Study Of Aspergillus-Enhanced Ryegrass In Remediation Of Pb,Zn,Cu And Cd Compound Polluted Farmland Soil

Heavy metal pollution in soil is one of the products of the rapid development of global industrialization and urbanization in recent years.Phytoremediation is a new method of in-situ remediation that green plants absorb heavy metals from soil and enrich them into overground tissues.It is considered as a non-secondary pollution and sustainable development method.Soil rhizosphere microorganisms can promote the growth of plants under heavy metal stress in many ways and improve the efficiency of phytoremediation of heavy metal contaminated soil.In this paper,Aspergillus niger TL-F2(A.niger TL-F2)and Aspergillus flavus TL-F3(A.flavus TL-F3)were selected to study the effects of different concentrations of Pb,Zn,Cu and Cd on the contents of indole-3-acetic acid(IAA),1-aminocyclopropane-1-carboxylic acid(ACC deaminase),siderophores and phosphate solubilization.The detoxification mechanism of two strains of ryegrass against Cd was studied by hydroponic experiment.The effects of two strains on the physiology and heavy metal enrichment of ryegrass were studied by rhizosphere bag culture experiment,and the changes of rhizosphere soil microbial community were analyzed by 16 S r DNA high-throughput sequencing.The main findings are as follows:1.Without the addition of exogenous heavy metals,A.niger TL-F2 secreted16.40 mg/L of IAA,3.47 mg/L of ACC deaminase,57.74% of the capacity of siderophores production and 89.16 mg/L of phosphate solubilization.A.flavus TL-F3 secreted 18.65 mg/L of IAA,3.72 mg/L of ACC deaminase,21.48% of the capacity of siderophores production and 176.92 mg/L of phosphate solubilization,respectively.With the increase of Pb,Zn,Cu and Cd concentrations,the four probiogenic characteristics of the two strains all decreased to different degrees(in which Pb stimulated A.flavus TL-F3 to secrete ACC deaminase and iron production vector,while Cd and Zn stimulated A.flavus TL-F3 to secrete IAA and siderophores production).2.Under the stress of Cd,both strains of Aspergillus promoted the growth of ryegrass,and the maximum Cd content in the overground was reduced by 51.00%,and the maximum Cd content in the root was reduced by 44.01%.In ryegrass subcells,Cd was mainly distributed in cell wall component F1(1.50 mg/kg-5.98 mg/kg)and soluble component F3(2.60 mg/kg-10.17 mg/kg),and a small part was distributed in organelle F2 component(0.71 mg/kg-3.77 mg/kg).After inoculation,the Cd content of F3 in overground parts increased by 5.70%-9.87%,and that of F1 in overground parts decreased by 9.05%-23.52%.The content of Cd in root F1 increased by9.61%-43.51%,and that in root F3 decreased by 17.47%-26.39%.3.Both strains of Aspergillus could improve the activity of antioxidant enzymes(SOD,POD and CAT)in ryegrass,reduce the content of MDA,and alleviate the toxic effect of heavy metals on ryegrass.The two strains changed the extraction efficiency of Pb,Zn,Cu and Cd by ryegrass,the aboveground Pb absorption increased by12.73-89.59%,the root Pb absorption decreased by 2.50%-26.19%,the ryegrass Zn and Cu absorption increased by 0.13%-31.11% and 0.53%-53.14% respectively,the ryegrass Cd absorption decreased by 4.72%-37.96% after planting 30 days,and increased by 4.26%-54.17% after planting 60 days.The two strains reduced the content of heavy metals in soil.The content of Pb,Zn,Cu and Cd in soil decreased by0.92%-20.53%,0.26%-24.56%,1.78%-33.01% and 1.23%-40.95%,respectively.4.High-throughput sequencing results showed that 20 known phyla and 314 known bacterial genera were detected in the samples.Five dominant phyla were detected: Proteobacteria,Bacteroidetes,Actinobacteria,Gemmatimonadetes and Patescibacteria.Proteobacteria was the first dominant phylum,accounting for 35.86%to 51.83%.Compared with CK treatment,the abundance of the first dominant bacteria in other treatments increased by 13.58% to 44.53%.There were 10 species of dominant rhizosperm bacteria treated by CK,N,F and NF,respectively:Sphingomonas,Chitinophagaceae,Saccharimonadales,Rhodanobacter,Chujaibacter,Longimicrobiaceae,Gemmatimonadaceae,Gemmatimonas,Lineage＿IIb and Haliangium.There are 8 dominant bacteria in the treatment of rhizosphere soil:Sphingomonas,Chitinophagaceae,Saccharimonadales,Rhodanobacter,Chujaibacter,Longimicrobiaceae and Gemmatimonadaceae.The abundance of Sphingomonas and Chitinophagaceae increased by 5.99%-124.13%,and that of Chitinophagaceae increased by 0.12%-31.92%(except for the 15.48% reduction of Chitinophagaceae by RN treatment)compared with that of the empty treatment.