Abstract:Plant inter-cropping shows strong potential for remediating uranium-contaminated soil. Uranium-contaminated soil was taken as research object, and pakchoi and ryegrass were selected for mono-cropping and inter-cropping treatment. Through pot experiment, the effects of different treatment system on plant biomass, uranium content in plant, and rhizosphere micro-environment (including organic acids, number of microorganism, enzyme activity, uranium content and uranium form in rhizosphere soil) of pakchoi and ryegrass under different systems were compared and analyzed. The rhizosphere remediation effect of plant inter-cropping system in uranium contaminated soil was explored. The results show that the inter-cropping system significantly increases the biomass and uranium content of each part of the plant compared with mono-cropping. Specifically, the above-ground biomass of pakchoi and ryegrass increase by 25.15% and 20.31%, respectively, and underground biomass increase by 11.80% and 20.86%, respectively, compared with mono-cropping. In addition, uranium accumulation in various parts of plants under inter-cropping system is significantly higher than that of mono-cropping, and the total uranium accumulation in pakchoi and ryegrass increase by 59.43% and 63.71%, respectively, while uranium content in rhizosphere soil decrease by 9.91% and 10.97%, respectively. The analysis of rhizosphere soil reveals that the inter-cropping system promotes the change of uranium morphology in the soil. Specifically, the proportion of inert uranium decreases while the proportion of active uranium increases compared with that of mono-cropping systems. Inter-cropping system increases the organic acid content in the rhizosphere soil of pakchoi and ryegrass. The contents of malic acid, acetic acid and fumaric acid in rhizosphere soil of pakchoi under intercropping system increase significantly compared with CK group, but are not significantly increase compared with mono-cropping system, increasing by 9.86%, 13.53% and 13.89%, respectively. Oxalic acid, acetic acid, citric acid and succinic acid in rhizosphere soil of ryegrass under intercropping system are significantly increased by 141.97%, 114.09%, 135.78% and 110.04% compared with mono-cropping and CK group, respectively. At the same time, the inter-cropping system decreases the pH value and organic matter content of the rhizosphere soil, and increases the catalase and urease activities of the rhizosphere soil of pakchoi and ryegrass. Specifically, the pH value and organic matter contents of rhizosphere and non-rhizosphere soil of pakchoi and ryegrass under inter-cropping system are significantly decreased compared with CK group and mono-cropping system, except that the pH value and organic matter contents of non-rhizosphere soil of pakchoi under inter-cropping system are not significantly decreased. The activity of catalase in rhizosphere soil of pakchoi and ryegrass in inter-cropping system is significantly increased than that in CK group, by 117.65% and 404.61%, respectively, and by 20.65% and 84.94% compared with that in mono-cropping system, but there is no significant difference. Urease activity in rhizosphere soil of pakchoi and ryegrass under inter-cropping system is significantly higher than that in mono-cropping and CK group, by 44.99%, 93.59%, 136.97%, 549.58%, respectively. In addition, the rhizosphere soil microbial quantity of pakchoi and ryegrass in intercropping system is increased compared with CK group and single cropping system. In the inter-cropping system, the rhizosphere soil microbial quantity of pakchoi and ryegrass increase significantly compared with CK group, but the rhizosphere soil bacterial and actinomycetes quantity of pakchoi just increase by 20.65% and 12.53%, respectively, and the rhizosphere soil fungal quantity increase by 61.88% compared with mono-cropping. The number of bacteria, actinomycetes and fungi in rhizosphere soil of inter-cropped ryegrass increase by 98.35%, 88.95% and 141.76%, respectively, compared with that of mono-cropping. The results show that the inter-cropping system may promote the secretion of organic acids in roots, change the rhizosphere microenvironment, increase the proportion of active uranium in rhizosphere, effectively increase plant biomass and uranium accumulation by plants, and then play a positive role in the restoration of uranium contaminated soil.