Photosynthetic Characteristics And Leaf Anatomical Structure Of Five Precious Tree Species Under Shading Condition

The distribution,growth and live of plants were shifted by its response under dynamic sunlight environment.We determined the responds of seeding including photosynthetic fluorescence characteristics,leaf anatomical structure and growth siduation under four simulated sunlight conditions(full sunlight,30%,50%,70%shading).Meanwhile,the principal component analysis and membership function method were used to evaluate the shade-tolerance comprehensively for five valuable tree species including Phoebe bournei,Cyclobalanopsis gilva,Zelkova serrata,Cinnamomum camphora and Choerospondias axillaris.Such results could provide a guide of efficient cultivation and tree species deploying in mixed plantation.The main results as follows:1.Shading significantly affected the daily variation characteristics of plant seedling consisting of net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr)and intercellular CO2 concentration(Ci).Under full sunlight treatment in summer,the variety of Pn could be described by a bimodal curve,indicated that the ’midday depression’phenomenon were improved by the moderate shade.Under 30%shading treatment,the Pn of Cyclobalanopsis gilva and Cinnamomum camphora were higher than full sunlight treatment,which illustrated that moderate shading improved their Pn.With the increase of shading time,the adaptability of Phoebe bournei was enhanced,while the tendency of Zelkova serrata and Choerospondias axillaris were contrary.Under 70%shading treatment,the Pn of seedlings were decreased significantly,which was similar with the Gs and Tr,while the Ci had an opposite tendency.2.With a decrease of light,the apparent quantum yield(AQY)of seedlings had different amplitude increases in summer,meanwhile the light compensation point(LCP),the light saturation point(LSP)and the dark respiration rate(Rd)were decreased.The maximum net photosynthetic rate(Pnmax)of Phoebe bournei,Zelkova serrata and Choerospondias axillaris were decreased in shading treatments,while increased of Cyclobalanopsis gilva and Cinnamomum camphora under 30%shading treatment.In addition,the chlorophyll fluorescence parameters of seedlings were consistent with the photosynthetic capacity.The quantum yield(Y(Ⅱ))and the apparent photosynthetic electron transport rate(ETR)of Phoebe bournei,Cyclobalanopsis gilva and Cinnamomum camphora under moderate shading were not significantly different from those of full sunlight,while Zelkova serrata and Choerospondias axillaris were opposite,and their Y(Ⅱ)and ETR decreased significantly.Meanwhile,the decrease of photochemical quenching coefficient(qP)under shading were increased in September and the non-photochemical quenching coefficient(qN)were increased,which illustrated that with the increase of shading time,the ratio of light energy for heat dissipation increases.3.Under shading treatments,the thickness of leaves were decreased,the palisade tissue cells became shorter,the intercellular space were increased,the ratio of palisade tissue to sponge tissue were decreased,and the tissue structure porosity were increased.The more obvious the above changes with decreasing light intensity.In addition,the stomatal density of seeglings were smaller compared with the control.4.With a decrease of light,the chlorophyll content and leaf area of seedlings were increased,whlile the chlorophyll a/b ratio of seedlings were decreased.The seedlings showed different growth strategies in low light environments.The plant height of Zelkova serrata and Choerospondias axillaris increased continuously under shading treatment,while that of Phoebe bournei,Cyclobalanopsis gilva and Choerospondias axillaris increased relatively slowly.Meanwhile,Zelkova serrata,Choerospondias axillaris and Cinnamomum camphora distribute more biomass to leaves by significantly reducing the biomass of underground part in low light environments,so as to obtain more light energy.However,there was no significant difference between the ratio of stem and leaf biomass of Phoebe bournei and Cyclobalanopsis gilva under moderate shading and full sunlight,indicating that the plasticity of seedling biomass and its distribution characteristics were relatively low.5.The principal component analysis and subordinate function method showed that Phoebe bournei,Cyclobalanopsis gilva and Cinnamomum camphora showed good adaptability under moderate(30%and 50%)shading treatments,while Zelkova serrata and Choerospondias axillaris showed relatively poor adaptability to shading environments.In summary,Phoebe bournei,Cyclobalanopsis gilva and Cinnamomum camphora have higher shade-tolerance.These three tree species can be moderately shaded during the seedling stage.When replanting under the forest,care should be taken to control the shade of the stand.Zelkova serrata and Choerospondias axillaris show certain light-loving properties,and their adaptability to weak light environment is relatively poor.In the subsequent cultivation process,sufficient light should be ensured.