Screening Of Plant Growth-promoting Bacteria And Its Effects On Growth And Copper Accumulation Of Sorghum Sudanense Under Different Levels Of Copper Contamination

Remediation of mining wasteland is becoming an important research topic.Phytoremediation is considered as a less-cost,convenient operation and environment-friendly technology.In response to the global energy crisis,there has been a rapid expansion of bioenergy production.Energy plants can be used to remediate mining wasteland because of their strong adaptability.The biomass of energy plants determines the efficiency of phytoremediation of heavy metal-contaminated soils.Bacteria can promote plant growth and increase heavy metal bioavailability and affect heavy metal accumulation of plants by many approaches thus facilitate phytoremediation.Therefore,it is important for investigating the effects of heavy metals on the growth and Cu uptake of Sorghum sudanense,screening the heavy metal-resistant and plant growth-promoting bacteria,and evaluating the bacteria-enhanced phytoremediation of Cu-contaminated soils.The energy plants Sorghum sudanense has many advantages,such as wild adaptation,fast growth,great biomass,flourish roots and good quality.In this experiment,the effects of different levels of Cu contamination on the growth and Cu accumulation of Sorghum sudanense were investigated.Higher level of Cu contamination decreased the growth of Sorghum sudanense.In the presence of low level(LS)of Cu contamination,the total Cu uptake of Sorghum sudanense reached 164 μg,while in the presence of high level(HS)of Cu contamination,the total Cu uptake of Sorghum sudanense reached to 3811 μg.Polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE)and molecular cloning were used to explore the effect of different levels of Cu pollution on the microbial community in rhizosphere and bulk soils.The high level of Cu pollution affected the bacterial communities.However,the ratios of 1-aminocyclopropane-l-carboxylic acid(ACC)deaminase-,indole-3-acetic acid(IAA)-,arginine decarboxylase(ADC)-,and siderophore-producing bacteria is higher in low level of Cu contamination than in moderate and high level of Cu contamination.In this experiment,six Cu-resistant and ACC deaminase-producing bacteria were isolated from the rhizosphere soils,bulk soils and roots of Sorghum sudanense.The bacteria showed the other plant growth-promoting characteristics such as the production of IAA and siderophores and mineral phosphate solubilization and ADC.The bacteria also have the resistance to heavy metals and antibiotics.The strains K1-6,N3G-5,K3-2 and K3-9,H1F-7,and N2G-9 were identified as Rhizobium,Microbacterium,Enterobacter,Bacillus and Acinetobacter respectively based on 16S rRNA gene sequences analyses.We selected Sorghum sudanense for the phytoremediation in water agar experiment to investigate the effect of Cu-resistant plant growth promoting bacteria on the growth of seedlings biomass and Cu accumulation.The results indicated that all six strains increased the biomass and Cu accumulation of Sorghum sudanense in Cu stress.K3-2 was selected as test strain.Sorghum sudanense was grown for 70 days in dfferent levels of Cu contamination(LS、MS、HS)and different bacteria inoculation(D-K3-2:dead-bacteria inoculation L-K3-2:live-bacteria inoculation)was used to investigate the effects of the strain on the growth and Cu uptake of Sorghum sudanense.The root dry weight of Sorghum sudanense in LS、MS、HS conditions in the presence of strain K3-2 was significantly increased by 14.69%,21.45%and 27.96%,respectively(p<0.05),compared with the dead-bacteria inoculation.The above-ground tissue dry weight was significantly increased by 21.2%,respectively(p<0.05),compared with the dead-bacteria inoculation.To some extent,inoculation of strain K3-3 decreased rhizosphere and bulk soil pH and significantly increased soil water extractable Cu(p<0.05)in HS.Compared to the dead-bacteria inoculation,inoculation with strain K3-2 increased Cu absorption and transportation in Sorghum sudanense in LS,MS,HS.The total Cu uptake in the roots of Sorghum sudanense in LS,MS,HS inoculated with strain K3-2 was significantly increased by 3.64%,73.71%and 58.17%,The total Cu uptake in the above-ground tissues of Sorghum sudanense in LS,MS,HS inoculated with strain K3-2 was significantly increased,compared with the dead-bacteria inoculation.The results indicated that Cu-resistant and plant growth-promoting endophytic bacterium K3-2 can greatly promote the growth of Sorghum sudanense and increase the ability of Cu uptake by Sorghum sudanense from the Cu-contaminated soils.