Effects Of EDDS On Growth And Cd Accumulation Of Miscanthus Sacchariflorus Under Cd Stress

Industrialization,urbanization and other human activities have directly generated a serious environmental problem nowadays.The natural purification rate of heavy metals is very slow,so they are easier to accumulate in the environment.Excessive heavy metals not only lead to lower yields and lower quality of agricultural products,more seriously,they would enter the body through the food chain and directly harm human health.Therefore,the treatment of heavy metal contaminated soil is imminent.Phytoremediation is a technique of using plants to remove pollutants from the environment.It has the advantages of lower cost,beautifying the environment,in-situ remediation,and no secondary pollution.Chelator-enhanced phytoremediation is considered as a suitable method to remediate heavy metal contaminated soil.In this study,we choose Miscanthus sacchariflorus as remediation plant,and EDDS was used as chelating agent for soil Cd.The effects of Cd stress(0,3,6 and 9mg·kg^-1)on the growth,Cd accumulation characteristics and soil enzyme activities of Miscanthus sacchariflorus were studied by pot experiments from seed germination and cultivation for 132 d.The effects of EDDS(0,1,3 and 5 mmol·kg^-1)on the growth and heavy metals accumulation of Miscanthus sacchariflorus were studied by slight Cd,Pb contamination pot experiments.The effects of different application methods of EDDS on the growth and Cd accumulation characteristics of Miscanthus sacchariflorus under Cd stress were studied by pot experiments.The major results were as follows:1.The tolerance index of Miscanthus sacchariflorus increased at first and then decreased with the increase of the amount of Cd.When the amount of Cd was no more than6 mg·kg^-1,Cd increased the dry weight of Miscanthus sacchariflorus.When the amount of Cd equal to 9 mg·kg^-1,Cd caused the inhibition of growth.With the increase of Cd concentration,the content of chlorophyll,MDA and soluble sugar in leaves increased firstly and then decreased,and the maximums appeared at 6 mg·kg^-1.While the carotenoid content of leaves decreased at beginning and then increased,and the minimum appeared at 6 mg·kg^-1.Three micronutrients?Cu,Zn and Fe?in root increased gradually.Cu and Fe concentrations in aboveground part decreased at first and then increased,however Zn concentration was consistently decreasing.Cd concentration of root and aboveground part rose gradually with increased Cd concentration and the distribution of Cd was higher in root than in aboveground part.The root bioconcentration factors?BCF?of Miscanthus sacchariflorus exceeded 1 in various Cd treatments,but the aboveground part BCF and translocation factors?TF?was less than 1.Cd accumulation of root increased at first and then decreased with the increase of Cd concerntration,however Cd accumulation of aboveground part increased all the time.Furthermore,root was the main part of Cd accumulation.Soil enzyme activities of the treatment groups had no significant differences compared with CK?P>0.05?,Soil urease activity was promoted by Cd concentrations of 6 and 9mg·kg^-1,meanwhile,soil catalase activity was inhibited.Overall,the enzyme activities of urease and catalase in rhizosphere were high than those in non-rhizosphere.2.On the whole,there were no significant differences between the control and different treatments in photosynthetic pigments contents,plant heights and dry biomasses.In Cd contamination group,Cd concentration of aboveground and underground parts increased at first and then decreased in response to the increased EDDS concentrations,they reached the maximum values at EDDS 1 mmol·kg^-1.Cd translocation factors increased all the time,all of them were significantly higher than the control.Total Cd accumulation increased at first and then decreased,the maximum appeared at 3 mmol·kg^-1,which was 44.2%higher than the control.Translocation amount factors of different EDDS treatment were significantly higher than the control,and the maximum appeared at 5 mmol·kg^-1.Remediation efficiency of Cd contaminated soils met the maximum at 3 mmol·kg^-1,and 44.2%higher than the control.In Pb contamination group,the Pb concentrations and bioconcentration factors of aboveground part met the relatively higher value at 5 mmol·kg^-1,but there was no significant difference compared with control?P>0.05?.Pb concentrations and bioconcentration factors of underground part reached the peak value at 5 mmol·kg^-1,which were 37.5%and 35.3%higher than the control?P<0.05?.Aboveground,underground and total Pb accumulation decreased at first and then increased,the maximums appeared at 5 mmol·kg^-1 and 9.4%,56.7%and 46.6%higher than the control,but there were no significant difference?P>0.05?.Remediation efficiency of Pb contaminated soils decreased at first and then increased,the maximum appeared at5 mmol·kg^-1 and was 45.2%higher than the control?P>0.05?.3.All of the Miscanthus sacchariflorus seedlings exhibited toxicity symptom.Furthermore,a part of seedlings were dead in 4 and 8 mmol·kg^-1 EDDS treatment groups and the death rate were 7.04%⁸.93%and 41.14%⁶7.46%,respectively.The root length,plant height,root dry weight,shoot dry weight of Miscanthus sacchariflorus seedlings were consistently decreasing in groups of EDDS one-time application.In EDDS separation application groups,the growth status of seedlings were five times>ten times>one-time in total.In addition,the best theoretical times were 6⁷.In this study,all of EDDS treatments could enhance the Cd concentration of Miscanthus sacchariflorus in total.In 1 mg·kg^-1 Cd stress,1 mmol·kg^-1 EDDS treatment have the better strengthening effect.In 3 mg·kg^-1 Cd stress,2 mmol·kg^-1EDDS is the preference.4 and 8 mmol·kg^-1 EDDS were the better choice in 9 mg·kg^-1Cd stress.Compared with EDDS one-time application,EDDS separation application could not promote the the Cd concentration of Miscanthus sacchariflorus obviously.Cd accumulation of EDDS treatments of 1 mmol·kg^-1,2 mmol·kg^-1 in five times and 2mmol·kg^-1 in ten times were higher than CK.Cd accumulation of 2 mmol·kg^-1 in five times group were highest among all treatments.In addition,separation application of EDDS would promote the Cd accumulation of Miscanthus sacchariflorus compared with one-time application.