[Biological Effects of ZnO Nanoparticles as Influenced by Arbuscular Mycorrhizal Inoculation and Phosphorus...

ZnO nanoparticles (NPs) are widely used in many applications, such as plastics, ceramics, glass, cement, rubber, lubricants, paints, pigments, batteries, fire retardants, catalysts, and anti-microbial agents. They directly or indirectly enter aquatic and terrestrial environments through application, accidental release, contaminated soil/sediments, or atmospheric fallouts. When present in excess, ZnO NPs can induce phytotoxicity and reduce plant growth and yields. ZnO NPs can also cause Zn accumulation in edible parts of food crops, and then subsequently enter human bodies and pose a significant health risk. Arbuscular mycorrhizae are ubiquitous symbiotic associations in nature formed between arbuscular mycorrhizal (AM) fungi and most higher plants in terrestrial ecosystems. In addition to their well-known contribution to plant nutrient acquisition and growth, AM fungi can improve plant tolerance to various environmental stresses, but mycorrhizal effects vary with environmental conditions such as phosphorus status in both soil and plants. AM fungi have been shown to alleviate the negative effects of ZnO NPs and zinc accumulation in plants, however, the role of phosphorus fertilization has been neglected. A greenhouse pot culture experiment was conducted using maize as the test plant inoculated with or without AM fungus Funneliformis mosseae. Four levels of phosphorus (0, 20, 50 or 100 mg·kg^-1) and two levels of ZnO NPs (0 or 500 mg·kg^-1) were applied to pots. Shoots and roots were harvested separately after two months of growth. Mycorrhizal infection, plant biomass, P and Zn concentrations and uptake in plants, and soil DTPA-extractable zinc and pH were determined. The results showed that ZnO NPs did not significantly affect the growth of maize, but inhibited root mycorrhizal infection and plant phosphorus uptake, and led to the accumulation of zinc in plants. ZnO NPs and high phosphorus supply decreased root mycorrhizal infection, but AM inoculation significantly promoted plant growth under all phosphorus supply levels. Phosphorus application and AM inoculation increased soil pH, but reduced the bioavailability of Zn derived from ZnO NPs, decreased the translocation and accumulation of zinc in maize shoots, and thus produced beneficial effects on plants. In general, AM inoculation showed positive mycorrhizal effect, especially under low phosphorus conditions and addition of ZnO NPs. Our results showed for the first time that both AM fungi and phosphate fertilizer could help to mitigate soil pollution and the ecological and health risks posed by ZnO NPs.