Effects of Different Concentrations of Lanthanum on the Growth and Uptake of Pb by Maize Grown Under Moderate Lead Stress

Abstract

A greenhouse pot experiment was conducted to investigate the effects of different concentrations of lanthanum (0 mg·kg-1, 50 mg·kg-1, 200 mg·kg-1 and 800 mg·kg-1) on growth, nutrient uptake, C:N:P stoichiometry, and La and Pb uptake by maize (Zea mays L.) under moderate lead stress (200 mg·kg-1) and evaluate the interaction of rare earth elements and heavy metals in the soil-plant system. The aim was to provide basic data and a theoretical basis for the remediation of rare earth element and heavy metal-co-contaminated soils in a rare earths mining area. The results indicate that the concentrations of CH3COONH4-EDTA-extractable La and Pb significantly increase and decrease, respectively, with increasing La concentrations of the soils. The shoot dry weights of maize significantly decreases by 17.90% to 81.17% and the root to shoot ratio of maize significantly increases by 21.74% to 86.96% with increasing La concentrations of the soils. With increasing La concentrations in soils, the root P contents of maize significantly decrease by 19.16% to 89.68%. The shoot P and N contents significantly decrease by 65.51% to 91.98% and 48.27% to 76.58%, respectively, when the exogenous application of La is 200 mg·kg-1 and 800 mg·kg-1, respectively. The increasing La concentrations in soils significantly increase the C:P and N:P ratios and shoot and root La concentrations of maize. The shoot and root Pb concentrations of maize significantly increase by 52.61% to 99.01% and 15.99% to 44.34%, respectively, with increasing La concentrations. Overall, the increasing La concentrations in soils significantly decrease the K, Ca, and Mg contents of maize. The results demonstrate that the presence of rare earth elements aggravates the phytotoxicity of heavy metals to plant and ecological risks. Further research should focus on the effects and mechanisms of rare earth elements on the heavy metal uptake by plants.