| Phytoremediation was considered to be a low cost and environmental friendly technology for remediation of heavy-metal-contaminated soil.Rhizobacteria could affect plant growth and heavy metal uptake by a variety of ways in contaminated soil,thus influence the efficiency of phytoremediation of heavy metals in the soil.The present researches were mainly focused on bacteria and fungi,and few studies have focused on multifunctional Streptomyces sp in phytoremediation of heavy metal contaminated.In this paper,a multifunctional actinomycete Act12(Streptomyces pactum)with strong promoting effects was used to determine the resistance to lead and cadmium,drought tolerance and growth-promoting characteristics.Pot experiments were carried out to study the effects of the bacteria on plant growth,lead and cadmium uptake in the semi-arid and contaminated soil,to further investigate plant physiological and biochemical characteristics and effects of rhizosphere soil by actinomycetes in lead and cadmium stressed soil,and to explore phytoremediation effects and the strengthening mechanisms.In addition,further study was carried out to explore the growth effects and phytoremediation efficiency in ryegrass with addition organic fertilizer and microbial inoculum in Pb-contaminated soil.The aim was to provide theoretical and experimental basis for the study of fertilizer-bacteria combined in enhancing phytoremediation of heavy-metal-polluted soil.The main results are as follows:1.The test Streptomyces pactum had strong resistance to Pb and Cd,with the minimum inhibitory concentration of 1200 mg·kg-1 and 120 mg·kg-1,respectively.The strain had strong drought tolerance which can grow in the penetration of-0.73 MPa.It also had growth-promoting properties,with production of IAA and siderophore,high activity of ACC deaminase,also with phosphate solubilization.2.The ryegrass growth and tolerance under semi-arid water-deficit and lead stress(0-1000 mg·kg-1)were studied by Streptomyces pactum inoculation.The results showed that(1)the tested bacteria had a positive effects on ryegrass growth under semi-arid water-deficit and lead stress.(2)Bacteria inoculation can enhance plant tolerance under semi-arid water-deficit and lead stress.The inoculation increased the leaf chlorophyll content,antioxidant enzyme of CAT,SOD and POD activities,the GSH content and root activity were respectively increased by 2.0%-49.9% and 30.9%-166.8%.While root and leaf MDA content were decreased.Especially in the high concentration of Pb(500-1000 mg kg-1),MDA content was significantly reduced(P<0.05).3.Lead accumulation in ryegrass and its rhizosphere soil under semi-arid water-deficit and lead stress were studied by Streptomyces pactum inoculation.The results showed that(1)The inoculation significantly increased the Pb concentration in shoot and root by 12.4%-199.3% and 9.4%-44.0%,respectively.The Pb uptake per plant were respectively increased by 18.5%-213.8% and 69.6%-249.3%(P<0.05)in 200-1000 mg kg-1 Pb of soil,compared to the control.(2)The inoculation significantly increased the value of TF,shoot BCF androot BCF.And the root Pb accumulation(200-1000 mg·kg-1 Pb)reached the criteria of hyper-accumulator.(3)The teat strain can colonized well and became dominant actinomycetes species in ryegrass rhizosphere soil,with 0.8%-4.1% of colonization rate.Inoculation treatmeats increased the numbers of bacteria and fungi,thus changed soil microbial communities in ryegrass rhizosphere flora.(4)The inoculation treatments had a little effects on the rhizosphere soil catalase,but respectively increased soil phosphatase and sucrase activities.(5)The inoculation increased the content of bioavailability Pb by 8.4%-37.2% in the rhizosphere soil,but in non-rhizosphere soil the content of bioavailability Pb was reduced by 8.4%-14.1%.4.The plant growth and tolerance of Amaranthus hypochondriacus under semi-arid water-deficit and cadmium stress(0-100 mg·kg-1)were studied by Streptomyces pactum inoculation.The results showed that(1)The bacteria exhibited high plant-growth-promoting function in Amaranthus hypochondriacus.Plant height,root length and dry weight were increased by the tested bacteria inoculation in Cd-contamination soil.(2)The strain increased leaf chlorophyll and GSH content,antioxidant enzyme activities in leaves and root activity,but decreased the content of MDA in leaves by 15.1%-27.7%,and thus enhanced the Cd-tolerance of Amaranthus.5.Cadmium accumulation in Amaranthus and its rhizosphere soil under semi-arid water-deficit and lead stress were studied by Streptomyces pactum inoculation.The results showed that(1)The inoculation increased biological enrichment and remediation efficiency of Cd.Compared with the control treatment,plant Cd concentrations were increased in 10-100 mg kg-1 soil Cd(root 8.7%-33.9%;shoot 53.2%-102.1%),and the total Cd-uptake were significantly increased(root 19.9%-95.3%;shoot 110.6%-170.1%).The TF value(1.04-1.57)with the test strain was greater than 1.0 by the threshold of hyperaccumulator plants,and increase by 14.2%-75% compared with the control.Enrichment coefficient inroot and shoot were almost greater than 1.(2)The inoculation significantly increased the rhizosphere soil bacteria and actinomycetes,but reduced the amount of fungus,and thus changed soil microbial flora.The bacteria can colonized well with 1.1%-2.9% colonization rate and became dominant actinomycetes species.(3)The inoculation increased the rhizosphere soil neutral phosphatase,urease and invertase activity,but decreased catalase activity to a certain extent.(4)The bacteria inoculation increased the content of bioavailability Cd and decreased soil residue Cd in the rhizosphere soil.6.The plant growth and Pb-tolerance of ryegrass with the combined application of test bacteria and fertilizer under lead stress were studied.Results showed that(1)Under lead stress,strain or/and manure fertilizer could promote the growth of ryegrass.(2)Under lead stress,strain or/and manure fertilizer can enhance plant tolerance to Pb.The chlorophyll content,antioxidant enzymes of SOD,CAT,POD activity,and GSH were higher than other treatments,with significant increase compared with the control.The MDA contents were significantly decreased.7.The effects on Pb accumulation in ryegrass and its rhizosphere soil under lead stress were studied in application of manure and bacteria.The results showed that(1)Shoot Pb concentration and accumulation in bacteria and fertilizer treatments were significantly increased by 554.8% and 1360.1% in ryegrass under Pb stress,compared with the control treatment.And with maximum growth rate of 193% and 412.2% compared with the single bacteria treatment;Single fertilization reduced shoot Pb concentration and uptake,but with no significant difference compared to control treatment.(2)Organic fertilizer decreased the enrichment coefficient and transfer factor of Pb by ryegrass,but with 816.3% and 557.8% increase rate in Bacteria+Fertilizer treatment compared with control,with 483.9% and 193.5% increase rate in Bacteria+Fertilizer treatment compared with single bacteria treatment.The train innoculation significantly increased the root Pb concentration.Root BCF value was greater than 1,but root BCF were significantly reduced by 33.5% and 28.2% in the Fertilizer treatment and Bacteria+Fertilizer treatment,compared with the control.It was obvious observed that organic fertilizer had negative effects on the root Pb enrichment.(3)Compared with the control,strain or/and manure fertilizer could significantly increase the quantities of soil microorganisms in ryegrass rhizosphere,and thus caused changes in rhizosphere soil microbial community composition in Bacteria+Fertilizer treatment.The number of tested strains in Bacteria+Fertilizer treatment was approximately 3 times of in single bacteria treatment,and accounting for about 30% of actinomycetes.(4)Strain or/and manure fertilizer could significantly increase soil enzyme activity.However,fertilization decreased the catalase activity.(5)Soil rhizosphere pH were decreased in Fertilizer and Bacteria+Fertilizer treatments,but bioavailability Pb in the rhizosphere soil were significantly increased in Bacteria treatment and Bacteria+Fertilizer treatment(P<0.05).Bioavailability Pb content in Fertilizer treatment was significantly decreased by 20.0%,compared with the control treatment.In short,the actinomycetes exhibited great potential and application value in enhancing phytoremediation of semi-arid soil heavy metal of lead and cadmium.The efficiency of phytoremediation in heavy metals can be further enhanced by the combination of fertilizer and bacteria. |
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