Effects of Arbuscular Mycorrhizal Fungi on the Growth and Uptake of La and Pb by Maize Grown in La and Pb-Contaminated Soil

Abstract

A greenhouse pot experiment was conducted to investigate the effects of arbuscular mycorrhizal (AM) fungi Claroideoglomus etunicatum (CE) and Rhizophagus intraradices (RI) on AM colonization rate, biomass, nutrient uptake, C:N:P stoichiometry, and the uptake and transport of lanthanum (La) and lead (Pb) by maize (Zea mays L.) grown in La-and Pb-contaminated soils (combined La-Pb concentrations of 50, 200, and 800 mg·kg-1). The aim was to provide a scientific basis for the remediation of soils contaminated by rare earth elements and heavy metals. The results indicated that symbiotic associations were successfully established between the two isolates and maize, and the average AM colonization rate ranged from 26.7% to 95.8%. The increasing concentrations of La and Pb in soils significantly decreased the mycorrhizal colonization rate, biomass, and mineral nutrition concentrations of the maize, and significantly increased C:P and N:P ratios and the concentrations of La and Pb in shoots and roots of maize. The shoot and root dry weights of maize were significantly increased by 17.8%-158.9% with two AM fungi inoculations, while the P concentration of shoots and roots of the maize were significantly increased by 24.5%-153.8%. Inoculation with two AM fungi decreased the C:P and N:P ratios, consistent with the growth rate hypothesis. With AM fungi inoculation in three types of La-Pb co-contaminated soils, root Pb concentrations of the maize significantly increased by 51.3%-67.7%; shoot Pb concentrations of the maize significantly decreased by 16.0%-67.7%; and the transport rate of Pb from root to shoot of the maize decreased by 31.5%-54.7%. Meanwhile, inoculation with AM fungi significantly increased the shoot La concentrations in the maize grown in soils mildly contaminated with La-Pb, while it significantly decreased shoot La concentrations, increased root La concentrations of maize, and inhibited the transport of La from root to shoot of the maize grown in soils moderately contaminated with La-Pb, but had no significant effect in severely contaminated soils. The results showed that AM fungi had the potential to promote phytoremediation of soils contaminated with rare earth elements and heavy metals, with potential applications to revegetate such contaminated soil ecosystems.