The Performance And Mechanism Of Syngonium Podophyllum-Peperomia Tetraphylla Co-Planting For Enhanced Remediation Of Low Concentration Uranium Containing Wastewater

With the development of nuclear power-related industries,the demand for natural uranium in China is also increasing.However,the mining and processing of uranium will bring a series of environmental problems,especially the water pollution caused by uranium.Therefore,it is urgent to take effective measures to remediate uranium-containing wastewater.Phytoremediation technology has become a research hotspot in remediation of uranium-contaminated areas due to its advantages of safety and environmental protection.Some studies have found that co-planting of some plants can improve biodiversity,plant adaptability,plant anti-disturbance ability,make plants more efficient use of light,water and nutrients,and promote plant growth,make up for the deficiency of single plant remediation.To determine the effect of plant co-planting on the remediation of low concentration uranium-containing wastewater and to clarify the mechanism of plant co-planting system to enhance the remediation of low concentration uranium-containing wastewater.In this study,several plant co-planting systems were established.Based on the uranium removal rate,the plant co-planting system(Syngonium podophyllum-Peperomia tetraphylla)with the highest uranium removal rate was screened out,and the low concentration uranium-containing wastewater remediation experiment was carried out with it.The variation of uranium content in water with time and the influence of uranium concentration on the remediation efficiency of the plant co-planting system were studied.The subcellular distribution,valence,chemical forms of uranium in plants and changes of functional groups in plant roots were analyzed by differential centrifugation,XPS,sequential extraction methods,and FT-IR.Untargeted metabolomics of plants were studied by LC-MS to reveal the molecular mechanism of plant interactions.The results showed that plant co-planting can promote the remediation of uranium-containing wastewater in the range of 0.5～2.0mg/L,and when the content of uranium is 1.0 mg/L,the promoting effect is most significant.compared with the corresponding single phytoremediation system,the removal rate of uranium in 1.0 mg/L uranium-containing wastewater by the co-planting remediation system of Syngonium podophyllum-Peperomia tetraphylla increased by 4.70% and7.00% respectively.The translocation factor,bioaccumulation factor,and bioaccumulation of Syngonium podophyllum are increased by 132.20%,63.89%,and 63.89%,respectively(6.00%,37.27%,37.27% for Peperomia tetraphylla).Compared with the single plant system,the total amount of ethanol extracted uranium and deionized water extracted uranium in the plant roots of the two systems decreased by 10.30% and7.17%,respectively.XPS results show that the interaction between plants could be restrained Peperomia tetraphylla root for the reduction of U(Ⅵ).Besides,the subcellular distribution results show that uranium in plants is mainly distributed in cell walls(54.44%～66.52%)and soluble components(23.85%～32.89%).Metabolomics analysis showed that 291 metabolites were differentially expressed between the co-planting Peperomia tetraphylla and the single Peperomia tetraphylla remediation system.There were 284 differentially expressed metabolites between the co-planting system Syngonium podophyllum and the single Syngonium podophyllum system.A total of 10 different metabolic pathways were significantly enriched,which were mainly involved in the anabolism of amino acids,organic acids,sugars and other substances.The above results reveal that Syngonium podophyllum-Peperomia tetraphylla co-planting increased the biomass of the two plants effectively,and the bioaccumulation(BA),translocation factor(TF),and bioaccumulation factor(BCF)of uranium in plants were increased significantly,so as to improve the uranium removal rate of low concentration uranium-containing wastewater.The main mechanism is as follows:(1)The co-planting of Syngonium podophyllum-Peperomia tetraphylla changed the chemical forms of uranium inplants,reduced the proportion of uranium extracted from deionized water and ethanol in the two plants,promoted cell wall immobilization and vacuole separation,and lowered the toxicity of uranium to plants.(2)Syngonium podophyllum-Peperomia tetraphylla co-planting could restrain the reduction of U(VI)by the roots of Peperomia tetraphylla,and facilitate the transfer of uranium from roots to shoots.(3)The interactions between plants can up-regulate the expressions of amino acids,sugars and organic acids,and promote the growth of plants and the transport of uranium.