Effects Of PGPR Enterobacter Sp.Zm-123 On Cadmium Polluted Soil Remediation And Growth Promotion And Toxicity Reduction For Rape

With the rapid development of society and the accelerated process of industrialization,modernization and urbanization,soil heavy metal pollution is increasingly serious.When heavy metals enter crops,they will endanger human health through the food chain.Plant growth-promoting rhizobacteria can improve plant growth and improve plant resistance,reduce its toxic effects on plants by immobilizing heavy metal in the soi1.In recent years,Spent mushroom substrate(SMS)has been studied as solid waste to applied to the improvement of contaminated soil.In this study,a PGPR Enterobacter sp.Zm-123 was isolated from the rape rhizosphere soil,and its growth-promoting properties were determined,and its heavy metal resistance and Cd²⁺adsorption capacity were analyzed.The rape was used for hydroponic experiment,sprayed the bacterial liquid on the roots,analyzed the mechanism of promoting and attenuating the growth of rape under Cd stress according results,and then combined Zm-123 with SMS to prepare solids in different ways.Analyzed and compared its effects on soil Cd form distribution,rape growth and edible Cd content through pot experiment,which provided a scientific basis for remediation of Cd contaminated soil and safe production of crops.The main findings were as follows:(1)Isolation and identification of the Cd-resistant PGPR.A Cd-resistant growth-promoting bacterium was screened from the rape rhizosphere,and identified as belonging to Enterobacter sp.Zm-123 by morphological,physiological,biochemical and 16S r DNA sequence analysis.(2)PGPR Zm-123 had good tolerance to heavy metal and plant growth-promoting properties.The minimum inhibition concentration(MIC)of Pb(II),Cd(II),zinc(II),Cr(?)and Cu(II)on Zm-123 was 600,200,200,400 and 100 mg·L^-1,maximum tolerable concentration(MTC)of Zm-123 was 1000,600,400,800 and 300 mg·L^-1,respectively.Zm-123 showed good growth-promoting ability with different Cd concentrations.The maximum yield of siderophore production was 82.34%,phosphorus solubilizing capability was 137.50 mg·L^-1and IAA was 28.30mg·L^-1,respectively.(3)PGPR Zm-123 had strong adsorption capacity for Cd²⁺.The adsorption capacity of Zm-123 for Cd²⁺changes with the Cd concentration of the solution.When the Cd concentration is5 mg·L^-1,the Cd concentration is only 0.91 mg·L^-1after 48 hours,and the adsorption rate was81.80%.When the Cd concentration increased to 25 mg·L^-1,the growth of strain Zm-123 was inhibited.After 48 hours,the Cd concentration in the culture was 15.98 mg·L^-1and adsorption rate was 36.08%.(4)PGPR Zm-123 effectively promoted growth and reduced toxicity for rape under hydroponic conditions.At Cd concentration of 0.5-5.0 mg·L^-1,Zm-123 inoculation significantly promoted(p<0.05)rape growth(9.47%-19.98%)and increased the chlorophyll content(7.60%-96.67%).The activity of antioxidant enzymes POD and CAT were increased.And MDA content was reduced by 11.80%-28.61%,Cd content in edible part was reduced by 11.13%-35.87%.The effect was the best at 0.5 mg·L^-1concentration,with Cd content in the edible part was 0.16mg·kg^-1.(5)The solid microbial agent of PGPR Zm-123 effectively promoted the remediation of Cd contaminated soil and the growth of rape.The pot experiment result showed that compared with the control group,the five treatment groups SMS treatment,Zm-123 treatment,PH treatment,BY treatment and SSF treatment significantly increased the soil p H,and effect of solid microbial agents prepared by semi-solid fermentation was the best,increasing by 0.40,0.60,and 0.79 units,respectively.Organic matter,available phosphorus and potassium,soil enzyme activity and microbial biomass carbon and nitrogen had been improved.At the same time,the five treatments significantly reduced the SE-Cd content in soil,the effect of SSF treatment was best(19.56%-21.94%).The results of correlation analysis showed that p H and CEC were significantly negatively correlated with SE-Cd,and p H was significantly positively correlated with OM-Cd and RES-Cd.The results of pot experiment showed that compared with CK,five treatment significantly increased rape biomass(p<0.05),the effect in SSF group was the best,increasing by 16.62%-27.19%.The chlorophyll content and CAT and POD activities in rape were increased,the content of MDA and proline were decreased.Besides,,the content of Cd in edible parts of rape was also significantly decreased,SSF group had the best effect,with the reduction rates of 49.06%,32.73%and 30.53%,respectively.