| Lead(Pb)and Zinc(Zn)were the most common heavy metal pollutants in soil and has become a critical problem.Phytoremediation appears to offer an efficient,inexpensive and environmental-friendly to control the contaminated environment by Pb,Zn.The inhibition of photosynthesis is obvious to heavy metal stress.We selected one-year-old seedlings,Toona ciliata var.pubescensin,as study materials in the greenhouse.Three group of Pb and Zn were used in this experiment.They were at the concentration of lOg/L(Pb or Zn)using PbCl2 or ZnCl2,respectively,designed correspondingly as control(CK),Pb and Zn treatments,respectively.At the end of the treatment(referred to as 15 d and 30 d post-treatment),the influence of Pb and Zn on chlorophyll(Chi)fluorescence and plant growth of Toona ciliata var.pubescensin young plants was investigated.Pb and Zn contents in plant organs were measured and comparing the accumulation ability of Toona ciliata var.pubescensin to Pb and Zn.The results of the study will provide data support for the screening of resistant woody plants.The main conclusions are as follows:1.With the increase of stress time and treatment times of Pb and Zn,the gas exchange parameters of Toona ciliata var.pubescensin leaves were seriously affected,resulting in the significant decrease of maximum net photosynthetic rate(Pn),transpiration rate(Tr),stomata(conductance(Cond)and stomatal threshold(Ls),while the increase of intercellular CO2(C),non-stomata(limitation was the main reason for the decrease of Pn.By comparing the changes of gas exchange parameters under Pb and Zn stress,it was concluded that Zn inhibited the photosynthetic rate of Toona ciliata var.pubescensin leaves more strongly than Pb.2.The information provided by chlorophyll fluorescence parameters showed that the maximum photochemistry efficiency(Fv/Fm),actual photochemistry efficiency(ETR),photochemistry quenching(qP)and non-photochemistry quenching(NPQ)of Toona ciliata var.pubescensin leaves decreased significantly under Pb and Zn stress,indicating that the PSII reaction center of Toona ciliata var.pubescensin was destroyed under Pb and Zn stress,and the photochemistry pathway was blocked and the photoinhibition was obvious.The system starts up and dissipates excess light energy in the form of heat.With the increase of stress time and treatment times of Pb and Zn,Fv/Fm,ETR and qP of Toona ciliata var.pubescensin showed a general downward trend,but the downward trend of ETR in Zn treatment group was higher than that in Pb treatment group.In Zn treatment group,ETR was inhibited 15 days after the first treatment,and the response of ETR to light intensity appeared disorder 30 days after the second treatment of Pb.NPQ also showed irregular fluctuation,indicating that Zn treatment was more effective than that of Pb treatment.It greatly inhibits the electron transfer and energy flow of PSII of Toona ciliata var.pubescensin.At the same time,through the change of PSII light energy distribution,it can be seen that under the stress of Zn,the leaf had a strong photodamage phenomenon(YNO significantly increased).3.Under the treatment of Pb and Zn,the content of Pb and Zn in the roots,stems and leaves of Toona ciliata var.pubescensin was significantly higher than that in the corresponding parts of the control.Root is the main part of absorbing and accumulating Pb2+.Root absorption of Pb treatment group is 6.67-20.84 times higher than that of control group,stem and root absorption of Pb treatment group is 2.07-7.08 times higher than that of control group,and the accumulation of Pb in leaves is the least,only 2.46-6.49 times higher than that of control group.In the aspect of absorbing and accumulating Zn,the accumulation of root,stem and leaf is the same.From the migration ability of Pb and Zn in Toona ciliata var.pubescensin,it can be seen that the amount of Pb migrating to leaves is very small,while Zn can migrate to leaves in large quantities.4.Under the treatment of Pb and Zn,the absorption and accumulation of nutrient elements in Toona ciliata var.pubescensin leaves were different.The contents of P,K and Ca were higher under the treatment of Pb than those in the control,while the contents of Mg and Fe were higher and lower than those in the control.The contents of K and Ca in the leaves of Toona ciliata var.pubescensin treated with Zn were higher than those in the control,while the contents of P,Mg and Fe were significantly lower than those in the control(P<0.05).By comparing the mineral element contents measured at each time after the treatment of Pb and Zn,it can be concluded that the P,Mg and Fe contents in leaves of Toona ciliata var.pubescensin treated with Zn are significantly lower than those treated with Pb(except P value 15 days alter the first treatment of Zn).The K content in leaves of Toona ciliata var.pubescens in treated with Zn is significantly higher than that treated with Pb.The Ca content in leaves of Toona ciliata var.pubescensin treated with Zn is different from that treated5.PCA analysis showed that the damage of Pb on the leaves of Toona ciliata var.pubescesin was first manifested in the damage of photosynthetic organ function and the decrease of photosynthetic rate.With the increase of Pb stress,the absorption and accumulation of nutrient elements in leaves were also affected.The damage of Zn on Toona ciliata var.pubescensin leaves showed that the function of photosynthetic organs and the absorption and metabolism of nutrient elements were affected at the beginning.In summary,as a kind of poisonous pollutant that plants do not need,Pb is mainly enriched in roots,which has a significant impact on leaf photosynthesis.As a trace element needed by plants,Zn is easily absorbed and transported to leaves,which has a significant impact on leaf photosynthesis and nutrient uptake and accumulation in a short time,and its toxicity is more serious than that of Pb. |
PDF Full Text Request