Various strategies elicited and modulated by elevated UV-B radiation and protectant compounds in Thymus species: Differences in response over treatments, acclimation and interaction

Nowadays, ultraviolet radiation, particularly from the ultraviolet-B (UV-B) range, is considered a regulating factor triggering a global response in the plants rather than a simple stressing factor. Predicted scenarios of climate change indicate the increasing trend of UV-B radiation in Mediterranean ecosystems as the center of origin of Thymus. The present study aimed to investigate the probable responses of three entirely different Thymus species in their natural habitats under elevated ultraviolet-B (UV-B), and to seek conditions that can induce desirable changes using UV-B radiation as an effective elicitor and protectant compounds as antioxidants. Altogether, under elevated UV-B radiation, the total amount of phenolic compounds was increased in all three species, while the total rate of alcoholic compound of linalool was decreased in Thymus fedtschenkoi. Principal components analysis suggested that the created scattering was caused by protectant compounds, especially under enhanced UV-B radiation. Despite the great differences in responses of each species to the applied treatments, there were similarities between the Thymus daenensis and Thymus fedtschenkoi species. However, Thymus vulgaris had the most distance. The most changes, both morphologically and phytochemically, were observed in Thymus fedtschenkoi. Thymus daenensis had the most accordance with the enhanced UV-B conditions, most likely because of growing on the southern slopes.