Effects Of Shading And Light Restoration On Physiological And Photosynthetic Characteristics Of Schima Superba Seedlings

Schima superba Gardn.Et Champ.Is a common tree species in the subtropical region of China,and it is also an ideal pioneer and ecological fire protection tree species known at present.In order to explore the response mechanism of vegetative growth,photosynthesis,and physiological characteristics of Schima superba seedlings under different shade intensities,and to understand the photosynthesis,physiological changes,and light protection mechanism of Schima superba seedlings when they turn into natural light after shading,this project takes Schima superba annually Seedlings are the test objects.By artificially constructing a shading net room method,setting different light intensity gradients to carry out shading experiments(shading intensities are 100%,60%,40%,15%,5% of natural light,respectively)to simulate the wild In different light environments in actual forest stands,a pot experiment of Schima superba was carried out.Analysis of physiological and ecological characteristics of Schima superba seedling growth morphology,biomass accumulation and distribution,photosynthetic characteristics,antioxidant enzyme activity and chlorophyll fluorescence response to different light intensity environments;and photosynthesis parameters of Schima superba seedlings under natural light conditions after shading removal,Membrane lipid peroxidation products and chlorophyll fluorescence and other photosynthetic physiological characteristics changes.The aim is to explore the response mechanism of Schima superba seedlings to morphological plasticity and physiology and ecology in different light intensity environments during the early regeneration process,and to provide a theoretical basis for Schima superba cultivation and scientific guidance for the efficient cultivation and management of Schima superba plantation.The main findings are as follows:(1)After shade treatment,the plant height,ground diameter,leaf length,leaf width,leaf area,aboveground and underground biomass of Schima superba seedlings showed an increasing-decreasing trend with the increase of shading intensity,and were all at 85% The maximum value was reached under shading conditions;after shading treatment,the leaf and diameter distribution ratio of Schima superba seedlings increases continuously with the increase of shade intensity,while the root distribution ratio and rootroot ratio showed the opposite trend,moderate shade could promote the accumulation of aboveground biomass of Schima superba seedlings,and more resources were allocated to aboveground growth to enhance plant light capture and utilization efficiency in low light environments.(2)After shading treatment,with increasing shading intensity,net photosynthetic rate(Pn),transpiration rate(Tr)and stomatal conductance(Gs)of Schima superba seedlings all reached their maximum under 40%shading conditions.The change trend of intercellular CO2 concentration in Schima superba seedlings was the opposite,and it was the smallest under40% shading conditions;the water use efficiency(WUE)of Schima superba seedlings kept increasing with increasing shading intensity decreased,the difference between treatments was significant(P <0.05);initial fluorescence(F0)and maximum fluorescence(Fm)showed an increasing-decreasing trend with increasing shade intensity,and the maximum fluorescence yield(Fv / Fm)between different treatments showed a certain difference,and Schima superba seedlings exhibited significant light inhibition under 95% shading.(3)Superoxide dismutase(SOD)of Schima superba seedlings differed significantly among different treatments,and reached its maximum under85% shading conditions;shading treatment made the catalase(CAT)and malondialdehyde(MDA)of Schima superba less than CK,and its value showed a downward-increasing trend with the increase of shading intensity;meanwhile,shading treatments promoted Schima superba seedlings to increase the content of chlorophyll a,chlorophyll b,chlorophyll(a + b)and carotenoids(Car),by synthesizing a large number of photosynthetic pigments to ensure the absorption of light energy in Schima superba under weak light.(4)After shading was removed,the photosynthetic rate(Pn),transpiration rate(Tr),and stomatal conductance(Gs)of Schima superba seedlings began to rise slowly,while the intercellular CO2 concentration was opposite,showing a downward trend.Among them,the net photosynthetic rate of seedlings recovered the fastest after 40% shading treatment,and returned to CK level on the third day of shading removal,but only 40% shading treatment and 60% shading treatment recovered to10 days CK level.The transpiration rate of Schima superba under light recovery showed a downward trend and then an upward trend.60%shading treatment and 85% shading treatment returned to CK level on the10 th day after shading removal,but 40% shading treatment and 95%Shading treatment has not been restored.The stomatal conductance of seedlings of all treatments recovered to CK level on the 10 th day after shading removal.The change trend of intercellular CO2 concentration was contrary to the gas parameters.On the 10 th day of light recovery,only 95%of the shading treatment dropped to CK level,and the remaining treatment groups were still slightly higher than CK.(5)After restoring natural light,the PSⅡ electron transport activity Fm /F0 of Schima superba seedlings decreased first and then increased with time.The change trend of the maximum photochemical efficiency Fv / Fm was basically consistent with Fm / F0.95% of the shading treatments did not recover well.Fm / F0 and Fv / Fm only recovered to 50.6% and 63.5% of CK,which was lower than other treatments.Extreme shading made Schima superba seedlings recover from light Suffered from severe light damage.(6)After restoring natural light,the Car content of each shade group continued to rise,being 95% shade> 85% shade> 60% shade> 40% shade>CK.The non-photochemical quenching(NPQ)content of Schima superba seedlings began to rise after a short decrease,indicating that Schima superba seedlings could not quickly adapt to the rapidly changing light environment at the initial stage of shading removal,and as the number of days of recovery increased,The seedlings of Schima superba gradually adapt to the natural light environment,and their heat dissipation ability begins to recover.The MDA content of Schima superba seedlings was lower than that of CK in the shading stage.The MDA content of the 40%shading treatment continued to rise after light recovery and reached the CK level on the third day,but soon began to decline on the seventh day Until the 10 th day of light recovery,the MDA content of each treatment did not exceed the CK level.