纳米氧化锌和接种丛枝菌根真菌对大豆生长及营养吸收的影响

纳米氧化锌是应用最广的人工纳米颗粒(nanoparticles,NPs)之一,具有一定生物毒性。丛枝菌根(arbuscular mycorrhizal,AM)真菌能与陆地上80%以上的高等植物形成丛枝菌根共生体,并能改善宿主植物矿质营养,提高其抗逆性。然而纳米ZnO与丛枝菌根的关系尚不清楚。通过温室沙培盆栽试验,研究了施加不同水平纳米ZnO(0、500、1000、2000、3000 mg/kg)和接种AM真菌Acaulospora mellea对大豆生长及营养状况的影响。结果表明,3000 mg/kg的纳米ZnO显著抑制大豆植株生长,表现出植物毒性,在其他水平时没有显著影响。纳米ZnO在施加水平500、1000 mg/kg时没有抑制AM真菌对大豆根系的侵染,但是高施加水平(2000 mg/kg)时对AM真菌产生毒害,几乎完全抑制大豆根系菌根侵染。接种AM真菌仅在500 mg/kg纳米ZnO时显著促进大豆生长,增加大豆植株对P、K、N的吸收,降低根系Zn含量。纳米ZnO可能会持续释放锌离子,并抑制大豆根系对矿质营养元素的吸收,从而产生生物毒性,而AM真菌与大豆根系的共生可起到有益作用。

Effect of ZnO nanoparticles and inoculation with arbuscular mycorrhizal fungus on growth and nutrient uptake of soybean

ZnO nanoparticles (NPs) are widely used in cosmetics, personal care products, paints, electronic devices, catalysts, anti-microbial agents, etc. These compounds enter aquatic and terrestrial environments and the atmosphere through direct application, accidental release, contaminated soil/sediments, or atmospheric fallouts. Increasing attention has been directed toward their environmental fate and behavior, and especially their biological effects on crops and microorganisms in agricultural ecosystems. Recent studies have shown that, when in excess, ZnO NPs can cause phytotoxicity and declines in soil quality, reduce plant biomass and yields, result in excess Zn accumulation in plants, especially in edible parts of food crops, and subsequently enter human bodies through the food chain, posing a health risk. Therefore, techniques to reduce the potential toxcity and risk caused by ZnO NPs need to be explored. Arbuscular mycorrhizal (AM) fungi represent a group of soil microorganisms widely associated with plant roots, forming a mutualistic symbiosis with more than 80% of higher plants in terrestrial ecosystems. They play important roles in improving mineral nutrition and resistance of host plants to environmental stress, contribute to nutrient cycling of C, N, P, and other elements, and maintain soil health and plant community stability and productivity. AM fungi have positive effects on the tolerance of host plants to heavy metal stress through direct and indirect mechanisms. Therefore, arbuscular mycorrhizae could putatively contribute to reducing phytoxicity induced by metal or metal oxide NPs. However, the interactions between NPs and arbuscular mycorrhizae remain unclear. A sand culture pot experiment was conducted to study the effects of inoculation with or without the AM fungus Acaulospora mellea on growth and nutritional status of soybean plants under different ZnO NPs addition levels (0, 500, 1000, 2000, and 3000 mg/kg). Shoots and roots were harvested separately after 12 weeks of growth in a greenhouse. Mycorrhizal colonization, plant dry weights, P, K, N, and Zn concentrations and uptake were determined. Results showed that ZnO NPs at 3000 mg/kg addition level significantly inhibited the growth of soybean plants, displaying a substantial phytotoxicity but had no significant effect at other addition levels. AM colonization in soybean roots was not inhibited by ZnO NPs at the 500 and 1000 mg/kg addition levels, but it was almost completely inhibited at the 2000 mg/kg addition levels and higher, indicating a marked toxicity of ZnO NPs to AM fungi. Addition of ZnO NPs led to significant Zn accumulation in plant tissues, especially in roots. Compared to non-inoculation control, AM fungal inoculation significantly promoted soybean growth only at the 500 mg/kg addition level. Inoculation also increased P, K, and N uptake, and reduced root Zn concentration at low ZnO NPs addition levels. ZnO NPs could continually release zinc ions with toxic effects and inhibit the uptake of mineral nutrients by soybean roots, which may be one of the main toxicity mechanisms of ZnO NPs. Our results reveal that AM symbiosis can attenuate ZnO NPs-induced toxicity in plants and symbiotic fungi, which will aid in understanding of the interactions of engineered nanomaterials with plants and soil microorganisms in terrestrial ecosystems.