Effect Of Plants On The Remediation Of Cadmium And Pyrene Compound Polluted Soil

In recent years,due to the overall gross development of agriculture and industry in China,the emission of heavy metals and organic pollutants in the environment will remain at a relatively high level for a period of time,and soil pollution will therefore become more complicated and serious.According to reports in recent years,soil pollution is not only a single source of pollution,heavy metal and organic compound pollution has become an urgent problem to be solved.In this study,cadmium(Cd)and pyrene were selected as research objects.Pot experiments were conducted to study the growth status and pollutant removal ability of ryegrass(Lolium perenne L.),tall fescue(Festuca arundinacea Schreb.),alfalfa(Medicago sativa L.)and white clover(Trifllium repens L.)in the compound polluted soil.The effect of pollutant concentration on the optimal plant removal efficiency was studied.Experimental study on the removal of pollutants by optimal plant combined with biochar reveals the internal mechanism of plant removal of pollutants.Finally,the microbial community with strong resistance to Cd stress and effective degradation of pyrene was screened out by high-throughput measurement.The main research results are as follows:(1)The results showed that ryegrass had a good effect on the removal of pollutants.It was selected as an efficient plant to carry out the next stage of the experiment.High temperature(30?)had an inhibitory effect on the removal of pollutants.It was found that ryegrass and tall fescue had a significant effect on Cd(16.8mg/kg)and pyrene(71.04)mg/kg),but alfalfa and white clover were less resistant to pollutants.The removal of pollutants from plants found that ryegrass was resistant to Cd and the removal of Pyr was 18.73% and 65.72%,and that of tall fescue was14.69% and 50.36%,respectively.Under high temperature(30?),ryegrass had a poor effect on the removal of Cd and pyrene,which were 13.03% and55.86%,respectively.(2)It was found that the concentration of Cd had a great influence on the removal of pollutants.With the gradient of Cd concentration rising from 3.4,16.8,22.5 and 34mg/kg,the removal rate of the combined pollutants of Cd and Pyr by plants decreased significantly,while the removal rate of pollutants at low Cd concentration(3.4 mg/kg)was the highest,and high concentration of Cd would inhibit the removal of pollutants by plants.Pyr at low concentrations has different effects on Cd and Pyr removal,and as Pyr concentration increases,the plant's ability to remove pollutants increases.Over time,Pyr in ryegrass tissue will decrease,and Cd in ryegrass will increase and remain at a saturation level.(2)The results showed that with the increase of Cd concentration,the removal of pollutants by plants decreased significantly.With the increase of pyrene concentration,the ability of plant to remove pollutants will be enhanced.Pyrene in plants will decrease with the increase of time,Cd is the opposite.The pot experiment was used to study the ability of the ryegrass plant to remove two types of pollutants in Cd-Pyr compound contaminated soil.Set 5 Cd pollution concentrations(2.4,3.4,16.8,22.5,34 mg/kg)and 5 Pyr pollution concentrations(0,14,71.04,105.5,140 mg/kg)respectively,and cross-process the Cd and Pyr pollution levels respectively.It was found that the concentration of Cd had a great influence on the removal of pollutants.With the gradient of Cd concentration rising from 3.4,16.8,22.5 and 34mg/kg,the removal rate of the combined pollutants of Cd and Pyr by plants decreased significantly,while the removal rate of pollutants at low Cd concentration(3.4 mg/kg)was the highest,and high concentration of Cd would inhibit the removal of pollutants by plants.Pyrene of low concentration has different effects on CD and pyrene removal,and with the increase of pyrene concentration,the ability of plant to remove pollutants will be enhanced.Over time,Pyr in ryegrass tissue will decrease,and Cd in ryegrass will increase and remain at a saturation level.(3)Through pot experiment,the potential of eggplant straw biochar to strengthen ryegrass to repair Cd-Pyr compound contaminated soil was studied.The experiment set the target pollution concentrations of Cd(16.8mg/kg)and Pyr(71.04mg/kg),and the biochar dosage of 1%,3%,5% of the experimental treatment.The research results show that the application of biochar will increase the germination rate,biomass and removal of pollutants to a certain extent.This effect will also increase as the content of biochar rises.and the biochar and soil reached the highest when the mass ratio of 3% but 5% of biochar content will create inhibit plant growth and pollutants removal.Pyr in ryegrass tissue increased with biochar,but 5% biochar decreased the positive effect.However,the content of Cd in ryegrass tissue was negatively correlated with the amount of biochar applied.(4)The results showed that planting ryegrass significantly increased microbial diversity and richness,while adding biochar significantly decreased microbial diversity and richness.Lysobacter and Luteimonas are not only resistant to Cd,but also effective bacteria for pyrene degradation.Six different treatments were set up in the experiment.High-throughput sequencing of soils under different pollution conditions showed that the microbial diversity and abundance increased significantly when ryegrass was planted,and decreased when biochar was added;in addition,it is more affected by compound pollutants than single pollution.Screened for microorganisms that have a specific response to Cd and Pyr: Proteobacteria and Actinobacteria microorganisms will be significantly reduced by Cd pollution,but this toxicity can be reduced by adding Pyr;Gemmatimonadaceae has strong resistance to Cd pollution;Gemmatimonas and Gp6 are two bacterial genera with strong tolerance to Cd;Lysobacter and Luteimonas are not only resistant to Cd but also effective Pyr degradation bacteria.