Phytoremediation Of Uranium Contaminated Soils By Macleaya Cordata And Salicaceae In Intercropping Pattern

The uranium mill tailings impoundment contains radioactive wastes such as waste slag and waste liquids with very high uranium content.Under the effect of rain,they can contaminate the surrounding soil with surface runoff,cause long-term low-dose radiation damage to the environment,and eventually affect human health.through the food chain.Phytoremediation methods have the advantages of low cost,no secondary pollution,and little disturbance to the environment.There are great differences in tolerance,absorption and accumulation of uranium among different plants.However,the monocropping phytoremediation of uranium-contaminated soil has the problems of low restoration efficiency and being easily disturbed by the surrounding environment.The intercropping pattern of plants is a safe production method that can increase land use efficiency and produce complementary effects between two plants.It can also be used for the restoration of soils contaminated with low concentrations of heavy metals.The Salicaceae cultivation experiment aims to explore the potential of remediating uranium contaminated soil.The experimental results show that,the aerial and underground part of uranium accumulation in the Salicaceae is 37.82 mg/kg and 375.68 mg/kg,respectively.Salicaceae can effectively accumulate the uranium in the waste soil.The chemical form of uranium in the rhizosphere soil of Salicaceae was changed,the proportion of organic-bound U complexing uranium decreased by 32.41 %,and exchangeable U increased by 219.49%,and the bioavailability of uranium in rhizosphere soil increased.Salicaceae biomass is large and can be harvested multiple times,and is suitable as a uranium accumulator.In this study,experiments were conducted to screen the uranium accumulators including Helianthus annuus,Macleaya cordata and Salicaceae.All of them were planted in monoculture and intercropping patterns to remediate uranium contaminated soil.The [UO2(NO3)2·6H2O] solution was added to the campus soil matrix to simulate uranium contaminated soil and to carry out experiments on remediate uranium contaminated soil by greenhouses.Research purposes,Compare the difference in uranium enrichment capacity between plants in the intercropping and monocropping patterns,and screen the best intercropping pattern.Analyze the microbial community characteristics in monocropping and intercropping plant rhizosphere soils and explore the influencing factors of different microbial communities on plant accumulation of uranium.Study the factors affecting the ability of organic acids to accumulation uranium from plants,the types and contents of organic acids in the rhizosphere soil of different planting patterns are studied.Provide a theoretical basis for the intercropping remediation of uranium contaminated soil,study the characteristics of uranium chemistry species and the mechanism of intercropping patterns.The main research results show that,compared with monocropping,the remediation efficiency was the highest during the intercropping between Macleaya cordata and Salicaceae.The uranium accumulation was increased by 183.50% and 24.93%,respectively,and the accumulation coefficient was increased by 177.44%.and 46.41 %.In Macleaya cordata and Salicaceae intercropping,the proportions of tolerant bacteria acidobacteria,growth-promoting bacteria bradyrhizobium and excreting organic acids bacteria aspergillu significantly increased.The acidobacteria and bradyrhizobium improved their tolerance and bioaccumulation abilities for uranium,and the organic acids excreted by aspergillu could chelate with uranium,resulting in chelates formed for plants accumulation.Among the organic acids in the rhizosphere soil Macleaya cordata and Salicaceae intercropping,oxalic acid and malonic acid are the main components of organic acids,and the contents are 397.491 mg/L and 197.731 mg/L,respectively.They can change the rhizosphere environment,increased plant accumulation and transfer uranium upwards.Compared with the monoculture pattern,the proportion of residual uranium in the rhizosphere soil Macleaya cordata and Salicaceae intercropping were almost unchanged,organic-bound U decreases by 11.59 % to 14.54 %,and exchangeable U increases by 33.47 % to 47.63 % which plants can directly used.The increasing exchangeable uranium is more conductive to plants accumulate uranium.