The Plant Growth-promoting And Molecular Ecological Effects Of Plant Growth-promoting Bacteria In Heavy Metal-contaminated Agriculture Soil

Plant growth-promoting bacteria(PGPB)can enhance the phytoremediation efficiency through promoting the growth and improving the heavy metal-resistance of plants.Due to the complexity of soil environment and adaptability of PGPB,it is urgent to find and utilize the dominant native PGPB with multiple resistance in heavy metal-contamination soil.In addition,the current studies on the application of PGPB to strengthen the heavy metal phytoremediation are mainly focus on the evaluation of the restoration effect.Few studies have paid attention to the environmental behavior and ecological effects of PGPB in soil.The purpose of this study was: 1)to isolate and identify a group of indigenous PGPB with multiple heavy metal resistance from heavy metal contaminated farmland located in Le'an River basin,Poyang Lake,Jiangxi Province;2)to study the effect of PGPB on plant growth and heavy metal remediation in situ;3)to evaluate the influence and ecological effect of applying PGPB on indigenous microbial communities in heavy metal contaminated soil.(1)A total of 34 strains with the resistance of Cu(100mg/L),Pb(1200mg/L),Zn(3200mg/L),As(800mg/L)were isolated from heavy metal contaminated farmland.There were 10 isolates with relatively high PGP activities were selected and identified to belong to the genera Burkholderia(6),Cupriavidus(2),Pseudomonas(1)and Ralstonia(1).Among them,Pseudomonas monteilii strain S2-3,Burkholderia anthina strain S9-17,Burkholderia latens strain S7-22 possessed the highest ability of indoleacetic acid production,siderophore production and phosphate solubilization,respectively.Burkholderia anthina strain S6-1 had the best performance of 1-aminocyclopropane-1-carboxylic acid deaminase and ammonia production.Besides,all isolates showed good heavy metal resistance,antibiotic resistance,acid and alkali resistance and salt tolerance.(2)Compared with non-inoculated plants,inoculation of P.monteilii strain S2-3and B.anthina strain S6-1 significantly increased the shoot length,fresh and dry root weight and N uptake of sorghum(Sorghum bicolor L.).While,there was no significant difference in proline content,malondialdehyde content,soluble protein content,CAT activities,POD activities and SOD activities.Inoculation of strain S2-3and S6-1 significantly increased the number of culturable bacteria and total nitrogen content in soil compared to the control treatment.Besides,the presence of S6-1significantly increased Pb content and translocation factor of Zn of sorghum.the Cu content and Zn content in the aerial parts of the sorghum subsoil in The presence S2-3 significantly increased the Cu content and Zn content in the aerial parts of sorghum compared to the control treatments.The translocation factor,bio-accumulation factor and remediation factor of Zn and remediation factor of Cu for sorghum were increased significantly in the presence of strain S2-3.(3)The application of PGPB in heavy metal-contaminated soil did not significantly affect the soil physic-chemical properties and heavy metal content.The soil physic-chemical properties,bacterial community structure and function of each inoculated treatment showed a consistent trend with sampling time.The 16 S r RNA gene copies of soil bacteria and the proportion of PGPB were gradually decreased with sampling time.The treatments were sorted by the number of edges derived from Co-occurrence network analysis,which were UW4,S6-1,S2-3,17400 and CK.The inoculation of strains P.monteilii strain S2-3,B.anthina strain S6-1 and Pseudomonas putida UW4 have enhanced the interactions between main modules and increased the number of connectors of soil bacterial networks.In summary,the indigenous strain P.monteilii strain S2-3 and B.anthina strain S6-1 possessed both relatively high PGP activities and good resistant characteristics in overall comparison.Simility,the other strains also performed favorable plant growth-promoting properties and resistance characteristics.The indigenous P.monteilii strain S2-3 and B.anthina strain S6-1 show fairish effects on sorghum growth and heavy metal phytoremediation,and may be used as candidates of PGPB with multiple resistances in heavy metal phytoremediation in the future.Moreover,The application of PGPB in heavy metal-contaminated soil did not significantly affect the soil physic-chemical properties,bacterial community structure and function,indicating that the application of PGPB did not lead to ecological risks probably.Co-occurrence network analysis showed that PGPB with good plant growth-promoting characteristics increased the interactions between major species of bacterial communities and made the links between species more compact,which is beneficial to improved the stability and metabolism of microbial community.In this study,for the first time,a group of indigenous PGPBs with multiple heavy metals and other resistance characteristics were isolated and screened from heavy metal-contaminated farmland located in Le'an River basin,Poyang Lake,Jiangxi Province.A number of valuable indigenous PGPB resources have been provided for the practical application of plant-microbial remediation technology.From the perspective of soil physic-chemical properties,heavy metal content,microbial community structure and function and the interactions between species,to explore the effects of applying PGPB on the indigenous microbial communities and their ecological effects.Which will provide a more comprehensive scientific basis for the practical application of potential PGPB to improved the heavy metal phytoremediation.