Synergistic Enhancement Of Phytoextraction Of Uranium Using Lolium Perenne L. From Soil By Aspergillus Niger Fermentation Broth And Calcium Peroxide

Uranium topsoil has low uranium grade but large reserves.Because it is located on the surface,it poses potential threats to the ecological environment through surface runoff and underground seepage.The development of high-efficiency and green technologies for the extraction of uranium from topsoil is of great significance for improving the supply capacity of natural uranium and protecting the ecological environment.Phytoextraction has the advantages of simple operation and low cost,which can be used for the recovery of low-grade surface resources.For U?IV?-containing uranium topsoil,insoluble U?IV?must be oxidized to soluble U?IV?in order to be available to plants and be efficiently extracted by plants.In this study,Greenhouse soil culture experiments were conducted to investigate the phytoextraction of uranium from topsoil by Lolium perenne L..The effects of addition of CaO₂,Aspergillus niger fermentation broth and their combination on physiological characteristics of Lolium perenne L.,enhancement of uranium phytoextraction and rhizosphere soil microbial community were investigated.The main achievements are summed up as follows:?1?The separate application of high dosed A.niger fermentation broth had a stimulative effect on Lolium perenne L.growth whereas the separate application of high dosed CaO₂,the joint application of high dosed CaO₂ and A.niger fermentation broth both gave an inhibitive effect.The application of A.niger fermentation broth and high-dose CaO₂decreased the leaf water content.The application of CaO₂ decreased the soluble sugar in leaves,while the application of medium and high doses of fermentation broth increased it.Furthermore,all the treatments resulted in an increased accumulation of soluble protein in Lolium perenne L.leaves,among which the separate addition of 40 mL/kg fermentation broth generated the highest content,increasing by 511.11%compared to the control.The application of A.niger fermentation alone led to the decrease in superoxide dismutase?SOD?activity and malondialdehyde?MDA?contents in Lolium perenne L.leaves,while the separate application of high dosed CaO₂,joint application of high dosed CaO₂ and A.niger fermentation broth both caused a reveres effect.The peroxidase?POD?activity of plant leaves in all treatment groups was increased.In the case of the separate application CaO₂,A.niger fermentation broth,and the combined application high-dose CaO₂+fermentation broth,the plant leaf catalase?CAT?activity decreased significantly.?2?The uranium concentration in the soil solution and uranium phytoextraction raised in all the treatments,in which the combined application at 1 g/kg CaO₂ and 20 mL/kg fermentation broth showed the best effect.Uranium content in the ash of Lolium perenne L.aboveground increased by 622.80%,and the total accumulation of uranium increased by 483.65%against the control.?3?Through the separate application of 2 g/kg CaO₂,40 mL/kg A.niger fermentation broth,and the combined application of 1 g/kg CaO₂+20 mL/kg A.niger fermentation broth,the Lolium perenne L.rhizosphere microbial community changed,and the fungal abundance increased.The dominant rhizosphere soil fungi are Mortierella,Chaetomium and Fusarium.After adding additives,the proportion of fungi such as Fusarium and Trichoderma rose,in which the unique fungal phylum Mucoromycota appeared when 1 g/kg CaO₂+20 mL/kg fermentation broth were jointly applied.Dominant bacterial genera are Sphingomonas,Thiobacillus,and Lysobacter,in which the proportion of bacterial such as Thiobacillus rose by the combined application of 1 g/kg CaO₂+20 mL/kg fermentation broth.And the bacterial phylum Lentisphaerae appeared in rhizosphere soil with the application of 2 g/kg CaO₂.