Due to their small size and high reactivity, ZnO nanoparticles (NPs) can increase yarrow yields and control worms, enhance the activity of mustard cells and improve their antioxidant capacity, and promote plant growth. Meanwhile, there are data showing that ZnO NPs may inhibit the root formation of plants toxic to wheat. Due to the wide variety of research methods, conditions, NPs synthesis and properties, it is impossible to fully analyze and predict the effects of NPs concentrations on plants.

This study explored the treatment of wheat seeds with different concentrations of engineered ZnO NPs with average particle sizes of 40 and 300 nm. After the treatment, we measured the germination energy and root/shoots length of young wheat seedlings.

The results showed that 40 nm ZnO NPs had a promoting effect on wheat seeds when the concentration of NPs was 1-100 mg per liter. At higher concentrations (100-1000 mg per liter), the inhibitory effect on wheat roots continued to increase. For 300 nm of ZnO, the promoting effect was smaller compared to that of 40 nm ZnO NPs. In contrast, the larger 300 nm ZnO NPs induced a consistently smaller promoting effect across the tested concentrations compared to the 40 nm particles, indicating that nanoparticle size played a critical role in determining biological activity and phytotoxicity thresholds. These findings underscore the necessity of precise size and concentration control in agricultural nanoparticle applications.