Effects Of Shading On Photosynthesis And Chlorophyll Fluorescence Of Tilia Mandshurica And Tilia Amurensis Seedlings

Light is one of the important environmental factors affecting plants.In this paper,two-year-old seedlings of Tilia mandshurica and Tilia amurensis Rupr were used as test materials for shading treatment,and the shading degree was set to 0%(control,CK)and 30%(light shading,LS).,60%(moderate shading,MS),90%(severe shading,SS).Through the analysis of changes in seedling morphology,photosynthetic characteristics,fluorescence characteristics and physiological indicators,combined with changes in environmental factors.Explore and analyze the response mechanism of linden tree seedlings to shading,and screen out suitable light conditions for growth.Provide a basis for a suitable light environment for the growth of seedlings.The main findings are as follows:(1)Shading promotes the leaf area,plant height and leaf growth of the two types of lime trees,and the promotion weakens with the increase of shading.Among them,the change in leaf area was the most significant.On the 35th day of treatment,Tilia chaff and Tilia amurensis increased by 17.22%and 32.02%respectively compared with the control under SS treatment.(2)Under shading,the yellow of the leaves of the two linden trees increases,the green becomes lighter,and the gloss decreases.The content of chlorophyll a,b and total chlorophyll increased,and the overall chlorophyll a/b showed a downward trend.When the severe shading(SS)treatment for 35 days,the content of chlorophyll a and b and the total chlorophyll of Tilia bran increased by 64.73%,114.26%and 75.98%respectively compared with the control(CK).Tilia amurensis increased by 141.94%,218.27%,and 162.64%respectively compared with the control(CK).(3)Shading can significantly affect the photosynthetic parameters of the two linden trees.Saturated vapor pressure difference(VPD)and leaf surface temperature(Tleaf)are the main environmental factors that affect the photosynthetic parameters of linden trees.Under light shading(LS)treatment,Pn,Gs,Tr,and WUE levels can be significantly increased,while Pn,Gs,Tr,and WUE levels under moderate shading(MS)and severe shading(SS)treatments are less than control(CK).The LCP,LSP and AQY of the two types of lime trees all showed a downward trend,showing their adaptability to low light.At the same time,Tilia Rd showed a downward trend with the increase of shading degree.Both types of lime trees reached the maximum Pmax under light shading(LS)treatment.It can be seen from the above that in a shading environment,linden trees improve the use of weak light by reducing LCP,LSP,and Rd.(4)With the increase of shading treatment,the Fm,Fv/Fm,Fv/Fo,φPo,Ψo and φEo of the two types of lime trees increased,while φDo and DIo/RC decreased.It shows that linden tree has strong adaptability in low light environment.In order to adapt to the shading environment,normal growth is maintained by increasing the quantum ratio of electron transfer and reducing the quantum ratio of heat dissipation.(5)According to the results of principal component analysis,the comprehensive value F of each shading treatment is shown as LS>CK>MS>SS.Combined with principal component analysis and correlation analysis,4 photosynthetic rate(Pn),energy captured by unit reaction center for electron transfer(ETo/RC),leaf pigment(Chla+b),and light compensation point(LCP)are obtained.Physiological factors that have a major impact on seedlings,according to the analysis results of the affiliation of the four physiological factors,it is further obtained that the growth promotion effect of each shading condition on the seedlings is LS>CK>MS>SS.