Research On The Remediation Potential And Tolerance Mechanism Of Wheatgrass To Pyrene And Nickel Co-contaminated Soil

Polycyclic aromatic hydrocarbons and heavy metals are two representative contaminants in the soil,often present in the soil simultaneously to form a co-contamination.Phytoremediation is applicable and environmentally friendly,and can be used for the remediation of soil pollution.However,for the co-contamination system,the researches of the migration and distribution of pollutants in plants,the risk in the crops and the interaction of the two contaminants are rare.In this study,wheatgrass was used as a repairing plant to remediate the pyrene-nickel?Ni?co-contaminated soil.The influence of wheatgrass to the removal efficiency and transformation of pollutants in the soil,the activity of soil enzymes;the growth and physiological characteristics of wheatgrass;the distribution characteristics of pollutants in plants and the interaction effects of two contaminants on the phytoremediation of contaminated soil by wheatgrass were investigated.The main findings are as follows:?1?Pyrene and Ni were mainly concentrated in the roots of wheatgrass?63%⁹0%?.The enrichment of pyrene and Ni in wheatgrass under single contamination was higher than that of co-contamination.After 40 days of cultivation,the removal rate of pyrene in the single contaminated soil with wheatgrass cultivation was the highest,reaching 49%.The accumulation of Ni in the single contaminated soil with wheatgrass cultivation was 1.5 times that of the co-contamination.The removal of pyrene and Ni in the soil was mainly by reducing the content of bioavailable contaminants.The proportion of bioavailable pyrene in the soil with wheatgrass cultivation was reduced by 11%to 38%,and the concentration of exchangeable Ni was reduced by 28%to 38%.In addition,Ni inhibited the soil enzyme activity,soil microbial activity and dissolved organic matter?DOM?content.Wheatgrass increased soil enzyme activity,soil microbial activity and DOM content.?2?Both pyrene and Ni had different inhibitory effects on the growth of wheatgrass,and the physiological and biochemical characteristics of chlorophyll content,malondialdehyde?MDA?content and antioxidant enzyme activity of wheatgrass changed under different pollution treatments.Pyrene single contamination had the least inhibitory effect on the growth of wheatgrass,compared with the control group,the plant height and fresh weight of wheatgrass did not change significantly.Ni single contamination had the greatest inhibitory effect on the growth of wheatgrass,compared with the control group,the plant height and fresh weight wheatgrass were reduced by11%and 12.8%,respectively.Under the stress of pyrene and Ni,the survival rate of plants in all treatment groups was higher than 85%,especially pyrene single contamination and co-contamination,and the survival rate was above 90%.Compared with the control group,the chlorophyll content of wheatgrass was reduced under pollution stress,and the contents of MDA,CAT and POD were increased.Among them,the content under single pyrene contamination was the highest,then was the pyrene-Ni co-contamination,the single Ni contamination was the lowest.The trends of MDA,CAT and POD content were:under single Ni contamination was the highest,then was the pyrene-Ni co-contamination,the single pyrene contamination was the lowest.?3?Pyrene can be transported by apoplast and symplast in wheatgrass,and the content of pyrene in the symplast was 2 to 3 times that of apoplast.The uptake of pyrene by wheatgrass at different pH was different,and the pH of the medium solution was changed during the uptake process.Under the treatment of Na₃VO₄,DNP and Zn²⁺,the absorption of pyrene by wheatgrass was significantly reduced,which indicated that the uptake of pyrene by wheatgrass related to H⁺transport and energy conversion,and pyrene can also be absorbed through the water-protein channel.Under the action of ATPase inhibitor and ATP production inhibitor,Ni content in wheatgrass were decreased by 29.5%and 27.4%,respectively,which indicated that the uptake of Ni was closely related to the synthesis and decomposition of ATP.In addition,under Ni stress,phytochelatin?PCs?content in wheatgrass increased by 20%²4.8%,and malic acid and acetic acid also increased significantly,and the highest increased by 180.3%and185.7%,respectively.These substances were involved in the detoxification process of Ni by wheatgrass.?4?In the roots of wheatgrass,pyrene and Ni mainly accumulated on the cell wall of plant cells.The content of pyrene and Ni can reach 54%and 65%or more,respectively,and Ni ws mainly present in the form of NaCl extraction.In the shoots,pyrene was mainly exist in the soluble fraction of the cells?58%?under the pyrene single contamination,and under co-contamination,pyrene mainly accumulate on the cell wall?57%?;under the Ni single contamination,most of the Ni?50.33%?was concentrated in the soluble fraction,while under the co-contamination,Ni was mainly enriched in the cell organelle?40.52%?,and the Ni content in the extracted HAc was the highest?57.31%⁷2.18%?.In general,both pyrene and Ni were concentrated in the cell wall and soluble fraction,and there are fewer in organelles,and the Ni content of the fluidity was relatively small.Ni in plants was mainly in the form of less fluidity.