Effects of Foliar Application of Zinc Oxide Nanoparticles on Traits of Several Medicinal Plants Under Aeroponic System Conditions

As a micronutrient, zinc (Zn) plays an essential role in various physiological processes of plants. Here, acclimatized samples of valerian (Valeriana officinalis L.), chicory (Cichorium intybus L.), withania (Withania. coagulans) and purple coneflower (Echinacea purpurea L.) were evaluated under aeroponic system conditions in order to explore the effects of zinc oxide nanoparticles (ZnO NPs). The plants were foliar sprayed with ZnO NP biofertilizer (0, 1, 2 and 3 g L-1) for 20, 40 and 60 days after transplanting. The experiments were performed based on a completely randomized design with five replications. The valerian showed that 3 g L-1 ZnO NPs caused the highest plant height, root length, leaf number per plant, root volume per plant, as well as fresh and dry weights of roots and shoots. The mean values in chicory showed that the plants that were treated with ZnO NPs (3 g L-1) had the highest amount of biomass and photosynthetic pigments. Based on the results of mean values in purple coneflower, ZnO NPs (3 g L-1) caused the largest increase in morphological values. Furthermore, comparing the mean values in the withania showed that the highest plant height, root length, leaf number per plant, root volume per plant, fresh and dry weights of roots and shoots were observed in plants treated with 3 g L-1 ZnO NPs. Therefore, Zn is considered as an essential micronutrient in the growth of these plants and could be prepared in nanosized form.