Research Of Woody Plants Growth And Effects On Pb And Zn Forms In The Rhizosphere With Lead-zinc Tailings Modified By Peat Soil

Aim to research Woody plants growth and effects on Pb and Zn Forms in the Rhizosphere with Lead-zinc tailings modified by Peat Soil.Paulownia fortunei and Nerium oleander were used as materials.Two years Potted experiments were conducted under condition of modified lead-zinc tailings with concentrations of different peat soils.The first year was basic research.In the study,different peat soil concentrations(CK:0,A1:5%,A2:10%,and A3:15%)was used to modify tailings and taproot,lateral root,stem and leaf biomass and metal contents,Root architecture and pH value,organic matter(OM),Cation exchange capacity(CEC)and BCR in rhizosphere process(0,6,12months)was measured.In the second year,the optimized effect of phytoremediation was studied by increasing modifier concentration(CK:0%,A1:10%,A2:20%,A3:30%),and Boehmeria nivea(L.)Gaudich.were measured as contrst.The results of root architecture,rhizosphere soil pH and OM,cumulative and transfer coefficients for the three plants are as follows:Phytoremediation research under substrate amendments:(1)Both root biomass and underground biomass of P.fortunei and N.oleander showed a trend of improved A3>A2>A1>CK,but tree species and modifiers had a significant effect on the gro.wth of plant root growth(P<0.01),root biomass growth of Pfortunei was significant among treatments(P<0.05).but not for N.oleander.The combination of tree species and modifiers concentration had a significant effect on the increase of root growth indicators(P<0.01).Compared to CK,P.fortunei significantly increased root length,tips,volume and surface area of the Fine root(0<d<2mm),increased the root volume and surface area of the d>2 interval.But not significant for N.oleander except for 0<d<0.5 root length,tips and d>2 surface area.The contents of Pb and Zn in lateral roots of the two plants were significantly higher than those in other parts(P<0.05).Pb and Zn in P.fortunei were mainly concentrated in lateral roots and leaves.The root surface area and volume affected the content of root absorption,and the growth of P.fortunei Fine roots increased Pb,Zn absorption and accumulation.significantly.While N.oleander Fine root growth stagnation avoided the absorption and accumulation of Pb and Zn in the root system.(2)With the increase of modifier concentration,the content of extracTablele Pb in the rhizosphere soil was decreased,the reducible,oxidizable and residual Pb were increased;the extracTablele Zn was decreased,the reducible and oxidizable Zn were increased,while residual was reduced.With the increase of treatment time,the content of extracTablele Pb was decreased,the reducible and oxidizable Pb were decreased,and the residue Pb was increased.While the extracTablele and reducible Zn were increased in the rhizosphere,and the oxidizable and residual Zn were decreased.In the of P.fortune Rhizosphere process,the percentage of residual Pb from CK to A3 increased by 14.36%,16.43%,20.26%and 20.46%,respectively,and the residual zinc decreased by 18.89%,13.98%,6.95%and 8.84%,respectively.The proportion of residual Pb in N.oleander residues increased by 11.95%,14.27%,16.90%,and 19.40%,respectively,and the residual Zn decreased by 3.34%,2.71%,3.37%,and 0.90%,respectively.The rhizosphere process modifiers can increase the passivation of Pb,decrease the release of Zn,and the passivation of Pb in P.fortune rhizosphere soil is better than N.oleander,but the release of Zn is higher than that of N.oleander.(3)With the increase of the concentration of the modifier,the pH value of the plants did not change significantly,but the OM in the rhizosphere soil increased significantly.With the treatment time increasing,the rhizosphere pH of the P fortune and N.oleander increased by 0.2 and 1.2 units respectively,and the content of OM in the rhizosphere did not change significantly.However,the increase was significant when the plants were not in the backgroxund,and the contents increased by 8.723 g·kg-1 and 3.93 g kg-1,respectively.OM and CEC were positively correlated with the oxidizable and reducible states of Pb and Zn respectively,or negatively correlated with the extracTablele state.The correlation between OM and CEC was significant.The effect of pH on the morphology of lead and zinc in the rhizosphere varied from plant to plant.The main reason for the change of lead and zinc forms in rhizosphere is the change of organic matter content in rhizosphere caused by the improvement.Research of Optimizing Phytoremediation Effect under Modified Proportion(1)With the increase of the modifier concentration,the total biomass of the three plants increased.The increments showed the trend of A3>A2>Al>CK but the roots had different growth patterns.The growth of fine roots increased significantly in B.nivea,and the ratio fine root/lateral root biomass increased from 19%to 32.9%.The difference between the root length and the root tip length of 0<d<1 was significant(P<0.01),corresponding to a 0<d<1 fine root surface area greater than d>1(P<0.01);In P.fortunei root system?the growth of root volume and surface area of d>2 interval was extremely significant(P<0.01)and all architecture index increase significant in 0<d<1 interval(P<0.05),while the growth of of N.oleander was relatively low.The greatest surface area of fine roots lead to high Pb and Zn content in the lateral roots of B.nivea.Pb and Zn in B.nivea lateral roots absorbed 1364.7 mg·kg-1 and 719.48 mg·kg-1 were found respectively.The content of Pb and Zn in the rhizosphere of three plants after planting were different.The order of Pb content was B.nivea>N.oleander>P.fortune;Zn content followed by P.fortune>N.oleanderr>B.nivea,In P.fortune rhizosphere,from CK to A3 were reduced by 1161.85 mg kg-1 1128.49 mg kg-1,1796.68 mg kg-1 and 1849.95 mg kg-1,respectively.In B.nivea rhizosphere,it decreased by 279.14 mg·kg-1,284.61 mg·kg-1,301.64 mg·kg-1 and 608.06 mg·kg-1,.Differences in plant root architecture lead to differences in soil lead and zinc removal,(2)The rhizosphere pH of the three plants decreased significantly(P<0.05),and the OM increased significantly(P<0.05).The rhizosphere pH and OM increased in the three plants.There was an increase of OM in the rhizosphere>B.nivea>N.oleander,pH size with N.oleander>P.fortune>B.nivea.There was a positive correlation between OM and root growth.The positive correlation between root length,surface area,volume growth and OM and P.fortune was significant respectively(p<0.05).There was a negative correlation between Fine root growth and pH,and there was a significant negative correlation between N,oleander Root tip number,Volume and pH N.oleander(p<0.05),and the root surface area and volume of P.fortune had significant negative correlation with pH(p<0.05).(3)Compared with the 5%,10%and 15%peat treatments,the transfer amount coefficient of Pb and Zn in shoots increased with the increase of the modifies concentration in B.nivea and P.fortune,while the transfer amount coefficient of Pb and Zn in N.oleanders decreased after 10%treatment,the best modified ratio of N.oleander is 10%.