Ozone water irrigation treatment modulates growth performance, essential oils production and phenolic acid compounds in Thymus vulgaris L.

Thymus vulgaris L. is widely recognized for its medicinal and aromatic qualities, largely attributed to the diverse healing effects found in its essential oils and extracts. Factors such as genetic makeup, environmental variables, and agronomic practices play crucial roles in shaping the plant’s development, biomass production, and the quantity and chemical profile of its oils and extracts. Ozone water irrigation is emerging as a sustainable and novel approach in horticulture, offering potential to enhance plant development and stimulate the synthesis of key secondary metabolites and bioactive constituents. This study investigated the physiological, biochemical, and phytochemical responses of T. vulgaris to irrigation with ozone water at varying concentrations (0, 2.0, 4.0, 6.0, and 8.0 mg/L). Enhanced irrigation with ozone water significantly influenced plant growth metrics, including plant height, diameter, and biomass accumulation, with the most pronounced improvements observed at 6.0 and 8.0 mg/L concentrations. Although leaf dimensions remained unaffected, higher ozone levels promoted increased chlorophyll content and substantially elevated essential oil yield. Antioxidant-related traits, including total phenolic and flavonoid contents and FRAP activity, were notably amplified, whereas proline accumulation declined, indicating a reduction in oxidative stress. Despite elevated levels of oxidative stress markers (MDA, H₂O₂) under higher ozone water treatments, antioxidant enzymes such as CAT, POD, and SOD were significantly activated, particularly at 6.0 mg/L. Furthermore, GC–MS profiling revealed that while the proportion of beneficial compounds like acetovanillone and β-caryophyllene rose with ozone water application, key monoterpenoid phenols (e.g., thymol, carvacrol) declined at the highest ozone levels. The diverse responses of essential oil components, including monoterpenes and alcohols, suggest a dose-dependent modulation of secondary metabolism. These findings propose ozone-enriched irrigation as a potential agronomic strategy for enhancing growth and certain bioactive constituents of thyme, while cautioning its impact on specific oil components.