Objective: Nitrogen is a critical macronutrient for plant growth and development, and the application of nitrogen in nanoscale form has emerged as a promising strategy to enhance nutrient use efficiency and crop productivity. This study investigated the effects of different concentrations of nitrogen nano-fertilizer on some traits of three medicinal plants; Withania coagulans, Echinacea purpurea, and Valeriana officinalis, cultivated in an aeroponic system. Methods: The trials were performed in a completely randomized design using five replications. The foliar application of nitrogen nano-fertilizer (0, 1000, and 2000 mg L-1) was performed at 20, 40, and 60 days after transferring to the aeroponic system. Morphologic traits including fresh and dry weights of shoots and roots as well as the height of shoots and roots, and number of leaves were measured. Also, photosynthetic pigments consist on chlorophylls (a and b), and carotenoids, were recorded. Results: The results demonstrated a dose-dependent effect of nitrogen nano-fertilizer on all measured traits across the three species. In Valeriana officinalis, the highest concentration significantly increased root length, leaf number, shoot dry weight, plant height, and root dry weight, compared to the control. Similarly, Echinacea purpurea and Withania coagulans showed significant improvements in vegetative growth and biomass accumulation, although the magnitude of response varied among species. Photosynthetic pigments were also enhanced under nano-fertilizer treatment, with chlorophyll a, chlorophyll b, and carotenoids reaching their highest values at 2000 mg L-1 in all species, suggesting improved photosynthetic capacity and photoprotection. Comparison of these species indicated that Valeriana officinalis had the highest growth improvement, while Echinacea purpurea showed more root development and pigment accumulation. Conclusion: Nitrogen nano-fertilizer proved to be an effective tool for promoting vegetative growth, biomass accumulation, and photosynthetic efficiency in the medicinal plants grown under controlled aeroponic conditions. This study provided insights for the sustainable cultivation of high-value medicinal crops and supports the use of nanoscale nutrient to improve plant productivity.
