| Heavy metal contaminated soils is an increasingly serious environmental problems,phytoremediation is an environmentally friendly way of governance of heavy metals in soil,phytoremediation also has a broad reconstruction of vegetation,landscape restoration,improvement of soil properties and other functions.In this sense,woody plants with high biomass,long growth cycle as the preferred object.The toxic effects of heavy metals on plants are manifested in all aspects,in which plant photosynthesis is inhibited is a significant symptom of heavy metal toxicity.Our research applied pot experiment study on 1-year-old sapling of broad-leaf species Zelkova schneideriana and Koelreuteria paniculata,We tested photosynthesis and PSII chlorophyll fluorescence characteristic of K.paniculata and Z.schneideriana blade,and studied absorption and enrichment along with distribution ratio aspect in these plants,through four times’ continuous mixed PbCl2 and ZnCl2 into potted soils.Our research analyzed and compared the tolerance of two plants,under the single stress Pb、Zn and tried to find out the relationship between photosynthetic physiological parameters and contamination dose of Pb、Zn.The results will provide data for the screening of resistant woody plants.The main experimental findings are as follows:1.Four times’ Pb、Zn dealing,the maximum net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),and limited stomatal value(Ls)were significantly less than the control(P<0.05).Intracelluar CO2 concentration(Ci)was greater than the control and appeared that Pn decrease was cause by non-stomatal limitation.In the treatment group,the Pn,Tr,Gs and Ls of K.paniculata and Z.schneideriana were decreased,and Ci increased,with the increase of Pb、Zn treatments.Under the Pb and Zn stress,the Z.schneideriana showed higher photosynthesis than the K.paniculata.The heavy metal of Zn have stronger inhibition than Pb,in these two woody plants.2.Under the four times’ dealing of Pb、Zn,maximal PSII photochemical efficiency(Fv/Fm),actual photochemical efficiency(ETR),were lower than the control,and the ETR was significant lower than the control control(P<0.05).The significant decrease of photochemical quenching(qP)decreased and increase of non-photochemical quenching(NPQ)indicated that K.paniculata and Z.schneideriana occurred the photo inhibition phenomenon forced by Pb、Zn,but efficiently dissipated the excess light energy of PS II in the form of heat.With the increase of Pb.Zn treatments,the Fv/Fm,ETR and qPof two woody plants were decreased in the treatment group,and NPQ showed an increasing trend.In contrast the photoprotection of these woody plants on Pb,Zn stress,we concluded that treatment at low concentrations Pb,qP and NPQ of K.paniculata highter than Z.schneideriana,however,with the increase of Pb、Zn treatments the trend happened reverse,smaking Z.schneideriana showed higher photosynthetic capacity.In the Zn treatment,the Fv/Fm,ETR,qP,NPQ of the two woody plants were higher than those of the control,and the range of change were higher than Pb treatment,which indicated that the damage of Zn to these two plants was higher than that of Pb.The Z.schneideriana showed higher photosynthetic capacity than K.paniculata after the first Zn treatment;and after second and third Zn treatment,compared with the control,K.paniculata had wider the range of change of qP than Z.schneideriana,which indicated Z.schneideriana is more resistant to Zn stress.3.Under the four times’ dealing of Pb、Zn,the contents of Pb2+ and Zn2+ in the parts of K.paniculata and Z.schneideriana were significantly higher than those in the control.The most component for Pb2+ of two woody plants was root,the root absorption of Pb treatment group was 6.42-32.89 times higher than that of the control group;the accumulation capacity of stem lower than root,the stem absorption of Pb treatment group was 2.95-11.67 times higher than that of the control group;the accumulation of leaves slightly highter than stem,but on the increased times aspect,the leaves absorption of Pb treatment group was 2.63-8.85 times higher than that of the control group.The accumulation capacity of Pb of K.paniculata was highter than Z.schneideriana.Under the Zn treatment,the most component for Zn2+ of two woody plants was root and stem,the leaves was least.The accumulation capacity of Zn of K.paniculata was highter than Z.schneideriana,but the absorption of Zn was more sustainable in Z.schneideriana.The distribution of different heavy metals in plants is different.The distribution of Pb2+ from the soil in the roots accounted for 57.09%-76.68%of the total absorbed amount in the two woody plants,the number of the migrated to the stem was 6.95%-18.95%,and migrated to the leaves was 10.36%-30.32%of the total.The allocation ratio of in root、stem、leaves of Zn2+ Z.schneideriana was 42.99%、29.85%、27.16%、in K.paniculata was 37.17%、33.81%、29.02%,which indicated that the allocation rate of Zn2+ in K.paniculata and Z.schneideriana was higher than that of Pb2+ in the two plants.In the accumulation ratio,it decreased with the increase of the number of treatments,and the the accumulation ratio of K.paniculata to Pb and Zn was higher than that of Z.schneideriana.4.Based on the Lake model,the tolerance ability of Pb and Zn was studied under single Pb and Zn stress.The Pb tolerance of Z.schneideriana was higher than that of K.paniculata with the increase of the number of Pb treatments.The resistance of Zn to two plants was not strong,In contrast,the resistance to Zn of Z.schneideriana is higher than the K.paniculata.5.From the response of Pb、Zn in soil to photosynthesis、fluorescence characteristic,we can leam,K.paniculata seedling leave of soil Pb pollution tolerance range was between 1.80-2.15g/kg,Z.schneideriana was between 1.85-2.25g/kg.The damage caused by the continuous Zn treatment to the leaves of the K.paniculata and Z.schneideriana was similar to that of the Zn in the soil(《0.5g/kg),and the results showed that the resistance of two woody plants to Zn was not high.But from the cycle of test,the Z.schneideriana will survived serious polluted soil of Zn than K.paniculata. |
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