Effects of short-term soil exposure of different doses of ZnO nanoparticles on the soil environment and the growth and nitrogen fixation of alfalfa.

The extensive application of nanomaterials has increased their levels in soil environments. Therefore, clarifying the process of environmental migration is important for environmental safety and human health. In this study, alfalfa was used to determine the effects of different doses of ZnO nanoparticles (NPs) on the growth of alfalfa and the soil environment. Results showed that the alfalfa biomass was inversely proportional to the exposure concentration of ZnO NPs. The Zn concentration in the alfalfa tissue and the exposure dose presented a significant positive correlation. A high concentration of ZnO NPs decreased the nitrogen-fixing area of root nodules while the number of bacteroids and root nodules, which in turn affected the nitrogen-fixing ability of alfalfa. At the same time, it caused different degrees of damage to the root nodules and root tip cells of alfalfa. A high dose of ZnO NPs decreased the relative abundance and diversity of the soil microorganisms. Therefore, short-term and high-dose exposure of ZnO NPs causes multiple toxicities in plants and soil environments.