| Soil contamination by heavy metals and persistent organic pollutants have been accelerated in China during the past decade because of rapid urbanization and industrialization.The output of heavy metals and organic pollutants into environment will stay in a comparatively high level in a long period.Soil contamination in China tends to be severe and complicated.Sites co-contaminated by heavy metals and organic pollutants have been documented in recent.Therefore,the development environmental friendly,low-cost,and in situ strategies directed at co-contaminated sites is of great importance.Dendroremediation,which makes use of trees to clean up contaminations in soils,is popular in the application of phytoremediation.Willow species have been suggested to use in the remediation of contaminated soil due to their high biomass production,fast growth,and high accumulation of heavy metals.These characteristics make it possible to repair contaminated soil with energy value and economic benefits.In this study,a pot experiment was carried out in greenhouse conditions to examine the remediation efficiency of three willows(Salix×aureo-pendula CL ’J1011’、Salix ×Jiangsuensis ’J172’、Salix×Jiangsuensis ’55’)on soil contaminated by cadmium(Cd)and pyrene(PYR).Secondly,chemical and agronomic strategies were also investigated to improve phytoremediation of Cd and pyrene co-contaminated soils.Finally,this study investigated the application of willow in flooded and cocontaminated soil with its growth and development,removal efficiency and eddect in soil.The main results are summarized in the following text:(1)Results showed that willows showed great endurance to Cd-P YR co-polluted soil,and simultaneous high ability in accumulation of Cd and dissipation of pyrene.The accumulation of cadmium in different tissues of willow was:leaf>stem>root.Among the willows,the leaves of Salix×Jiangsuensis ’55’ showed the highest accumulation of cadmium(by 74.98 mg·kg-1)in the single cadmium contaminated soil.However,the planting of Salix×Jiangsuensis ’55’ showed the highest concentration of pyrene(by 5.4 mg·kg-1)and lower concentration of Cd in Cd and pyrene cocontaminated soil,and the membrane lipid peroxidation of Salix ×Jiangsuensis ’55’ was the highest,which showed the poor environmental tolerance of Salix ×Jiangsuensis ’55 ’.Salix×aureo-pendula CL ’J1011’ showed remarkable accumulation of cadmium and a lowest concentration of pyrene in co-polluted soil(by 462.8 μg·kg-1 and 1.2mg·kg-1,respectively).The planted of Salix×aureo-pendula CL ’J1011’ enhanced urease and sucrase activity in single cadmium/pyrene single or complex contaminated soils.improved soil quality,and exhibited greater repair potential.(2)A pot experiment was conducted to investigate the potential for enhanced phytoremediation of co-contaminated soil by willow and application of citric acid.The addition of citric acid did not significantly affect the Cd distribution in willow,but inhibited the growth of willow and the absorption of Cd by willow in Cd contaminated soil.And the addition of citric acid did not significantly affect the growth of willow,but significantly increased the total extraction of Cd at Cd-PYR treatments(by 19.5%).The addition of citric acid did not significantly affect the dissipation of pyrene in pyrene single and co-contaminated soil,which showed that soil pollution types affected the efficiency of willow.In addition,the addition of citric acid significantly affected the synthesis of photosynthetic pigments in the leaves of willow,which was inhibited by single pyrene contaminated soil,and promoted under single Cd contaminated soil,but did not affected the net photosynthesis rate(Pn)and maximum quantum efficiency of photochemical(Fv/Fm),which indicated that the interaction of citric acid and Cd/pyrene did not significantly affect the photosynthetic system of the leaves of willow.However.the addition of citric acid inhibited the activities of sucrase and phosphatase in the soil and showed a negative effect on the soil environment.(3)A pot experiment was conducted to investigate the potential for enhanced phytoremediation of co-contaminated soil by willow and application of urrea.Compared with control treatments,urea application significantly increased the biomass of willow and the concentration of Cd in the aboveground tissues,and promoted the enrichment and transport of Cd by willow,so that the total extraction of Cd was significantly increased in single Cd and co-contaminated soil(by 98.7%and 199.5%,respectively).Urea application decreased the total extraction of pyrene by willow,whitch decreased 21.6%amd 43.6%in single pyrenen and Cd-pyrene co-contaminated soil respectively,but the removal of pyrene was not significantly changed by application of urea.The addition of urea increased pigment content,Pn,Tr,Fv/Fm and absorption of mineral nutrients(Ca,Mg,Fe,Mn,Zn)in willow,and also increased the activity of sucrase and phosphatase in the soil.These results showed that the application of urea can promote the absorption of Cd and the growth of willow,and improve the soil environmental quality.It can be used as a plant extract promoter in phytoremediation of willows.(4)In flooding experiments,soil flooding significantly increased the available concentration of Cd in the soil and the absorption of Cd in the roots,but reduced the concentration of Cd in the aboveground tissues of the willow,which displayed 34.1%and 31.9%decreases in the total amount of Cd extracted by willows in Cd and Cd-PYR treatment compared to its respective no-flooding treatments.Soil flooding also significantly inhibited the dissipation of pyrene in the soil,which displayed 39.4%and 46.3%decreases in PYR and Cd-PYR treatment compared to its respective no-flooding treatments.However,soil flooding promoted the synthesis of photosynthetic pigments in the leaves of willow,and increased the Pn,stomatal conductance(gs),Tr,quantum efficiency of photosystem(ΦPSⅡ)and photochemical quenching(qP)of leaves.However,soil flooding inhibited the absorption of K and Ca in the roots of willow and the activities of urease,sucrase and phosphatase in soil.Results showed that soil flooding greatly inhibited the ability of Salix×aureo-pendula CL ’J1011’ to repair contaminated soil. |
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