| Plant extraction technology has a great potential in repairing heavy metal contaminated soil.Yet it is so far difficult to quickly achieve the ideal expectations by using the plants alone due to its low efficiency to clean up the soil heavy metals.The efficiency of phytoremediation can be improved by associated methods such as adding activator,applying alternating current?AC?electric field and agronomic measures.In this paper,soil incubation test and pot experiments were used to study the efficiency and mechanism of the above three strengthening measures to improve the remediation of heavy metal cadmium?Cd?contaminated soil by willow?Salix sp.?.The main results were as follows:?1?Application of AC electric field treatment changed soil Cd speciation.The soil available Cd concentration increased significantly with the increase of electric field gradient,and it was the highest when treated with 1 V·cm-1.The application of electric field was beneficial to willow plant growth.0.5V·cm-11 treatment had the best promoting effect on root morphology index and promote plant photosynthesis.1 V·cm-11 treatment had the best promoting effect on plant height,leaf area and biomass of willow.The application of AC electric field promoted the purification efficiency of soil Cd by willow,but different voltage gradients had different effects on the absorption and accumulation of Cd in willow.The 0.5 V·cm-11 treatment increased Cd accumulation of willow due to increasing willow biomass,while the 1 V·cm-11 treatment increased Cd accumulation of willow was attributed to increasing willow biomass and promoting Cd uptake by the willow as well.The Cd accumulation in the shoots of plants treated with 0.5 V·cm-11 and 1 V·cm-11 were 15.2 and 21.8%higher than that of the control,respectively,and Cd purification rates of willow were 1.11 and 1.17 times of the control,respectively.?2?Incubation experiment showed that milk vetch?MV?,potassium humate?PH?and citric acid?CA?increased soil available Cd content,changed soil Cd speciation and increased the percentage of acid extractable Cd.All three activating agents were beneficial to the increase of willow leaf area and some part of root morphology index,but inhibited the photosynthesis of willow.Both MV and PH treatment promoted the purification efficiency of soil Cd by willow.The Cd accumulation in the shoots of plants treated with MV treatment and PH treatment were 68.68?p<0.05?and 40.19%higher than that of the control,respectively,and soil Cd purification rate by willow plants were 1.65 and 1.42 times of the control,respectively.?3?Mixed growth of willow with Sedum alfredii Hance treatment reduced soil pH,but it was conducive to the improvement of soil organic matter and available Cd content and the elongation of the willow plant height,the increase of leaf area,the biomass of willow plants.However,the willow leaf photosynthesis reduced with mixed treatment,and promoted the absorption and accumulation of Cd in soil by willow.The accumulation of Cd in the shoots and roots in willow plants growing the mixed treatment was higher than that of the single willow treatment,which was significantly increased by 2.10and 41.07%,respectively.In summary,the three intensification measures were conducive to the purification of soil cadmium by willow.The AC electric field treatment promoted the growth of willow and improved Cd accumulation of willow.Under the condition of 0.5 V·cm-1,the use of MV as the activator was most beneficial to the growth of willow and soil Cd purification by willow,and the mixed pattern of Sedum alfredii Hance and willow was more conducive to the growth of willow and soil Cd purification by willow. |
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