| An increasing number of human activities make the problem of soil heavy metal pollution more and more severer.The excessive heavy metal in soil may cause considerable detrimental effects on plant.Its main performances are from the molecular to the cellular structure,physiological metabolism,external morphology and so on.Especially,the significant symptom that heavy metal affect plant is the inhibition of photosynthesis.In recent years,chlorophyll fluorescence technique can detect the physiological condition of plants' photosynthesis by the means of rapidness,simpleness and convenience,accurateness and non-invasion,which make it popularize quickly and apply widely to physiological ecology of plants' photosynthesis and environmental stress.However,so far,the related reports that chlorophyll fluorescence technique was applied to research the response of leaves PS? photochemical efficiency in woody plants to heavy metal stress is very few.Therefore,the study selected two kinds of woody plant,Koelreuteria paniculata and Schima superba,as research objects,which are usually used to afforestation on hillside in subtropical area.And the study adopted the method of indoor cultivation and the method of artificial simulation of heavy metal Pb contaminated soil:400mL of 10g/L PbCl2 solution was spiked in soil of each pot.Chlorophyll fluorescence parameters were measured on the 10th day and 35th day after every spike.Then second spike was carried out.By that analogy,a total of spike times was 3.Thus,the study researched the responses of PSII photochemical efficiency,distribution of light energy and excessive light energy dissipation in two types woody plants to Pb.On this basis,the study found out and analyze the quantitative responsive relation of the content of Pb and woody plant PSII.The results of the study provided theoretical foundation in aspects of woody plants screening and adversity physiological ecology.The results of the study followed:(1)Compared with the control,the values of Fv'/Fm',Fq'/Fv',Rfd and Fv/Fm of Koelreuteria paniculata young plants had no significantly change with accumulation of times of spikes(P>0.05).Compared with the control,the tendency of the values of Fv'/Fm',Fq'/Fv' Rfd and Fv/Fm of S.superba young plants was negative firstly and positive subsequently with accumulation of times of spikes.However,compared with the control,PSII photochemical efficiency of S.superba young plants was affected significantly on 35th day after first spike PbCl2 solution(P<0.05).The results reflected that Pb had no significantly negative effect on the efficiency of excitation energy capture and the efficiency of energy capture of Koelreuteria paniculata young plants,but had significantly negative effect on that of S.superba young plants,namely PSII of S.superba young plants partly was inactive under Pb stress.(2)Compared with the control,the values of Y(?),Y(NO),Y(NPQ)of Koelreuteria paniculata young plants had no significantly change with accumulation of times of spikes(P>0.05).Compared with the control,the tendency of the values of Y(?)of S.superba young plants was negative firstly and positive subsequently with accumulation of times of spikes,but the tendency of the values of Y(NO),Y(NPQ)of S.superba young plants was positive firstly and negative subsequently with accumulation of times of spikes.However,compared with the control,the ratio of dissipative ways of excited energy absorbed by PSII of S.superba young plants was affected significantly on 35th day after first spike PbCl2 solution(P<0.05).The results reflected that Pb had no significantly negative effect on the ratio of dissipative ways of excited energy absorbed by PS? of Koelreuteria paniculata young plants,but had significantly negative effect on that of S.superba young plants,namely the share that the excited energy absorbed by PS? of S.superba young plants was used to electron transport of PS? reaction center was reduced,but the share that the excited energy absorbed by PS? of S.superba young plants was dissipated by heat was increased under Pb stress.Compared with the control,the values of P,D,1-qL of Koelreuteria paniculata young plants had no significantly change with accumulation of times of spikes(P>0.05).Compared with the control,the tendency of the values of P of S.superba young plants was negative firstly and positive subsequently with accumulation of times of spikes,but the tendency of the values of D,1-qL of S.superba young plants was positive firstly and negative subsequently with accumulation of times of spikes.However,compared with the control,the utilization of light energy absorbed by photosynthetic apparatus of S.superba young plants was affected significantly on 35th day after first spike PbCl2 solution(P<0.05).The results reflected that Pb had no significantly negative effect on the utilization of light energy absorbed by photosynthetic apparatus of Koelreuteria paniculata young plants,but had significantly negative effect on that of S.superba young plants,namely the share that light energy absorbed by photosynthetic apparatus of S.superba young plants was used to photochemical reaction was reduced,but the share that light energy absorbed by photosynthetic apparatus of S.superba young plants was dissipated by heat was increased under Pb stress,which meant Pb imbalanced between the utilization and capture of excited energy.(3)Compared with the control,the values of qL and the values of NPQ of Koelreuteria paniculata young plants had no significantly change with accumulation of times of spikes(P>0.05).Compared with the control,the tendency of the values of qL of S.superba young plants was negative firstly and positive subsequently with accumulation of times of spikes,but the tendency of the values of NPQ of S.superba young plants was positive firstly and negative subsequently with accumulation of times of spikes.However,compared with the control,fluorescence quenching of S.superba young plants was affected significantly on 35th day after first spike PbCl2 solution(P<0.05).The results reflected that Pb had no significantly negative effect on fluorescence quenching of Koelreuteria paniculata young plants,but had significantly negative effect on that of S.superba young plants,namely the share that light energy absorbed by PSII antenna pigments of S.superba young plants was used to photochemical electron transport was reduced,but the share that light energy absorbed by PSII antenna pigments of S.superba young plants was dissipated by heat was increased under Pb stress.(4)Compared with the control,with the accumulation of spikes times,the content of Pb in Koelreuteria paniculata young plants leaves was increased significantly under Pb treatment(P<0.05).The content of Pb was 1,2,2.5,2.7,2.75 and 3 times of that of the control in Koelreuteria paniculata young plants leaves on 10th day and 35th after first spike PbCl2 solution,on 10th and 35th day after second spike Pbl2 solution,on 10th and 35th day after third spike PbCl2 solution.The content of Pb was 1.78,2.31,3.85,4.11,4.44 and 4.33 times of that of the control in S.superba young plants leaves on 10th day and 35th after first spike PbCl2 solution,on 10th and 35th day after second spike PbCl2 solution,on 10th and 35th day after third spike PbCl2 solution.The content of Pb was 1.39,1.71,2.06,2.21,2.39 and 2.85 times of that of the control in Koelreuteria paniculata young plants stems on 10th day and 35th after first spike PbCl2 solution,on 10th and 35th day after second spike PbCl2 solution,on 10th and 35th day after third spike PbCl2 solution.The content of Pb was 5.11,8.89,12,12.58,13.79 and 14.15 times of that of the control in S.superba young plants stems on 10th day and 35th after first spike PbCl2 solution,on 10th and 35th day after second spike PbCl2 solution,on 110th and 35th day after third spike PbCl2 solution.The content of Pb was 8.78,19.44,23.67,39.87,45 and 54.42 times of that of the control in Koelreuteria paniculata young plants roots on 10th day and 35th after first spike PbCl2 solution,on 10th and 35th day after second spike PbCl2 solution,on 10th and 35th day after third spike PbCl2 solution.The content of Pb was 8.17,9.72,11.02,14.86,20.27 and 24.42 times of that of the control in S.superba young plants roots on 10th day and 35th after first spike PbCl2 solution,on 10th and 35th day after second spike PbCl2 solution,on 10th and 35th day after third spike PbCl2 solution.(5)The times of treatments had significant effect on Rfd,Fv/Fm,no significant effect on Fv'/Fm',Fq'/Fv' in Koelreuteria paniculata.Days of treatments did not affect Fv'/Fm',Fq'/Fv',Rfd,Fv/Fm significantly in Koelreuteria paniculata.The interaction of times of treatments and days of treatments affect Fv'/Fm',Rfd significantly in Koelreuteria paniculata.The times of treatments had significant effect on Fv'/Fm',Fv/Fm,no significant effect on Rfd,Fq'/Fv' in S.superba.Days of treatments affect Fv/Fm significantly in S.superba,did not affect Fv'/Fm/,Fq'/Fv',Rfd significantly in S.superba.The interaction of times of treatments and days of treatments affect Fv'/Fm',Rfd,Fq'/Fv',Fv/Fm significantly in S.superba.Negative correlation existed between the content of shoot Pb and photochemical efficiency,which were not significant in Koelreuteria paniculata.Correlation existed between the content of root Pb and photochemical efficiency,which were not significant in Koelreuteria paniculata.Negative correlation existed between the content of shoot Pb and photochemical efficiency on 35th after first spike,on 10th and 35th after second spike,which were significant in S.superba.Correlation existed between the content of root Pb and photochemical efficiency,which were not significant in S.superba.In conclusion,the spike of Pb accumulatively had influence on PS?photochemical efficiency of Koelreuteria panicula and S.superba young plants.By the means of the analysis of excited energy and fluorescence quenching,Koelreuteria panicula and S.superba young plants all could dissipated excessive energy by heat.However,the extent of inhibition of PS? photochemical efficiency of S.super ba young plants exceeded that of Koelreuteria panicula young plants,which maybe was relative to the high content in leaves of S.superba young plants. |
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