Biosynthesized silver nanoparticles ameliorate yield, leaf photosynthetic pigments, and essential oil composition of garden thyme (Thymus vulgaris L.) exposed to UV-B stress

The synthesis of silver nanoparticles has drawn attention due to their application in different scientific and industrial fields. Various types of green silver nanoparticles (AgNPs) are produced from medicinal and agricultural plant species. The effects of AgNPs on yield, selected morphological traits and biochemical composition of thyme (Thymus vulgaris L.) exposed to UV stress were explored in a factorial experiment based on a completely randomized design in three replications with two factors including biosynthesized AgNPs at three rates of 0, 50, and 100 mg L-1 and UV-B exposure for 0, 30 and 60 min in 2018-2019. The effect of UV radiation was significant on morphological and biochemical traits. The comparison of means revealed that as UV-B exposure time was increased from 0 to 60 min, shoot length, leaf dry weight, stem dry weight, and total dry weight were adversely influenced, but essential oil percentage was increased. The interaction of UV-B radiation and AgNPs significantly affected root length, root weight, chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, and essential oil yield. Meanwhile, UV-B enhanced the biochemical composition in some of the studied traits, but it is a sort of stress that decreased plant growth and yield. On the other hand, AgNPs had an alleviating impact on UV-B stress and improved plant growth and yield. Eventually, the interaction of the two factors improved growth and yield in addition to increasing biochemical compounds.