| Cadmium has been widely concerned with the characteristics of strong mobility,high toxicity and wide range of pollution,Cd exceeded the most serious in our country.Phytoremediation is a promising green remediation technology with the advantages of low cost,no secondary pollution,less disturbance to the environment.At present,the research on the effects of heavy metal pollution on plants is mainly concentrated on crops and cash crops,the study of urban greening plants mostly focus on aquatic plants herbs and other plants with shorter growth period,the study of tree species was mainly concentrated on Salix and Populus;the research methods are mostly based on hydroponic experiment in laboratory or in vitro leaf soaking method,assessment of heavy metal repair potential lack of field experiment data support,based on this,conduct a preliminary study on the tolerance performance and ability to enrich and transfer Cd of potted annual seedlings of Cinnamomum camphora,Cinnamomum japonicum,Diospyros lotus,Ginkgo biloba and biennial Ginkgo biloba seedlings under cadmium stress in soil and atmosphere,through the physiological response,trait expression and accumulation of cadmium of the four kinds seedlings of landscaping tree species under different concentrations of Cd(Cd Cl2·2.5 H2O)contaminated soil and Cd sprayed leaves in filed.The main results are as follows: 1.Physiological responses of four tree species seedlings to Cd pollutionUnder the soil Cd pollution,the indexes of protection(SOD activity,soluble sugar content,proline content)and stress index(MDA content)showed the trend of increasing first,then decreasing,and finally stabilized,the photosynthetic indexes(chlorophyll content,net photosynthetic rate,transpiration rate)showed the trend of decreasing first and then increasing with the extension of treatment time.The physiological responses of different tree species to soil Cd stress were different.The Cd resistance indexes were stable when Cd stress lasted for 50 d.,When the leaves were contaminated by Cd,the change trend of Cd tolerance indexs were basically the same as that under soil Cd stress with the extension of treatment time,when Cd stress lasted for 50 d,soluble sugar content increased with the concentration increasing trend after the first rise and fall,the proline content and MDA content increased with the concentration increased,the chlorophyll content,net photosynthetic rate,transpiration rate increased as the concentration decreased gradually,the SOD activity of Cinnamomum camphora,Cinnamomum japonicum,Ginkgo biloba increased with the increase of treatment concentration,the SOD activity of Diospyros lotus showed a trend of increasing first and then decreasing.2.The character of four tree species seedlings under Cd pollutionUnder the soil Cd pollution,index growth of every specie(plant height,ground diameter,root length,root diameter,leaf area,biomass)generally showed a downward trend with the increase of treatment concentration,in particular,Cinnamomum camphora in T1(0.26 mg/kg),T2(2.16 mg/kg)group and Cinnamomum japonicum in T1(0.26 mg/kg)treatment group showed slightly stronger growth than the control group.All the tree species in high concentrations of Cd(50.16 mg/kg),the growth index significantly lower than the control,the biomass per plant of Cinnamomum camphora,Cinnamomum japonicum,Diospyros lotus,annual Ginkgo biloba and biennial Ginkgo biloba decreased respectively 33.15%?48.88%?81.50%?49.09%?57.50%.When the leaves were contaminated by Cd,the effects were the same as the the effects of soil Cd pollution on the characteristics of each tree species basically,index growth of every specie(plant height,ground diameter,root length,root diameter,leaf area,biomass)generally showed a downward trend with the increase of treatment concentration as well,the greater the concentration,the stronger inhibition of plant growth,the growth of Cinnamomum camphora,Cinnamomum japonicum,Diospyros lotus,annual Ginkgo biloba and biennial Ginkgo biloba decreased respectively were the worst in the T4 treatment group(50.16 mg/kg),decreased respectively 51.93%?56.43%?68.65%?67.64%?66.88%.3.The accumulation characteristics of four tree species seedlingsUnder the soil Cd pollution,the accumulation of Cd in all treatment groups were sequenced as following:root,stem,leaf,the roots of Cd accumulation amount accounts for 39.54-89.28% of the total plant absorption,the enrichment was the highest in the T4 treatment group(50.16mg/kg).In terms of the average of BCF and TF,the accumulation and transport capacities of Cd in the aboveground parts of the several tree species were in an order of Cinnamomum japonicum(1.370,0.343)?Cinnamomum camphora(1.055,0.264)?annual Ginkgo biloba(0.938,0.234)?biennial Ginkgo biloba(0.572,0.143)?Diospyros lotus(0.297,0.074).According to the average value of single plant enrichment,the ability of cadmium enrichment were in an order of Cinnamomum camphora(80.329 ?g/plant)?Diospyros lotus(10.376 ?g/plant)?annual Ginkgo biloba(5.864 ?g/plant)?Cinnamomum japonicum(5.501?g/plant)?biennial Ginkgo biloba(4.625?g/plant),Cinnamomum camphora accumulated large biomass due to its own growth advantage,this advantage makes up for the disadvantages of its enrichment and transfer ability were weaker than Cinnamomum japonicum.When the leaves were contaminated by Cd,the distribution of Cd in the seedlings of all species showed:leaf> stem>root,Cd was mainly distributed in seedling leaves,the Cd content increased in stem and root showed no obvious increase with the increase of spraying concentration,the Cd content of every organ in T4 treatment group showed maximum increase.Cinnamomum camphora,Cinnamomum japonicum had the largest concentration per plant in the T4 group were 9.861 g/plant,2.303 g/plant,the growth of Diospyros lotus,annual Ginkgo biloba and biennial Ginkgo biloba were inhibited a lot and the biomass were severely reduced in T4 treatment group,they showed maximum value of single plant enrichment in T3 group,were 4.014 g/plant,0.600 g/plant,0.887 g/plant.Cd concentration in organs of Cinnamomum camphora and Diospyros lotus were less than Cinnamomum japonicum,but the two species makes the value of single plant enrichment greater than the other 3 species with the characteristics of rapid growth,high biomass per plant.The Cd tolerance of each tree species was evaluated by the comprehensive evaluation method of principal component analysis and subordinate function method.Under the soil cadmium pollution,according to the comprehensive score value the cadmium tolerance of all tree species were in an order of Cinnamomum camphora(0.745)?Cinnamomum japonicum(0.626)?annual Ginkgo biloba(0.461)?Diospyros lotus(0.455)?biennial Ginkgo biloba(0.410),this sorting was consistent with the growth of the tree species;When the leaves were contaminated by Cd,the sequence of cadmium tolerance was Cinnamomum camphora(0.631)?Cinnamomum japonicum(0.526)?annual Ginkgo biloba(0.462)?Diospyros lotus(0.461)?biennial Ginkgo biloba(0.441)?According to the tolerance and accumulation of Cd,Cinnamomum camphora has the advantage of strong ability of Cd resistance,enrichment and transfer and so on,Cinnamomum camphora has a strong application potential for remediation of Cd contaminated soil in the south and southwest China. |
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