| Heavy metal pollution is becoming more and more serious in China,especially cadmium.There are many reports on Cd contaminated soil remediation in farmland,but there are few studies on Cd contaminated soil of traditional Chinese medicine.As a traditional Chinese herbal medicine in China,Anemarrhena asphodeloides and Leonurus japonicus are widely used.It has been pointed out that these two medicinal plants have a high Cd enrichment coefficient in the soil and are easy to be absorbed and accumulated into the body,which affects the quality of the medicinal materials.Therefore,this study adopted the method of potted experiment and used zeolite as the repairing agent.Firstly,the aging time of different concentrations of Cd and the influence of different concentrations and aging time on the growth of Anemarrhena asphodeloides and Leonurus japonicus were studied.Secondly,based on the appropriate addition ratio range of zeolite was preliminarily explored in 2mg/kg Cd contaminated soil,the effects of zeolites of different proportions were applied to soils with different Cd concentrations on the content of available Cd in soils and the content of Cd in two kinds of medicinal plants were studied,and the relationships between zeolite addition amount and plant growth were researched.Finally,the applied amount of zeolite in safe production of Anemarrhena asphodeloides and Leonurus japonicus in polluted soils by different concentrations Cd was obtained.The main findings are as follows:(1)The effects of different concentrations of exogenous Cd and aging time on the content of available Cd in soil and the growth characteristics of Anemarrhena asphodeloides and Leonurus japonicus were studied by pot experiment.The effective state content of Cd decreases rapidly after entering the soil,and then changed slowly until reaching equilibrium.When the concentration of exogenous Cd is less than 5mg/kg,the time for the available Cd in the soil to stabilize was 30 days.Different aging time of exogenous Cd less than 5mg/kg promoted the root length,plant height and leaf area of Leonurus japonicus.5mg/kg exogenous Cd inhibited the plant height within 20 days and promoted it at 40 days.Less than 1mg/kg of exogenous Cd promoted the dry weight of both Anemarrhena asphodeloides and Leonurus japonicus under different aging time,but the dry weight of 5mg/kg of exogenous Cd significantly decreased within 30 days of aging and significantly increased at 40 days of aging.(2)The application of zeolites in the soil with different Cd concentration promoted the growth indexes such as plant height,dry weight,root length and leaf area,and reduced the content of available Cd in soils and Cd concentration and the enrichment coefficient of Anemarrhena asphodeloides and Leonurus japonicus.Application of 2.5%zeolites in the soils with 0?1mg/kg Cd concentration achieved the best restoration effects.The content of available Cd in soils decreased by 30.4%?48%,the Cd content in Anemarrhena asphodeloides and Leonurus japonicus decreased by 20.4%?35.4%and 22.4%?47.9%respectively.Compared with the control,the maximum increase values of plant height,root length and dry weight of Anemarrhena asphodeloides and Leonurus heterophylla were 45.1%and 85.1%,118%and 102%,116.7%and 127.5%respectively.The Cd enrichment coefficient of Anemarrhena asphodeloides was higher than that of Leonurus heterophylla in soil contaminated by Cd.When the concentration of exogenous Cd was 1mg/kg,the enrichment coefficient of each treatment was the highest,and the enrichment coefficient of Anemarrhena asphodeloides and Leonurus heterophylla was 0.83 and 0.79 when zeolite was not added into soils,respectively,but the enrichment coefficient decreased mostly compared with the control group when zeolite was added to 2.5%and the enrichment coefficient were decreased by 0.21 and 0.24 respectively,.The pH of soil increased by 0.1?0.19 units,the bulk density increased by 0%?8.4%and the porosity decreased by 0%?5.1%when zeolite was applied to soils with different Cd concentrations,especially in soils with 2.5%zeolite.(3)The growth indicators of Anemarrhena asphodeloides and Leonurus heterophylla increased with the addition of zeolite in Cd contaminated soil,showing a significant positive correlation(P<0.01).The soil pH was positively correlated with the growth of the length and dry weight of Leonurus japonicus(P<0.05).All the growth indicators except the root length of Anemarrhena asphodeloides and Leonurus japonicus was significantly positively correlated with the soil bulk density,and was significantly negatively correlated with the soil porosity.The content of available Cd in soil decreased with the increase of zeolite content,showing a significant negative correlation(P<0.01).The Cd content of Anemarrhena asphodeloides and Leonurus japonicus was significantly and positively correlated with the available Cd content in soil(P<0.01).The addition amount of zeolite was significantly negatively correlated with the concentration of Cd(P<0.01)and the enrichment coefficient(P<0.05)of Anemarrhena asphodeloides and Leonurus japonicus.In summary,the optimal addition ratio of zeolites was 2.5%in the polluted soil with Cd concentration less than 5mg/kg.It can not only promote the growth of Anemarrhena asphodeloides and Leonurus japonicus,but also reduce the content of Cd in Anemarrhena asphodeloides and Leonurus japonicus and the available Cd content in soil,which provides important theoretical basis for the safe production of Anemarrhena asphodeloides and Leonurus heterophylla in the future. |
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