| Hunan is rich in lead-zinc mineral resources and is one of the five major lead-zinc production bases in China.The extensive exploitation of lead-zinc deposits has resulted in 13%of the soil contaminated by heavy metals in Hunan Province.Therefore,it is an important basis for the restoration and reconstruction of the contaminated area.In the process of phytoremediation of heavy metal contaminated soil,woody plants have attracted wide attention due to their high biomass and the ability to enrich a variety of heavy metals.In this study,2-year-old Melia azedarach L.seedlings were selected as the research object,and three gradients of lead-zinc slag to soil quality were set up(CK:100%soil;A:10%slag+ 90%soil;B:25%slag + 75%soil;C:50%slag + 50%soil).After one year of planting,the response of growth indicators and chlorophyll fluorescence parameters of Melia azedarach L.to heavy metal stress was studied,and the absor;ption and bioaccumulation of Melia azedarach L.to heavy metals were analyzed.In order to explore the adaptive potential of Melia azedarach L.under lead-zinc slag pollution and provide scientific basis for the potential of Melia azedarach L.to remediate heavy metal contaminated soil.The main results are as follows:(1)Lead,zinc,copper and cadmium are the four major hea'vy metals in lead-zinc slag contaminated soil.The main forms of Pb,Zn,Cu and Cd in soil unplanted Melia azedarach L.in each treatment group were reducible,acid extractable,residue and residue respectively.The main forms of Pb,Zn,Cu and Cd in soil planted Melia azedarach L.were reducible,oxidizable,oxidizable and residue respectively.The mobility factors of Pb and Cd in soils of all groups were as follows:planted Melia azedarach L.>unplanted Melia azedarach L.,the opposite trend of Zn and Cd,indicating that Zn and Cd were transformed into more stable forms,while Pb and Cd were more active.(2)With the increase of the mass ratio of lead-zinc slag in soil,the plant height,relative growth rate and SPAD value of Melia azedarach L.showed CK>A>B>C and the difference was significant(p<0.05).The results showed that lead-zinc slag inhibited the growth of Melia azedarach L.,and the larger the mass ratio,the more obvious the inhibition.However,the plant height at the end of the experiment was significantly higher than that at the beginning of the experiment,indicating that Melia azedarach L.could still grow in the soil polluted by lead-zinc ore residue.(3)With the increase of the mass ratio of lead-zinc slag in soil,the maximum fluorescence yield(Fm),the maximal photochemical efficiency of PS ?(Fv/Fm)and the latent PSII quantum yield(Fv/F0)of Melia azedarach L.all showed a downward trend.It can be seen that the activity index of leaves of Melia azedarach L.decreased,leading to the reduction of conversion efficiency of primary light energy.The rapid light-response of chlorophyll fluorescence parameters of leaves of Melia azedarach L.showed that the effective PSII quantum yield(Y(?))and coefficient of photochemical quenching(qP)decreased as light intensity rised and showed CK>A>B>C in general,while the parameters of quantum yield of regulated energy dissipation(Y(NPQ),coefficient of non-photochemical quenching(qN)and electron transfer rate(ETR)were increased.while PSII regulated the quantum yield(Y(NPQ),non-photochemical quenching parameter(qN)and apparent electron transfer rate(ETR)of energy dissipation.Y(NPQ)and qN showed an upward trend with the increase of light intensity.Y(NPQ)and qN were C>B>A>CK,ETR was CK>A>B>C.On the 30th day,the light intensity of rate showed a downward in group A and group B was 613 and 863?mol·m-2·s-1 respectively,while that was 1297?mol·m-2·s-1 in group C and approached saturation.The results showed that with the increase of the mass ratio of lead-zinc slag in soil,the blocked degree of electron transfer increased,while the energy share used in photochemical reaction pathways is reduced,and Melia azedarach L.could only dissipate excess light energy by increasing non-photoc-hemistry quenching pathway,in order to avoid damage to the photosystems.(4)The accumulation of lead,zinc,copper and cadmium in different parts of Melia azedarach L.in soils contaminated with Lead-Zinc slag of different gradients were as follows:C>B>A>CK,and the difference was significant.Root is the main part of accumulation of Pb and Cu in Melia azedarach L.,the second was leaf,root was the least.The translocation factors of Melia azedarach L.to Pb,Zn,Cu and Cd were Cd>Zn>Cu>Pb,and the accumulator factor of aboveground parts and roots to four heavy metals was Cd>Cu>Zn>Pb.(5)The contents of Pb,Zn,Cu and Cd in Melia azedarach L.were negatively correlated with the growth indexes(growth of plant height,growth of ground diameter,relative growth rate,SPAD value)and chlorophyll fluorescence parameters(Fm,Fv/Fm,Fv/Fo)of Melia azedarach L.(p<0.01),indicating that the inhibition of growth of Melia azedarach L.was the result of the effects of Pb,Zn,Cu and Cd in Melia azedarach L.,this inhibition can be reflected by the changes of chlorophyll fluorescence parameters.In summary,lead-zinc slag can inhibit the growth of Melia azedarach L..In soils polluted with the mass ratio of 10%and 25%lead-zinc slag,Melia azedarach L.can protect the light system and ensure its growth through photosynthetic regulation mechanism.Therefore,Melia azedarach L.can be used as a potential woody plant for remediation of lead-zinc mine waste contaminated soil. |
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