Foliar Application of ZnO Nanoparticles in Relation to Mineral Composition and Morphological Traits of Thyme (Thymus vulgaris L.)

Thyme (Thymus vulgaris L.) is a widely cultivated aromatic and medicinal plant valued for its culinary use, essential oils, and diverse bioactive compounds with nutritional and pharmaceutical significance. Zinc biofortification using nanoparticles (NPs) represents a promising approach for improving the nutritional value of aromatic and medicinal plants. This study evaluated the effects of foliar application of ZnO nanoparticles (ZnO NPs) on growth, biomass production, and mineral composition of thyme grown under controlled conditions. Plants were treated three times at seven-day intervals with ZnO NP suspensions at 0, 30, 60, and 90 mg L−1 (43; 86 and 129 µg Zn plant−1 respectively). Foliar Zn application did not significantly affect plant height, branching, shoot length, fresh or dry biomass, or derived morphological indices, although Zn60 showed the highest plant height and biomass per branch. In contrast, Zn accumulation showed a pronounced dose-dependent response. Zn concentration increased from 31.83 mg kg−1 in the control to 68.41 and 99.94 mg kg−1 under Zn60 and Zn90 treatments, representing approximately 2.15- and 3.14-fold higher Zn concentrations, respectively. Foliar treatments also modified the concentrations of several macro- and micronutrients, while Fe and Cu remained relatively stable. Zinc concentration was positively correlated with Fe, N, Cu, S, and Ca, while Fe and Cu concentrations remained relatively stable across treatments. In general, ZnO NP foliar application effectively enhanced Zn accumulation in thyme without significantly compromising plant growth, indicating its potential for agronomic biofortification.