Study Of Ryegrass-Pakchoi Intercropping For Enhanced Remediation Of Uranium-Contaminated Soil

Soil radioactive contamination in uranium mines is a major problem faced by countries around the world.Phytoremediation is the main means to deal with soil contamination problem.However,the instability of single plant restoration of ecosystem has become a major bottleneck restricting the application of this technology.The optimized enhanced phytoremediation technology through intercropping is an effective way to alleviate this problem.In this paper,the uranium contaminated soil in uranium mines was taken as the research object,ryegrass and pakchoi were selected as the tested plants.The indoor potted simulation method was used to explore the remediation mechanism of ryegrass and pakchoi intercropping planting mode on uranium-contaminated soil.The results are as follows:（1）Effects of intercropping on the growth and uranium accumulation of ryegrass and pakchoiUnder the conditions of high and low levels of uranium-contaminated soil,the aboveground biomass of intercropping ryegrass and pakchoi increased by 20.18%-58.29%and root biomass increased by 18.22%-107.83%compared with that of monocropping,indicating that intercropping mode promoted the growth of ryegrass and pakchoi.The aboveground uranium content increased by 16.83%-42%and the root uranium content increased by 19.35%-37.32%compared to monocropping,indicating that the intercropping mode promoted the enrichment and accumulation of uranium in ryegrass and pakchoi.（2）Dynamic characteristics of uranium accumulation in intercropping of ryegrass and pakchoiSampling at different stages of plant growth,it was found that the aboveground biomass of ryegrass and pakchoi in intercropping mode reached the maximum at the 7^thand 6^thweek of the harvest period,which were 562.577 mg/pot and 344.507 mg/pot,respectively.In the middle and late growth stages,the aboveground and root uranium accumulations of ryegrass and pakchoi also reached a maximum value of 142.969 g/pot and 65.727 g/pot,respectively.Under intercropping mode,the uranium content in rhizosphere soil of ryegrass and pakchoi has significantly differences under different harvest times.During the first four weeks of the growth period,the uranium content in rhizosphere soil decreased slowly.From the fifth week,the uranium content in rhizosphere soil showed a significant decreasing trend,and decreased to 124.5 mg/kg and 145.167mg/kg in the near harvest period,which was about 40%lower than in the early growth period.（3）Effect of soil properties on uranium accumulation under intercropping patterns of ryegrass and pakchoiUnder the conditions of high and low levels of uranium-contaminated soil,compared with the control group,the intercropping pattern had certain effects on the p H,organic matter,and the soil microenvironment enzyme activity,microbial number,organic acid species and content in the rhizosphere soil of ryegrass and pakchoi.The results showed that the p H of rhizosphere soil under the intercropping mode was significantly reduced,in contrast,the peroxidase activity and urease activity in the rhizosphere soil were increased by 3-4 times compared with the control group.The number of bacteria,fungi and actinomycetes were also significantly increased compared to the control group.The types of organic acid of ryegrass and pakchoi in the rhizosphere soil under intercropping mode were more than those in other treatment groups.Uranium content in aboveground and rhizosphere of intercropping ryegrass and pakchoi was positively correlated with the main indicators in the rhizosphere soil microenvironment.（4）Analysis of mechanism of the interaction between ryegrass and pakchoi on uranium accumulationScanning electron microscopy analysis showed that the adsorption sites on plant surface and rhizosphere soil surface increased under intercropping mode.The energy spectrum diagram can be seen that the percentage of uranium content in rhizosphere soil accounted for total element content was 2.4%and 1.12%under intercropping mode,which were lower than monocropping,the uranium content in plant ash samples was the opposite.The analysis of infrared spectrum of rhizosphere soil showed that the vibrational intensity of most functional groups in rhizosphere soil decreased after intercropping,and the peak shape was more stable.The principal component analysis of different forms of uranium in rhizosphereed soils showed that the transformation of inert uranium to active uranium in rhizosphereed soils was obvious under intercropping mode,which promoted the absorption and accumulation of uranium by ryegrass and pakchoi.