Effects Of Shading On The Growth And Physiological Characteristics Of Cyclobalanopsis Gilva Seedlings

Cyclobalanopsis gilva is an evergreen tree belonging to the family Fagaceae.Studies have shown that the regeneration of understory seedlings is closely related to the light environment in the forest.In this study,one-year-old C.gilva seedlings were used as test materials,and 5 shading intensities were set,from low to high:no shading,30%,50%,70%,and 90%shading.Discuss the changing trend of C.gilva seedling growth and physiological indicators under different shading intensities.The aim is to determine the optimal light conditions for C.gilva seedlings,and to provide theoretical basis and practical guidance for the selection of light environment for scientific breeding and artificial intervention in understory seedling regeneration.The main research conclusions are as follows:(1)The analysis of morphological and structural indicators showed that the growth of ground diameter and seedling height increased first and then decreased with the increase of shading intensity.The highest shade at 50%is 2.63mm,15.68cm,and the lowest at 90%shade is 1.32mm,10.31cm.Stem,leaf biomass and total biomass show the same effect.It shows that 50%shading promotes the growth and development of C.gilva seedlings,while 90%shading causes its normal growth and development to be restricted.At the same time,C.gilva seedlings under the shading treatment tend to concentrate the biomass on the above-ground part to maximize the light resources.A series of leaf type indexes of leaf length,leaf circumference,leaf area and specific leaf area all decrease with the increase of shading intensity.A series of leaf anatomical structure indexes of fence tissue thickness,sponge tissue thickness,palisade-to-sea ratio,and tissue structure compactness showed the same change trend.(2)Analysis of photosynthetic indicators showed that the content of Chl a,Chl b,Chl t and Car all increased to varying degrees under shading treatment.The characteristic value of light response show different trends with the increase of shading intensity,and Pnmax first increases and then decreases with the increase of shading intensity.The maximum shading at 50%is 9.83 μmol·m-2·s-1 and the minimum at 90%shading is 4.95 μmol·m-2·s-1.With the increase of shading intensity,PLS gradually decreased,PLC first decreased and then increased,while Rd and AQY showed no significant difference between different treatments.The gas exchange parameters show a high degree of correlation in different months.Among them,Gs,Ci,Tr and Pn reached higher values at 30%and 50%in the early stage of shading,and reached higher values at the late stage of shading without shading.In different months,Y(Ⅱ),ETR,and qP all increased first and then decreased to the degree of shade deepening.They also reached the highest at 30%or 50%shade,and reduced to the lowest at 90%shade.(3)Physiological index analysis shows that the SS content and SP content in the early stage of shading accumulate in a large amount when 30%and 50%are shaded,and they reach the highest when there is no shade in the later stage.In different months,the content of Pro and MDA reached the highest at 90%shading.SOD and CAT play a protective and regulating effect on C.gilva seedlings in the early stage of shading,and POD in the late stage of shading.At the same time,the POD and CAT activities of 70%shading in the later stage of shading are greater than 90%shading.The nutrient content of leaves under shading treatment shows different trends.N,P,K content all reach the highest under 30%or 50%shade conditions,showing a certain synergistic effect.Ca content fluctuates significantly in different months,reaching the highest value in June and August without shading,and reaching the lowest value in July and September without shading.The Mg content reached the highest under 90%shading conditions except in August.In summary,under 50%shading conditions,C.gilva seedlings’ growth and development status and physiological regulation mechanisms are in the best state.In future seedling breeding and artificial intervention in understory seedling regeneration,attention should be paid to the choice of light environment,and 50%shading is the most suitable light condition for growth.