Effects Of CA And EDTA On The Growth Of Chlorophytum Comosum In Copper-contaminated Soil

With predatory exploitation of copper mines, discharge of industrial wastewater and long-term utilization of copper-contaminated fertilizers, the situation ofcopper pollution has been very serious in some areas of our country. The copper insoil has brought an adverse impact to the growth and yield of crops, while theaccumulated copper in plants has constituted a threat to the health of higher animalsand human beings through food chain. Therefore, the control to copper pollution insoil is so urgent that to find the control path of soil pollution is imminent.After years of constant exploration, the phytoremediation of contaminated soil,due to its low cost, significant effect and no secondary pollution, provides a greenway to solve the problem of heavy metal pollution in soil. As a new technology ofsoil-pollution treatment, chelate-induced phytoremediation is attracting moreattention and has become a focus in the field of environmental science.Chlorophytum comosum in Liliaceae, is a common kind of ornamental plants,which has strong adaptability to environment and patience to a variety of heavymetals. In this study, we took C. comosum as the experimental plant to repaircopper-contaminated soil, meanwhile took citric acid (CA) andethylenediaminetetraacetic acid (EDTA) as chelating agents of copper in soil.Through the experimental analysis of relevant indicators, we discussed the functionof C. comosum in repairing copper-polluted soil and the effects of CA and EDTAon the growth of C.comosum in copper-contaminated soil. Provided theoreticalfoundation and scientific basis for the application of CA and EDTA inphytoremediation of soil. The main conclusions are as follows:1. C. comosum had a certain enrichment of copper, and it could effectivelyreduce the content of copper in soil. When the copper treatment was above500mg·kg-1, C. comosum died. Cultivating C. comosum could promote theenzymatic activities of soil in copper-contaminated soil and could also stabilize andameliorate the basically physical and chemical properties of soil. 2. The copper enrichment in roots of C. comosum was higher. High levels ofcopper stress would promote copper to transfer from roots to aboveground parts.Because of the distribution of copper in C. comosum, the length and fresh weight ofroots was inhibited significantly with the rise of copper concentration in soil, butthe heigh and fresh weight of aboveground parts responded copper stress byfluctuation. The copper treatment under400mg·kg-1would not affect thephysiological indexes of C. comosum greatly. The sensitivity of antioxidantenzymes in C. comosum to copper was as follows: SOD>POD>CAT. Lowconcentration of copper could improve the activities of CAT and POD in a certainextent to help C. comosum resist oxidative damage from reactive oxygen. However,high levels of copper stress would break the dynamic balance of reactive oxygen,destroy the structure and function of antioxidant enzymes and inhibit the enzymaticactivities of C. comosum.3. The activation of copper by CA and EDTA achieved its maximum at theconcentration of5mmol·L-1, and the effect of CA was stronger. High levels ofchelating agents would form macromolecular chelates with metal to reduce thebiological effectiveness of copper in soil. The sensitive degree of enzyme incopper-contaminated soil to CA and EDTA was as follows: phosphatase and ureasewas the highest, catalase were the second, and invertase was the lowest. In contrast,the promoting effect of EDTA on activities of catalase and phosphatase was better,while CA was more effective in promoting the activitiy of urease.4. The relationship between the influences of CA and EDTA on copperenrichment of C. comosum and the activation of copper in soil by them weresignificantly positive correlation. CA could effectively improve the copperabsorption of C. comosum, and the effect was most obvious at the concentration of5mmol·L-1. CA might have a certain ability to promote the growth of C. comosumby itself, but its improving effect on copper enrichment indirectly inhibited themorphology indexes and biomass of C. comosum. The effect of EDTA on theenrichment and growth of C. comosum was weak, but it was significant on POD ofC. comosum.5. CA and EDTA might combine with Cu2+at the same time, therefore formmacromolecules chelates which was difficult for plants to absorb. It led to the decline of available copper in soil, and inhibited the activation effect of CA andEDTA. The interaction between CA and EDTA might make a further promotion onthe activity of phosphatase. But with the intervention of EDTA, the regulation ofCA on the activity of urease would get a certain inhibition.6. The mixed solution of CA and EDTA could promote the copper absorptionof C. comosum in a certain extent. Under the influences of CA and EDTA, thelength of root system was maintained steady basically, but the biomass ofC.comosum was obviously inhibited. The sensitivity of antioxidant enzymes ofC.comosum to the mixed chelating agents was SOD>POD>CAT. SOD wasinhibited, POD was improved and CAT was not affected at all. Almost all theindexes of C. comosum had linear relation with the concentration of EDTA inmixed chelating agents, but no linear relation existed between the indexes and CA.Evidently, the effect of EDTA on the growth of C. comosum incopper-contaminated soil was more direct.