| At present, a large number of heavy metals entered soil in different ways due to thesewage irrigation, industrial waste as well as waste water emission from the smelting ofheavy metals. The heavy metals (such as Cd, Pb, As, Hg, Zn) with significant biologicaltoxic harm to human health seriously through the food chain. The Cd was known as “themost toxic one” since the characteristics of Cd were larger mobility, higher toxicity andwider contamination areas among them. In view of this, the remediation problem of Cdcontaminated soil had become increasingly active in the field of environmental science.Traditional physical-chemical remediation methods existed some shortcomings that thepollutant removal was not complete and secondary pollution was still present, sobioremediation technology became a well-recognized repair method. In this paper, inorder to solve the limitation of a single plant or microbial remediation, Effects ofdifferent inoculum concentrations of Bacillus mucilaginosus on Cd accumulation inBrassica juncea, available Cd content, pH, soil enzymes, organic acids in soil wereinvestigated using pot culture experiments. The impact factor of Bacillus mucilaginosusbetween the soil，plant roots and heavy metals were analyzed and discussed. Elaboratedthe Bacillus mucilaginosus played an important role in activation of soil cadmium andthe repair effect of plants from the angle of Brassica juncea enrichment effect. Wish toprovide test guidance for the bacteria to promote Brassica juncea enrichment soil Cd,and give a scientific basis and technical support for phytoremediation technology withmicroorganisms assisted in the heavy metals contaminated soil. The main findings wereas follows:(1) The effects of Bacillus mucilaginosus on Cd enrichment in Brassica juncea weresignificant by different inoculum concentrations. The enrichment factor of abovegroundbiomass and underground biomass were5.66and2.35, respectively. Soildecontamination rate was4.43%, which was higher than that of other treatmentssignificantly. Thus inoculum concentrations of Bacillus mucilaginosus had an importanteffect on auxiliary repair effect, and too high or too low inoculum content was notconducive to the activation of microorganisms in the rhizosphere in the process ofpromoting the extraction of Cd in soil. The2×1010cfu kg-1soil was screened as the bestconcentrations of vaccination in the test.(2) The inoculum concentrations of Bacillus mucilaginosus affected the removal of cadmium in soil significantly. In harvest, the amount of decline in Cd content in thetreated soils were9.3%,9.1%,20.9%,13.2%,2.8%,4.7%respectively. The inoculum of2×1010cfu kg-1soil was the largest decline (20.9%), which was2.25,2.29,1.58,7.51,4.44times than others. And when the concentration of inoculum was4×1010or5×1010cfu kg-1soil, the activation effect of Cd in the soil had not been obvious basically.(3) The Bacillus mucilaginosus influenced on the enzymes activities in soilsignificantly. With the extension of time, soil phosphatase activity monotonicallyincreasing, and the activity of urease, dehydrogenase and peroxide hydrogen showed atrend of first increase and then decrease. The activity of Hydrogen peroxide anddehydrogenase reached maximum value in about20days after the inoculum while theactivity of urease attained the highest point about30days after the inoculum. The activitiesof soil enzymes had a significant change over time by the micro-organisms. Cd content inthe soil of control group was negatively correlated with urease, phosphatase(p<0.05).There was a significantly negatively correlation between the content of cadmium andurease or phosphatase after treatment(p<0.01).(4) The Bacillus mucilaginosus could improve the biological effectiveness of heavymetal Cd significantly. Cd content of effective state in the control group (CK) had amonotone decreasing trend with plant growth, Cd content of effective state decreased32.93%and45.54%respectively in the rhizosphere and non rhizosphere soil. After dealingwith the microbial, Cd content of effective state increased gradually over time, Cd contentof effective state in rhizosphere and non-rhizosphere of treatment A increased by15.15%and31.73%at harvest, and at the same time it increased by36.54%and45.28%intreatment C, respectively. These may be due to the role of microbes in rhizosphere wasmore active, the interaction between strains and plant roots lead to the more apparentactivation of Cd in soil.(5) The Bacillus mucilaginosus could reduce the pH in soil effectively. The pH lowerrate in rhizosphere of treatment A and C were3.30,3.65times than control at harvest, andthe pH lower rate were respectively3.30and3.65times than control in non-rhizosphere.Strongly suggested that the soil pH could reduce greatly after microbial treatment, anddifferent concentration of bacteria brought about differences in reducing the degree of pH.There were significant or extremely significant negative linear relationship between Cdcontent of effective state and the pH in rhizosphere and non rhizosphere soil.(6) The Bacillus mucilaginosus affected types and contents of organic acids in soil. Thisexperiment analyzed several kinds of low molecular organic acids which wererepresentative in soil-plant system. The content of lactic acid was stable in differentsampling periods. The variation which was similar between malonic acid, malic acid andtartaric acid was increased gradually over time. The contents of oxalic acid, succinic acidand citric acid which were not detected in the control group improved significantly with the increase of liquid inoculant concentration. The results showed that the interactionsbetween Bacillus mucilaginosus and plant-roots in the rhizosphere had benefit to add thetypes and improve the contents of low molecular organic acids around the root systemobviously. |
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