| Heavy metal pollution in soil will not only damage plants,but also seriously do harm to human health.Traditional remediation methods are high cost and easy to cause secondary pollution to the environment.As an ecological friendly and safe remediation method,bioremediation has attracted much attention.The combined remediation of plantmicroorganisms method is a research hotspot.The application of efficient bacteria can often promote the growth of plants and the accumulation of heavy metals,and the subsequent application of microbial agents is a problem worthy of discussion.In this paper,two efficient bacteria PGP5(Bacillus sp.)and PGP41(Arthrobacter sp.)were applied to all experiments.Both of them can produce IAA,solubilize phosphate,fix nitrogen and have ACC deaminase activity to promote plants growth.Two plant growth promoting bacteria(PGPB)were applied in two parts of experiments:(1)under the condition of aseptic culture,PGPB interacted with Arabidopsis thaliana L.to explore the single growth promoting effect of PGPB on plants;(2)In order to explore the effect of PGPB interaction on Phytolacca americana L.about growth promotion,accumulation of heavy metals,and the changes of diversity and function of bacterial communities,the experiments use PGP5 and PGP41 co-cultured with plants in situ contaminated soil with heavy metals.Through these experiments,I hope to determine the effect and principle of excellent and efficient bacteria,and provide a theoretical basis for the practical application of the combined remediation of plant-microorganisms of heavy metal contaminated soil.The results are as follows:In order to explore the growth promoting effect of PGP5 and PGP41 on Arabidopsis thaliana L.,it was found that: when Arabidopsis thaliana L.was cultured on 1/2 MS solid medium,the addition of PGP5 and PGP41 made plants show obvious growth promoting effect at 3 days,specifically in shoot length,diameter,shoot fresh weight and root fresh weight.It also had significant growth promoting effect on treatments after 7 days and 15 days.Overall,the growth promoting effect of PGP41 is better than that of PGP5.A similar growthpromoting effect was observed in Arabidopsis thaliana L.cultured in aseptic vermiculite vegetative soil,and the effect of these two bacteria was better under soil culture conditions.After the single growth promoting effect of the bacteria has been confirmed,in order to explore the practical application prospect of PGPB,pot experiments treated with PGP5 and PGP41 were also carried out on the heavy metal in situ contaminated soil collected from Nanjing Qixia with the hyperaccumulators Phytolacca americana L..Through this experiment we can know better about the certain effects about promoting plants growth and promoting the accumulation of heavy metals.The results showed that after 30 days of PGPB treatments,the biomass of Phytolacca americana L.about the two groups increased significantly.After PGP5 treated,the shoot fresh weight of plants increased by 45.27%,and the root fresh weight increased by 47.27%.After PGP41 treated,the shoot fresh weight increased by 86.67% and the root fresh weight increased by 59.06%.After 60 days of PGPB treatments,the plant biomass was increased to some extent,but the growth promotion effect was not as good as that of 30 days.Plant samples of 60 days were decomposed to find the effect of PGP5 and PGP41 increasing the accumulation of plants’ heavy metal cadmium.Compared with control group,the total accumulation of PGP5 treatment’s root to cadmium increased by 180.81%,and PGP41 treatment’s results increased by 227.47%.The results of shoot total accumulation are also increased significantly.DAPI staining was used for root slices of Phytolacca americana L.and specific primers of PGP5 and PGP41 were used to amplify root DNA.It was found that both PGP5 and PGP41 could not colonize in Phytolacca americana L.,they could only act in rhizosphere soil.Using16 S r RNA gene sequencing technology and metagenomic sequencing technology to analyze the diversity and function of bacterial communities in the rhizosphere soil of Phytolacca americana L.for different days.It was found that the relative abundance of PGP5 was the highest at the beginning,while the relative abundance of PGP41 reached the peak after 3days after treatment.After 3 days of treatment,the rhizosphere soil bacterial community diversity of the two groups was the lowest,and at 15-30 days,there was no significant difference between the two groups and the initial soil bacterial communities’ diversity.Metagenomic data also indicated similar conclusions.After 3 days of inoculation,COG annotation,NR annotation and KEGG functional annotation were significantly different from those in the control group,while at 30 days,the results were similar among all groups.According to the results of KEGG function annotations,it is speculated that after the application of PGP5,plants can enhance the resistance to diseases,reduce the production of ROS and promote plant growth;after the application of PGP41,the rhizosphere microbial community could secrete more vitamins,gibberellin,melatonin,etc.,thus enhancing the resistance of plants to abiotic stress and promoting plant growth.The combination of physiological data and sequencing data can also be preliminarily inferred: 3 days after the treatment of PGP5 and PGP41,the diversity and function of the rhizosphere bacterial communities showed significant differences.At the same time,both of two PGPB can only almost exist in the soil for 7-15 days,but Phytolacca americana L.still has a growth-promoting effect after 30 days of treatments.So we can draw a conclusion that applying a bacterial agent every 15 days can maximize the growth-promoting effect.Taking into account the cost issue,applying the inoculum every 30 days can also maintain the growth-promoting and the accumulation of heavy metals effect of the treatments on plants to a greater extent. |
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