| Polycyclic aromatic hydrocarbons(PAHs)and heavy metals are two typical soil pollutants that can be accumulated and cause harm to human health via the food chain.Biochar is a solid product produced by the pyrolysis of biomass,with the characteristic of high carbon content,large specific surface area,abundant nutrients and more micropore structure and so on.It is currently widely used in compound contaminated soil remediation.When biochar enters the environment,it will undrgoageing under various biological and non-biological factors,changes its physical and chemical properties,and then changes its impact on the environmental behavior of pollutants.Studying the effect of aged biochar on the bioavailability of pollutants can assess the long-term application of biochar in the environment.In this study,corn straw was used as raw material to prepare fresh biochar and aged biochar.Through pot experiment of ryegrass,this study compares the effect of fresh and aged biochar on the changes of15 PAHs and three heavy metals(Cd,Cr,Pb)content in rhizosphere soil,non-rhizosphere soil,and aboveground and underground parts of plants used the cold atomic fluorescence quantification,flame atomic absorption spectrometry and high performance liquid chromatography.In addition,high-throughput sequencing technology is used to further detect microbial community structure changes in soil rhizosphere and non-rhizosphere soils,and the effects of aged biochar on the microbial community structure during the process of remediation of contaminated soils are explored.To provide a theoretical basis for the long-term application of biochar in contaminated soil remediation.The main findings are as follows:? The application of two kinds of biochar can increase the adsorption capacity of PAHs in soil and reduce the accumulation of PAHs in ryegrass.But the effect of aged biochar on reducing the cumulative amount of PAHs is less than that of the fresh biochar,that is,the adsorption capacity of aged biochar on PAHs in soil is weaker than the fresh biochar.In addition,there is a positive correlation between PAHs residues in soil and dose of biochar,but there is a negative correlation between cumulative amounts of PAHs in plants and applied doses of biochar.The accumulation of PAHs in the aerial part of the plant is lower than that in the underground part,and the residual amount of PAHs in the rhizosphere soil was lower than that in the non-rhizosphere soil.For example,at the application rates of 2% and 5%,the concentration of PAHs in the aged biochar amended soils ismade up of 69.55%-71.9% to the total amount of initial PAHs in soil;the addition of fresh biochar added the total amount of PAHs in the soil to the initial soil concentration.74.68%-79.8%.The cumulative effect of biochar on PAHs accumulation in ryegrass was opposite to that on PAHs in soil.Under the same 2% and5% application rates,the fresh biochar added soil increased the amount of PAHs accumulated in plants to the initial soil concentration.24.96%-19.41%;Adding aged biochar to the accumulation of PAHs in ryegrass plants is 30.08%-27.53% of the initial soil concentration.? The application of two kinds of biochar can increase the adsorption capacity of heavy metals in soil and reduce the accumulation of heavy metals in ryegrass.However,the aged biochar has a higher adsorption capacity for heavy metals in soil than the fresh biochar.At the applied doses of 2% and 5%,the residual contents of lead,cadmium,and chromium in the aged biochar-treated soil are 89.36%-93.6%,78.59%-80.69%,and 60.05%,-66.85% respectively,of the initial soil concentration,which is significantly higher than the residual amount of various metals in the fresh biochar treatment groups at the same dose(90.58%-92.46%,78.17%-78.92%,51.52%-59.19%);The cumulant variation trend of lead,cadmium,and chromium in ryegrass is opposite to the change trends of heavy metal residues in soil.In the 2% and 5%aged biochar treatment groups,the accumulation of three heavy metals in ryegrass(Pb: 10.63%-6.39%,Cd: 21.41%-18.24%,Cr: 39.94%-33.51%)is significantly lower than that in the fresh biochar treatment group at the samedose,(Pb: 9.41%-7.53%,Cd: 21.81%-21.08%,Cr: 48.47%-40.81%);in addition,the residues of three heavy metal in the rhizosphere are higher than those in non-rhizosphere soils.The accumulation of heavy metals in the underground part of the plant is significantly higher than that in the aboveground parts.? The two kinds of biochar have a great influence on the microbial community structure in the rhizosphere soil.The application of both biochar reduce the total amount of microorganisms and diversity in the soil.Compared with the fresh biochar,aging biochar treatment resultes in less total rhizosphere microorganisms numbers and reduced microbial diversity,but the numbers of dominant bacteria that could degrade PAHs in soil increased.This is related to the higher residual PAHs and heavy metals in rhizosphere soils treated with aged biochar.In addition,the dominant microorganisms in soils treated with two types of biochar is actinomycetes and proteobacteria... |
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