Study On The Properties Of Lead And Cadmium In The Root Enriched Soil Of Reed And The Structure Characteristics Of Rhizosphere Biological Community

With the development of industrialization,heavy metal pollution in water and soil has become a serious problem in the world.Phytoremediation technology has the advantages of being environmentally protection.Using plants to absorb and enrich heavy metals in water and soil has become a research hotspot in the field of environmental pollution remediation.We choose reed as the research object,and the pot experiment method is used to investigate the ability of reed roots to adsorb and enrich soil Cd and Pb under different heavy metal concentrations.Analyze the physical and chemical properties of reed rhizosphere soil and its microbial community structure during the restoration process,and explore the absorption and enrichment mechanism of soil Cd and Pb by reeds in the soil environment.The study on Cd and Pb adsorption by Phragmites australis roots showed that the accumulation of heavy metals by Phragmites australis roots had a certain correlation with the pollution concentration during the same growth period.The higher the concentration of heavy metals in the soil,the greater the accumulation of heavy metals in the roots.When the concentration of Cd was 50mg/Kg,the maximum concentration of Cd in Phragmites communis could reach 1.248mg/Kg.When the concentration of lead was 400mg/Kg,the maximum concentration of Pb in Phragmites chinensis could reach 3.963mg/Kg.As the phytoremediation process proceeds,the accumulation of six heavy metal speciation in the roots showed an obvious trend of increasing.In the roots of Ph.australis,the maximum proportion of the sodium chloride extracted cadmium(SCD)and the acetic acid extracted lead(APB)were 47% and 34%,respectively.The migration and availability of Pb were greatly reduced.The changes of physical and chemical properties of rhizosphere soil during remediation were analyzed.The results showed that the physical and chemical properties of rhizosphere soil were significantly affected.In the process of phytoremediation,the proportion of residual state of Pb increased to 42%,and the proportion of residual state of Cd increased to 48%.In the early stage of phytoremediation,heavy metal Pb and Cd ions were largely fixed after entering the soil and were transformed into other relatively stable forms during the process of phytoremediation.During the whole experiment period,regardless of the addition of heavy metal concentration,the p H value of rhizosphere soil in the late stage of phytoremediation was higher than that in the early stage,which increased by about2%.The electrical conductivity in the late phytoremediation period was lower than that in the late phytoremediation period.The metal ions in the soil were adsorbed and fixed and gradually transformed to a stable form,and the content of movable Pb and Cd ions decreased,leading to the decrease of electrical conductivity.With the increase of Pb and Cd concentration,the enzyme activity of Phragmites australis rhizosphere soil was inhibited more obviously.Urease plays an important role in soil nitrogen transformation.When the concentration of Cd was 20mg/Kg and 25mg/Kg,the activity of urease in rhizosphere soil of Phragmites australis showed a trend of rapid decrease at first and then slow balance with time,and the microbial community gradually became stable after gradually adapt to the polluted environment.Under the treatment concentration of 20mg/Kg,the urease activity in the rhizosphere soil of reed increased firstly and then decreased,indicating that the low concentration of Cd increased the urease activity in the rhizosphere soil of plant and stimulated the activity of root exudates and soil microorganisms.Cd can inhibit the activities of sucrase and catalase in rhizosphere soil.The analysis of the microbial community structure in the rhizosphere of reeds showed that the structure and diversity of the microbial community in the rhizosphere of reeds were significantly different between the early and late phytoremediation.For Cd,the abundance of the dominant bacteria Actinomycota,Bacteroides and Patescibacteria in the rhizosphere soil of reeds increases with the increase of Cd concentration;Firmicutes,Acidobacteria,Chlorocurve and Deformation The abundance of the phylum was reduced;while the fungal communities were Xylaria,Acremonium,and plant endophytes increased in abundance in the soil samples treated with Cd in the early stage of phytoremediation,and the relative abundance of Xylaria increased with Cd The increase in treatment concentration increases.The abundance of Candida and silk coat molds were reduced.For Pb,the abundance of Actinomycota and Bacteroides in the rhizosphere during the early stage of repairing increased,while the abundance of Patescibacteria decreased.The relative abundance of Xylaria in fungal communities increased under low-concentration treatments,while the relative abundance of Candida decreased.Compared with the blank control group,the relative abundance of silk coat mold decreased under low concentration treatment conditions,and the relative abundance increased significantly under high concentration treatment conditions.