| Phytoremediation is a hot topic in the field of soil heavy metal pollution remediation,due to its low cost and environmental protection.Low molecular weight acid can improve the biological availability of heavy metals in soil,and rhizosphere probiotics can affect the physiological characteristics of plant growth and heavy metal absorption in many ways.However,most reports are based on the study of phytoremediation efficiency of chelating agents or single interrhizal microorganisms,and few reports have been published on the combination of chelating agents and rhizosphere promoters to strengthen phytoremediation of heavy metals in soil.At the beginning of this study,8 organic and inorganic activators were selected to explore the activation rules and effects of activators on cadmium,lead and zinc in soil,so as to screen out the effect of low molecular weight acid activators with good effect and environmental protection,and the effects of low molecular weight acid on seed germination of Chinese cabbage were studied.Taking gramineous plants as the research object,the general rule of cadmium,lead and zinc absorption by plants was explored,and the adding time of chelating agents was mastered.Through pot experiment,the research between low molecular weight acid and Streptomyces Pactum Act12 on plant physiological and biochemical in heavy metals soil,the influence of accumulating Cd,Pb and Zn,meanwhile discusses the change of rhizosphere soil,aim to put forward a kind of high-efficiency,low-cost,environmentally-friendly repair methods of heavy metal pollution.The main findings are as follows:1. Among all the tested activators,the activation effects of Cd,Pb and Zn in soil were successively amino polycarboxylic acid chelating agents（EDTA,DTPA）>low molecular weight acid chelating agents（citric acid,acetic acid,etc.）and inorganic activator（HCl,Na Cl）,meanwhile the activation effects were enhanced with the increase of activator concentration.The activation effects of EDTA and DTPA on heavy metals in soil were the best,followed by Na Cl,citric acid and acetic acid.In comparison,oxalic acid has the worst activation effect.The activation rule of chelating agents is a three-day minimum inflection point.2. The effects of Cd,Pb,Zn,citric acid,acetic acid and DTPA on seed germination of Chinese cabbage were studied.The results showed:（1）the mixture of heavy metals Cd,Pb and Zn with low concentration promoted seed germination and growth.（2）the germination index（GI）of DTPA treatment was 1.36～17.25%,which was more toxic to seeds than citric acid and acetic acid.（3）under the mixed treatment of chelating agent and heavy metal,GI<50%,and with the increase of concentration of heavy metal or chelating agent,The GI decreases,the toxicity is greater.3. Through sand culture test,the study on the variation law of Cd,Pb and Zn absorption in wheat found:（1）30 days ago,the absorption rate of Cd,Pb and Zn in wheat was relatively large,and then the rate basically tended to be flat.（2）when Cd≤0.05 mg·L-1,Pb≤1 mg·L-1and Zn≤10 mg·L-1,treated with Hoagland solution containing a single heavy metal,the absorption amount and absorption rate of heavy metal in wheat increased significantly with the increase of the heavy metal concentration.（3）under the treatment of Hoagland solution with complex heavy metals,except for Pb,the absorption of Cd and Zn in wheat increased with the increase of heavy metal ion concentration,just as the single treatment.4. The effects of chelating agent and Act12 on growth and antioxidant properties of maize were studied.The results showed:（1）compared with the control,Streptomyces Pactum Act12,citric acid,and acetic acid could promote the growth of corn,and the dry weight and plant height of corn increased first and then decreased with the increase of Act12content,while the treatment of adding DTPA decreased significantly all the time（P<0.05）.（2）Act12 can effectively increase the activity of SOD,CAT and POD of antioxidant enzymes in maize leaves,and enhance the tolerance of maize to chelating agents and heavy metals.（3）Act12 reduced MDA content in maize leaves,and MDA tended to decrease first and then increase as the amount of Act12 increased in the treatment with chelating agent.5. The effects of chelating agents and Act12 on basic physicochemical properties of potting soil were investigated.It was found:（1）when chelating agents（citric acid,acetic acid,DTPA）and Act12 were applied to the soil of maize cultivation alone or in combination,the p H was reduced.With or without chelating agent,the p H decreased with the increase of Act12.The p H value treated with citric acid and 2.5 g·kg-1Act12 was the smallest,decreasing by 0.44 units compared with control.（2）The single and combined treatment of Act12 and small organic acids reduced soil organic matter and slightly increased DOC,while the combined treatment of Act12 and DTPA significantly increased organic matter and DOC（P<0.05）.6. The effects of chelating agents and Act12 on heavy metal accumulation and rhizosphere soil of maize were studied.The results showed:（1）under the treatments of 1.5g·kg-1Act12,the activation rates of citric acid,acetic acid and DTPA on rhizosperm Cd,Pb,Zn respectively increased by 73.4%～82.5%,89.4%～101.7%,and 58.9%～223.7%,reaching the maximum under all Act12 treatments.Among all treatments,DTPA had the best activation effect on heavy metals,followed by citric acid.（2）compared with the control,the concentration of Cd,Pb and Zn in corn was significantly increased by the combined application of chelating agent and Act12（P<0.05）,and the accumulation of Pb and Zn in corn was the largest under the treatment of 1.5 g·kg-1Act12 and chelating agent,the accumulation of Cd was the largest under the treatment of 2.5 g·kg-1Act12 and chelating agent.（3）The combined treatment of citric acid,acetic acid,DTPA and Act12,respectively,significantly increased the activities of urease,alkaline phosphatase and sucrase,while inhibited or activated the activities of dehydrogenase.Thus,compared with DTPA,low molecular weight acids（citric acid and acetic acid）have the characteristics of easy degradation,low toxicity and high activation efficiency.Meanwhile,they combine with Act12,which promotes growth,to make up for the traditional phytoremediation which is time-consuming and inefficient. |
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