochemical quality of common thyme.
Zamljen et al. (Wed,) studied this question.