Study On Strengthening Measures And Effects Of Phytoremediation Of Cd-contaminated Farmland Soil

Heavy metal pollution of farmland soil has great potential harm to the safety of agricultural products and human health.Among the existing remediation measures for heavy metal pollution in soil,phytoremediation is an environmentally-friendly,economic and effective green remediation technology.In the process of phytoremediation,how to improve the efficiency and shorten the repair cycle is an important problem.There are two ways to improve the efficiency of phytoremediation:one is to improve the effectiveness of Cd in soil by appropriate agronomic measures to improve the accumulation of Cd in the upper part of the plant,and the other is to improve the aboveground biomass of phytoremediation plants by promoting the growth of plants.In this study,Cd-contaminated farmland soil in South China was taken as the object,by adding low molecular weight organic acids and other agronomic measures,the effect and mechanism of enhanced remediation of cloisonne inCd-contaminated farmland soil were studied.This study can provide a basis for the selection of strengthening measures to improve the restoration efficiency of Sedum plumbizincicola,The main results are as follows:（1）Study on the effects of low-molecular-weight organic acids strengthen on phytoremediation of Cd-contaminated farmland soil,the results of soil culture experiment showed that citric acid and tartaric acid could significantly reduce soil p H（p<0.05）.Compared with the control（pH 6.4）,the soil pH decreased by 0.22-2.45 units on the second day after adding organic acid,and the available Cd（p<0.05）,Fe and Mn in soil increased significantly;the change range of soil pH and the available state of metal increased with the increase of organic acid addition;the effect of citric acid on soil pH and metal available state was greater than tartaric acid（except Mn）.The pH of red yellow mud and purple soil decreased after adding citric acid for 4 days,and increased slightly after adding citric acid for 30 days;Except for Cd in red and yellow mud,the available state of soil metals in two kinds of soil（except for the available state of individual metals）extracted by three extractants（CaCl₂,HCl and DTPA）on the second day after adding citric acid for one time were increased,the available state of soil metals in two kinds of soil with citric acid added 5 times（except for the available state of individual metals）extracted by HCl,were reduced on the second day after adding citric acid and were increased on the eighth/tenth day after adding citric acid.（2）Study on the effects of low-molecular-weight organic acids strengthen on phytoremediation of Cd-contaminated farmland soil,The results of field experiments showed that when the amount of organic acid was 0.2 mol/m2,the way of adding organic acid had an important effect on the availability of Cd in soil and the accumulation of Cd in Sedum plumbizincicola.Compared with the control,the content of available Cd in soil and Cd concentration in 0-10 cm soil solution increased significantly in two days when organic acid was added at one time（p<0.05）;the content of available Cd in soil and Cd concentration in 0-20 cm soil solution increased significantly in 8/10 days when organic acid was added at five times（p<0.05）;and the effect of citric acid treatment was better than tartaric acid.The addition of organic acids had no significant effect on Cd concentration in 20-30 cm soil solution.The content of Cd in the upper part of the field was 45.57-53.11 mg/kg,Adding organic acid could slightly increase the Cd content in different parts of Sedum plumbizincicola,the effect of adding citric acid five times on the absorption and accumulation of Cd in the upper part of the field of Sedum plumbizincicola was better.In addition,adding organic acids could increase the biomass of Sedum chaperone by increasing root activity and reducing MDA（malondialdehyde）in stem and leaf.（3）The study on the effects of intercropped Sedum plumbizincicola and maize strengthen on phytoremediation of Cd-contaminated farmland soil showed that different planting patterns had important effects on Cd availability in 0-30 cm soil and Cd accumulation in Sedum plumbizincicola.The pH of 0-30 cm soil increased with the increase of soil depth,but the available Cd was opposite.Both monoculture with Sedum plumbizincicola or intercropped Sedum plumbizincicola and maize could reduce soil p H and significantly increase soil available Cd（0-15 cm）（p<0.05）.Compared with monoculture,Intercropped Sedum plumbizincicola and maize could increase the biomass of maize,but had little effect on the biomass of Sedum plumbizincicola.Intercropped Sedum plumbizincicola and maize could increase the available Cd of 0-5cm soil on the side of Sedum plumbizincicola and 0-30 cm soil on the side of maize,and increased the content of Cd in the upper part and the lower part of Sedum plumbizincicola（increased by 7.93%and 18.60%respectively）.but there was no significant effect on the content of Cd in all parts of maize.（4）The study on the effects of intercropping/organic acid combination strengthen on phytoremediation of Cd-contaminated farmland soil showed that when the organic acid content was 0.2 mol/m2,the effect of different citric acid adding methods and planting patterns on the remediation of Cd-contaminated farmland soil by Sedum plumbizincicola was different.Planting Sedum plumbizincicola and adding citric acid five times can improve the availability of Cd in soil by increasing acid soluble Cd and soil reducible Cd.Under the same planting mode,adding citric acid could increase the biomass and Cd accumulation in the upper part of the field（the effect of five times adding citric acid is better than that of one time adding citric acid）,and then significantly increase the Cd removal in the upper part of the field of the Sedum plumbizincicola（p<0.05）,but add citric acid had no significant effect on the biomass of corn.In the same way of adding citric acid,Intercropped Sedum plumbizincicola and maize can improve the biomass of corn,but it has no obvious effect on the biomass of the above ground.In addition,the effect of adding citric acid to the intercropping on increasing the Cd accumulation and removal in the upper part of the field was more obvious than that of the monoculture,and on the basis of the intercropping,adding citric acid five times,the Cd content in the root,stem and leaf of the Sedum plumbizincicola and the Cd removal in the upper part of the field of the Sedum plumbizincicola were the largest,which were 10.63 mg/kg,71.21 mg/kg and 19.33 respectively mg/m² has the best strengthening effect on the remediation of Cd-contaminated farmland soil.That is to say,based on the intercropped Sedum plumbizincicola and maize,adding citric acid for five times was selected to improve the efficiency of Sedum plumbizincicol restoration and realize the safe production of maize.