Toxic Effects Of Nano-zno And Nano Silver On Arbuscular Mycorrhizae

Being a hot frontier of global concern in the21st century, nanotechnology andnanomaterials are widely used, and widespread attention is paid to their safety andpotential risks at both home and abroad. As the most widely used nanomaterials,engineered nanoparticles (ENPs) exhibit certain biological toxicity to plants andmicroorganisms. Arbuscular mycorrhizal (AM) fungi represent a group of soilmicroorganisms closely associated with plant roots, which form AM symbiosis withmore than80%of higher plants in terrestrial ecosystems, and improve the mineralnutrition and stress resistance of host plants. However, the interaction between ENPSand arbuscular mycorrhizae and their effects on plant growth and nutrition still remainunclear. This research aimed to study the effects of different levels of ENPs (nano-ZnOand nano-Ag as target materials) on the growth and nutritional status of plants(soybean and sudan grass as test species) inoculated with or without AM fungus andthus provide a basis for safety evaluation of ENPs.1. A sand culture of greenhouse pot experiment was conducted to study theeffects of inoculation with or without the AM fungus Acaulospora mellea on growthand nutritional status of soybean plants and sudan grass under different nano-ZnOaddition levels (0,500,1000,2000, and3000mg/kg). The results showed that AMcolonization in soybean and sudan grass roots was not inhibited by nano-ZnO at the500and1000mg/kg addition levels, but was inhibited at the2000mg/kg additionlevel and higher, indicating a certain toxicity of nano-ZnO to AM fungi. Nano-ZnO atthe3000mg/kg addition level significantly inhibited the growth of soybean plants andsudan grass, displaying a substantial phytotoxicity. Compared to non-inoculationcontrol, AM fungal inoculation significantly promoted soybean growth only at the500mg/kg addition level, but the promoting effects to sudan grass were showed at the1000mg/kg addition level. Inoculation also significantly increased P, and K uptake byboth plants at the1000mg/kg addition level. 2. A sand culture of greenhouse pot experiment was conducted to study the effectsof inoculation with or without the AM fungus Acaulospora mellea on growth andnutritional status of soybean plants and sudan grass under different nano-Ag additionlevels (0,500,1000, and2000mg/kg). The results indicated that AM colonization insoybean and sudan grass roots was completely inhibited at all addition levels,indicating a marked toxicity of nano-Ag to AM fungi. Both soybean and sudan grassgrowth was inhibited at all addition levels, and the adverse effects were severer to thegrowth of roots than the shoots. Compared to non-inoculation control, AM fungalinoculation significantly reduced root Ag concentration of both crops at the500mg/kgaddition level and significant increased N, P, and K uptake in sudan grass but not insoybean plants at the2000mg/kg addition level.3. A sand culture of greenhouse pot experiment was conducted to study theeffects of inoculation with or without the AM fungus Acaulospora mellea on growthand nutritional status of sudan grass under different forms of Zn (nano-ZnO, micro-ZnO, ZnSO4·7H2O) added at the same level (500mg/kg). The results suggested that allforms of Zn did not have significant effects on mycorrhizal colonization rate and dryweight of sudan grass, indicating that they did not produce toxicity to AM fungi andplants at the addition level (500mg/kg). When applied at the concentration of500mg/kg, nano-ZnO could promote the N, P, and K uptake, while micro-ZnO and ZnSO4had varied effects on nutrients uptake, sometimes facilitating and sometimessuppressing, and ZnSO4addition treatment could increase Zn concentrationsignificantly. Compared to non-inoculation control, AM fungal inoculationsignificantly increased root Zn concentration and uptake (except control), andenhanced shoot dry weight and total dry weight of sudan grass (micro-ZnO inparticular).4. A sand culture of greenhouse pot experiment was conducted to study the effectsof inoculation with or without the AM fungus Acaulospora mellea on growth andnutritional status of soybean plants under different forms of Ag (nano-Ag, micro-Ag,AgNO3) added at the same level (500mg/kg). The results showed that AMcolonization in soybean roots and the growth of soybean plants were significantlyinhibited by nano-Ag and AgNO3at the500mg/kg addition level, and nano-Ag andAgNO3could increase root shoot ratio, and reduce the nutrients (N, P, K, Fe)uptake,while micro-Ag had no impacts at the same addition level. Compared to non- inoculation control, AM fungal inoculation could significantly increase soybean plantP and shoot K uptake under the treatment of micron-Ag, and remarkably reduce shootsAg uptake under the treatment of AgNO3.From our perspective, nano-ZnO could continually release Zn ions with toxiceffects, inhibit the uptake of mineral nutrients by plants roots, and then influence thegrowth of plants and AM fungi, which may be one of the main toxicity mechanisms ofnano-ZnO. However, the main toxicity mechanisms of nano-Ag are probably due tothe small particle size, and thus they could enter into the interior of the cell, andproduce shadowing effects. By improving mineral nutrition of host plants and evadingthe toxicity of heavy metals, AM fungi can exert their beneficial effects.