Study On Solanum Nigrum L. And Microbe Combined Remediation On Cd Contaminated Soil

Heavy metals are widely found in the environment, which originate from humanactivities in production, such as metal smelting, irrigation, and mining. The heavy metalnot only affects the soil environment, thus decreasing the yield and quality of the crops,but also deteriorates the water, even accumulates in the human body through the foodchains, which will endanger the health. Phytoremediation is a green，effective andeconomical choice of soil treatment，but it often has problems such as slow growth andlong repair period. Adding microbe can enhance the effect of phytoremediation, makeup for the deficiency of phytoremediation, and improve the efficiency ofphytoremediation. So plant-microbe combined remediation has a certain prospect ofapplication to ameliorate soil polluted by heavy metals. Pot experiments wereperformed to study the enhancement effects of microbe on the Cd absorption byhyperaccumulator Solanum nigrum L. The Cd-resistant rhizobacteria and endophyticwere isolated from the plant rhizosphere and Solanum nigrum L. from the district ofheavy meal pollution. The results showed:1. A kind of plant named S14, which could resist and accumulate Cd was selectedfrom nineteen plants, collected from gangue district of Da Bao Mountain in GuangdongProvince.The Cd absorption of S14was up to52.3mg/kg in natural pollution conditions.The ability of Cd resistance and accumulation was investigated by pot experiments inwhich Cd hyperaccumulator Solanum nigrum L. was as a control. The result showed theability of Cd resistance was poor in the early growth stage (15days), the growth of S14was obviously inhibited in the Cd concentration of10,30,60mg/kg; S14showed arobust ability of tolerance in the low concentration of Cd pollution (10mg/kg) at latergrowth stage (45days), in which root system was well developed and biomass wasconspicuously higher than the control; the Cd content in aboveground parts of S14wasreached44.38mg/kg at the the high concentration of Cd pollution environment (60mg/kg).2. Twenty-five Cd-resistant(100mg/L) strains were isolated from the root, stem,leaf of Solanum nigrum L. and the rhizosphere soil of gangue district of Da BaoMountain in Guangdong Province, including seventeen from the rhizosphere soil andeight from Solanum nigrum L., in which five strains showed a strong tolerance againstCd, up to400mg/L under laboratory conditions. Based on the phylogenetic analysis of the16S rRNA sequence, the Cd-resistant strains were mainly belonged to Bacillu,Pseudomonas, Enterobacter, Proteus, Klebsiella and Variovorax, especially Bacillu andProteus bacteria.3. Eight Cd-resistant strains were screened out by investigating the ability ofproducing ACC deaminase, IAA, oxalic acid, lactic acid and other organic acidscomprehensively. According to the morphological and physiological characteristics, andthe gene sequence of16S rRNA, the rhizobacteria TL3, DBS2and TL14(1) wereidentified as Proteus mirabilis, the five endophytic N1,N2,N4,DE2,DE5were Bacillussp., Enterobacter sp., Bacillus megaterium, Klebsiella Trevisan and Variovoraxparadoxus respectively.4. Then a consolidated remediation pot experiment was conducted to examine theenhancement effect of the two different kinds of strains on the growth and Cdabsorption of Solanum nigrum L., inoculated with rhizobacteria TL3, DBS2andendophytic N1, N2, N4of different groups in the Solanum nigrum L. land. The testindicated both rhizobacteria and endophytic could promote plant growth markedly, andstrengthen the Cd absorption from soil of Solanum nigrum L., and the groups withmixed strains were significantly better than the single strain groups. The Cd contents inroot of Solanum nigrum L. land treated with strainTL3,DBS2and both strains increasedby17.2%、85.6%and130.1%respectively, compared with the control. The amount ofCd uptake of four groups treated with strains N1+N2, N2+N4, N1+N4, N1+N2+N4inthe aboveground parts and underground parts were50%higher than thecontrol,especially the group of N1+N2+N4. In the Solanum nigrum L. land treated withstrains N1+N2+N4, the Cd content of aboveground parts and underground partsincreased by109.83%and83.01%respectively, and the amount of Cd uptake in leaf,stem and root respectively increased by135.30%,79.87%and83%than the control.5. Three strains rhizobacteria TL14(1) and endophytic DE2, DE5weresimultaneously inoculated in the Solanum nigrum L. land in different groups in potexperiment, dicussing the joint effect of the two kinds of strains on Solanum nigrum L.growth and its Cd absorption. The results were as follows: the promotion of Solanumnigrum L. growth was not obvious in the environment of non-Cd compared with thecontrol. But when the Cd concentration in soil increased to50and100mg/kg, thebiomass of the groups treated with mixed rhizobacteria-endophytic increasedsignificantly. The fresh-weight and dry-weight of rhizobacteria-endophytic group were higher than the control by64.81%,116.01%and64.81%,116.01%respectivelycompared with the group of single strain.The groups of mixed rhizobacteria-endophyticwere significantly better than the single strain groups in the amount of Cd uptake withlow Cd content (50mg/kg).When the Cd content increased to100mg/kg, the groupsthat were inoculated with single rhizobacteria and single endophytic were better than themixed groups.