Study On The Mechanism And Application Of Compound Microbial Inoculum For Enhanced Plant Extraction Of Heavy Metals

Frequent human activities have introduced a large number of heavy metal pollutants into the soil,which has adverse effects on human health and food safety production.The restoration of contaminated soil has become an urgent problem to be solved.Due to the limitations of traditional phytoremediation techniques,the method of plant-microbe joint remediation has attracted much attention in recent years.Compared with single microorganisms,compound microorganisms can further promote plant growth and absorb heavy metals.There have been many studies on compound microorganism inoculants.In this study,we used the plant growth-promoting bacteria PGP5 and PGP6 obtained by the research group to prepare the composite microorganism PGP6+5,and quantitatively determined its ability to produce IAA and siderophores.The pot experiment was used to determine that the effect of compound bacteria on the accumulation of heavy metals and anti-oxidation of Solanum nigrum L..This study also carried out field experiments in combination with farmland of different types and different levels of heavy metal pollution to verify the effect of the compound microbial inoculants to enhance the extraction of heavy metals from plants and its suitability in different environments.This research provides a theoretical basis for the bioremediation of heavy metals extracted from plants by compound microorganisms,and also provides reference value for the field application of compound microorganism inoculants.The results of the study are as follows:Quantitative detection of the compound strain producing IAA,the result showed that the compound strain PGP6+5 had stronger IAA production capacity than the single strain,up to35.13 mg/L;the compound strain was quantitatively tested for iron carrier production,and the result showed that the compound strain PGP6+5 siderophores activity unit is 0.604;through pot experiment,it is found that the inoculation of the compound bacterial agent PGP6+5 can significantly increase the biomass and heavy metal accumulation of Solanum nigrum L.,and the effect is better than single bacterial agent.Compared with the untreated group,the dry weight of Solanum nigrum L.was increased by 59.12%;the dry weight of roots was increased by 35.50%;the accumulation of cadmium in the ground was increased by 37.71%;the accumulation of lead in the ground was increased by 56.70%.In addition,the compound bacterial agent PGP6+5 reduces the content of MDA,H₂O₂,O₂^-and proline,increases the content of GSH and the activity of antioxidant enzymes in Solanum nigrum L.to increase the tolerance of Solanum nigrum L.to heavy metals,and help Solanum nigrum L.absorb more cadmium.Under the field conditions in Huanggu Village,Zhuzhou,Hunan,compared with the untreated group,the plant biomass and the accumulation of Cd and Pb in the above-ground part of the plants treated with the inoculants of Linum usitatissimum L.,Tagetes erecta L.and Phytolacca americana L.increased significantly.In addition,the combination of Linum usitatissimum L.+compound bacterial agent PGP6+5 had the largest accumulation of heavy metals,the average accumulation of Cd and Pb in the shoots were 420.49μg/plant and 162.16μg/plant,and the extraction amount of Cd and Pb per mu was 3.36 g and 1.30 g,respectively,which increased by 78.25%and 66.47%respectively compared with the control group;under the field conditions in Tangshan,Nanjing,Jiangsu,compared with the untreated group,the plant biomass and the accumulation of Cd,Pb and Cu in the above-ground parts of the Linum usitatissimum L.,Cichorium intybus L.and Solanum nigrum L.treated with the inoculum were significantly increased,and the combination of Cichorium intybus L.+compound microbial agent PGP6+5 had the largest accumulation of heavy metals Pb and Cu in the shoots,the average accumulation of Pb and Cu in the shoots were 28.14μg/plant and 2653.00μg/plant,and the extraction amounts of Pb and Cu per mu were 225.12 mg and 21.22 g,respectively,which increased by 131.69%and 161.03%respectively compared with the control group;the accumulation of Cd in the shoots of the Cichorium intybus L.under the treatment of single inoculum PGP5 was the largest,the average Cd accumulation in the shoots was 33.23μg/plant,and the cadmium extraction per mu was 265.84 mg,which was an increase of 173.56%compared with the control group.It can be seen that the compound microbial inoculum enhanced plant extraction technology has suitability in different environments.Therefore,for the farmland contaminated by heavy metals in Huanggu Village,Zhuzhou,Hunan,a field remediation plan of Linum usitatissimum L.+compound inoculum PGP6+5 can be established;for farmland contaminated by heavy metals in Tangshan,Nanjing,Jiangsu,two field remediation plans of Cichorium intybus L.+compound inoculum PGP6+5 and Cichorium intybus L.+inoculant PGP5 can be established.