Thymus vulgaris L., a member of the Lamiaceae family, is one of the most widely used medicinal and aromatic plants. This experiment aimed to investigate the effects of CO2 enrichment at 350, 700, and 1000 mg/L (C1, C2, and C3) combined with supplementary lighting photoperiods of 12, 16, and 20 hours (L1, L2, and L3) on several attributes of T. vulgaris. Measurements included fresh and dry weights of plant organs, photosynthetic pigments, essential oil quantity and composition, as well as the activity of catalase, ascorbate peroxidase, and polyphenol oxidase. The antioxidant capacity, along with the assessment of phenolic compounds and flavonoid content, was also conducted. The L3C3 treatment significantly improved several parameters, including fresh weight, dry weight, plant height, chlorophyll a, chlorophyll b, essential oil content, carotenoids, phenolic compounds, flavonoids, and antioxidant activity. These showed respective increases of 110%, 276%, 82%, 63%, 63%, 160%, 45%, 68%, 13%, and 45%. Additionally, the L3C1 treatment significantly enhanced peroxidase activity by a factor of 108%. Furthermore, under the L3C1 treatment, catalase, superoxide dismutase, and polyphenol oxidase activities increased by 37%, 50%, and 73%, respectively. |