| Populus is one of the main afforestation species of plantations in China,it has the characteristics of fast-growing,high-quality,wide ecological adaptation and so on.Populus has important ecological and economic value.In recent years,more and more traits are genetically improved,and the purpose is to cultivate more excellent varieties with higher speed,high quality and good resistance.The theoretical study on the high-efficiency poplar hybrid clones has certain guiding significance for the screening of high-efficiency clones in seedling stage.In this study,six P.×euramericans hybrid clones with different genotypes were selected.3 light intensity levels with a shading net were setted,there were CK?100%natural light intensity?,L1?55%natural light intensity?,and L2?20%natural light intensity?.In order to study the differences in response to growth and photosynthetic physiological characteristics of P.×euramericans,we compared and analyzed the indicators of P.×euramericans clones under different light intensity treatments.The indicators included height and rice diameter growth,leaf morphology and anatomical characteristics,element content,photosynthetic physiological characteristics and physiological and biochemical indexes.It is hope that it can provide a theoretical basis for the rapid selection of high-efficiency and high-efficiency varieties in the poplar stage in P.×euramericans.The main results of this experiment are as follows:?1?With the decrease of light intensity,seedling height,stem growth,leaf number,palisade tissue thickness,spongy tissue thickness and stomatal frequency of leaf surface decreased,while leaf water content,specific leaf area,potassium,calcium and magnesium increased.The contents of carbon and phosphorus in leaves of P.×euramericans clones treated with excessive shading?L2?were lower than those treated with normal light?CK?,and the content of nitrogen was the highest under L1 treatment.?2?Proper reduction of light intensity was helpful to improve the net photosynthetic rate of P.×euramericans clones.Under L2 treatment,the Fv/F0 and Fv/Fm of clones decreased significantly.During T1 period,the net photosynthetic rate of clones had the minimum value under L2 treatment,and the intracellular carbon dioxide concentration had the maximum value under L2 treatment.The stomatal conductance and transpiration rate of each clone showed different trends with the decrease of light intensity.The net photosynthetic rate of 11-36-26 was smaller under three light intensity treatments.The Fv/F0 and Fv/Fm of 11-21-8,11-26-4,11-32-1,11-36-26 clones decreased with the decrease of light intensity.Except for clone 11-36-26,the net photosynthetic rate of clones treated with L1 and L2 increased relatively after returning to normal natural light intensity.?3?With the decrease of light intensity,the total chlorophyll content,cell membrane permeability and MDA content of P.×euramericans clones showed an increasing trend,while the content of organic osmotic regulatory substances decreased.The change trend of the activity of POD and SOD was different among different light intensity treatments.The POD activity and SOD activity of 11-26-8,11-26-9,11-32-1 and 11-36-26 were the lowest under L2 treatment,and the POD activities of 11-21-8 and 11-26-4 were still high under L2 treatment,which could effectively reduce the oxidative damage of cell membrane.?4?The score of principal component comprehensive evaluation of clone decreased gradually with the weakening of light intensity.According to the comprehensive evaluation of clones by using the value of membership function,the ranking of 11-26-9 clones increased gradually with the decrease of light intensity,11-26-8 clones ranked 1st under CK treatment,11-36-26 clones ranked lower under the three treatments,and 11-21-8 clones ranked higher under all three treatments. |
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