| The widespread adoption and over-exploitation of rare earths(REEs)has led to their continuous migration and pollution in the soil and water environment.Phytoextraction,a green and safe remediation tool,meets the current demand for environmentally friendly technologies,but its remediation efficiency depends mainly on the growth and enrichment characteristics of the selected plants.The unique complexing properties of natural organic acids(OAs)and their detoxifying effects are often used to enhance the enrichment of heavy metals in plants.Nevertheless,studies on the response of plants to rare earth elements are relatively homogeneous and few studies have been reported on the effects of organic acid enrichment on plant uptake and transport.In this study,we investigated the growth and accumulation characteristics of lanthanum(La)and yttrium(Y)under the combined stress of La and Y in the Phytolacca Americana L.and rice.On this basis,different ratios of malic acid(MA)and citric acid(CA)were applied to the culture solution,and the changes in biomass and root morphology of the Phytolacca Americana L.under La and Y stress,as well as the uptake and transport of La and Y and nutrients by the plants,were analysed to explore the effects of exogenous organic acids on the enhancement of La and Y extraction by plants and the optimal application ratio,with the aim of providing a scientific and theoretical basis for the enhancement and application of phytoremediation techniques in rare earth element polluted environments.The aim was to provide scientific theoretical basis and guidance for the enhancement and application of phytoremediation techniques in rare earth element polluted environments.The main findings of the study are as follows:(1)Different concentrations of La and Y stress showed hormesis effects on the growth of crop rice,with a significant promotion effect on stem and leaf biomass at a concentration of 100 μmol/L,with an increase of 10.53% compared to the CK group.At high concentrations of 700 μmol/L and 1000 μmol/L,rice leaves dried and yellowed,and root growth was particularly inhibited.In this study,rice was preferentially enriched in the light rare earth element La,and the presence of La at higher stress concentrations may have inhibited the uptake of heavy rare earth Y by the root system.Secondly,La and Y exposure led to a significant reduction in the upward transport of P in rice roots and inhibition of Ca,Mg and Na content in the roots.(2)Rare earth elements La and Y at the concentration level of 200 μmol/L promoted the elongation of the root system of the Phytolacca Americana L.,with a maximum increase of 18.75% compared with the group without La and Y application,and its growth was significantly better than that of rice.The accumulation of heavy rare earth element Y was higher than light rare earth element La in the stems and leaves of the Phytolacca Americana L.,but at high concentrations(> 500 μmol/L)of La and Y,the transport capacity of Y to the above ground was reduced due to the stress effect of both elements.The P content in the root system of the Phytolacca Americana L.tended to increase with La and Y exposure,and the Ka content in the stem and leaves was overall higher than in the non-rare earth treatment group,enhancing the translocation capacity to the ground.The Ca and Mg contents of the stem and foliage of the plant were negatively correlated with La and Y.Exposure to the rare earth elements La and Y prevented the uptake of the trace elements Mn,Zn and Cu by the root system,but significantly increased the Fe content of the root system.(3)All exogenous organic acids at appropriate concentrations alleviated the inhibitory effects of La and Y stress on the growth of the Phytolacca Americana L.Citric acid at a ratio of 3:1 had the strongest effect on the biomass and total root length of the Phytolacca Americana L.,while malic acid at a ratio of 2:1 significantly increased the root diameter of the Phytolacca Americana L.and made the plant grow stronger.(4)Exogenous addition of organic acids affected the uptake and translocation of rare earth elements La and Y by the Phytolacca Americana L.The highest La content in the upper part of the Phytolacca Americana L.was achieved with the addition of malic acid and citric acid at a ratio of 3:1,and the translocation coefficient increased,and the La content in the root system decreased by 4.43% ～ 37.63% compared with the group without the addition of organic acids,indicating that citric acid was mainly involved in the translocation of light rare elements La.Application of malic acid at a ratio of 2:1 significantly inhibited Y uptake by the roots,while increasing the above-ground translocation coefficient.The addition of exogenous organic acids caused a redistribution of heavy rare earth element Y and light rare earth element La within the plant,and was able to significantly increase the LREE/HREE partition coefficient of the plant,and the citric acid treatment was more significant than the malic acid treatment.The addition of exogenous organic acids significantly increased the content of P,Ka,Ca,Mg,Cu and Mn elements in the roots of the Phytolacca Americana L.,and did not affect the transport of these six elements to the aboveground.Malic acid was involved in the transport of Fe above ground,but correspondingly reduced the Fe content of the plant roots.In particular,the Mg content in the stem and leaf parts of the Phytolacca Americana L.was negatively correlated with the trace elements Fe、Mn、Cu、Zn,and there was a competitive relationship between the two types.It was also suggested that exogenous organic acids may mitigate the toxic effects of the rare earths La and Y on the Phytolacca Americana L.by maintaining the balance of Ca and Mg contents in the plant. |
PDF Full Text Request