Effects Of Different Light Quality And Light Intensity On Growth And Development Of Gleditsia Sinensis Seedlings

Solar radiation is the energy source on the earth,and sunshine is closely related to solar radiation.The sunshine duration in Guizhou province is high in the west and low in the east,and the distribution of sunshine intensity is not uniform.The quality of Gleditsia sinensis seedlings cultivated in different areas is very different,so it is of great significance to study the growth of Gleditsia sinensis seedlings by light.In this study,Gleditsia sinensis seedlings were used as experimental materials to study the effects of different light environment on the growth and development of Gleditsia sinensis seedlings,and to discuss the physiological mechanism that affects the growth of Gleditsia sinensis seedlings and how to promote seedling growth by changing the light environment.The main research results are as follows:L3(200μmol·m^-2·s^-1)light intensity was beneficial to stem thickening and accumulation of dry matter,chlorophyll,carotenoid and soluble sugar,significantly increased leaf area and leaf thickness of Gleditsia sinensis seedlings,and significantly decreased MDA accumulation.L1(50μmol·m^-2·s^-1)light intensity resulted in lamellar separation of stromal thylakoid,resulting in decreased accumulation of photosynthetic pigments and increased initial fluorescence F₀.The maximum fluorescence F_m,the maximum photochemical efficiency of PSII F_v/F_m,the effective photosynthetic quantum yield F_v’/F_m’,the actual photosynthetic quantum yield Y（Ⅱ）and the maximum electron transfer rate ETR_maxof PSⅡdecreased.The contents of starch,soluble protein and soluble sugar and the activities of POD and SOD were significantly lower than L3.In L2(100μmol·m^-2·s^-1)treatment,the leaf structure compactness（CTR）was significantly higher than L1 and L3,the stomata length was significantly lower than L1 and L3,and Fv’/Fm’and Y（Ⅱ）were always at a high level.The results showed that the light intensity of 200μmol·m^-2·s^-1was suitable for the growth of Gleditsia sinensis seedlings.When the light intensity was lower than 50μmol·m^-2·s^-1,the photosynthetic organ structure was destroyed and the photosynthetic efficiency was reduced,which was not conducive to the growth of Gleditsia sinensis seedlings.Red light decreased stem thickening and growth,yellow light decreased seedling height and increased specific leaf weight,red and yellow light were not conducive to the increase of chlorophyll and carotenoid content but beneficial to the accumulation of total nitrogen content.Blue light irradiation is beneficial to increase soluble protein and total nitrogen content.Red light decreased CAT activity and SOD activity of Gleditsia sinensis leaves,and increased MDA content.Adding the same proportion of blue light into red light could improve CAT and SOD activities and reduce MDA content.RB2 was beneficial to the accumulation of starch and sucrose and the increase of SPS activity,while RB was beneficial to the increase of seedling index,root shoot ratio,the accumulation of total sugar and soluble sugar and the increase of NR activity.The results showed that monochromic light had a positive effect on Gleditsia sinensis seedlings,but was not conducive to the overall development of Gleditsia sinensis seedlings.Mixed light quality could promote the overall development of Gleditsia sinensis seedlings and improve the carbon and nitrogen metabolism of seedlings.Compared with white light,red light decreased seedling strength index and stem diameter,while yellow light decreased seedling height.Both red and yellow light were not conducive to the increase of chlorophyll and carotenoid content,but was beneficial to the accumulation of total nitrogen content.Blue light irradiation was beneficial to increase leaf thickness,palisades tissue thickness,initial slopeα,maximum electron transfer rate ETR_max,high light tolerance I_k,maximum conversion efficiency F_v/F_mof PSⅡ,potential activity F_v/F₀of PSⅡ,soluble protein content and total nitrogen content.The combination of red and blue light（RB,RB2）was beneficial to the increase of leaf thickness and palisade tissue thickness,and the accumulation of starch content,total sugar content,soluble sugar content and sucrose content,while the combination of yellow and blue light（YB,YB2）was beneficial to the increase of sponge tissue thickness of gleacia sinensis leaves.Red-blue combined light（RB）and yellow-blue combined light（YB）were beneficial to the increase of initial slopeα,maximum electron transfer rate ETR_max,high light tolerance I_kand nitrate reductase activity.With the increase of blue light ratio,the thickness of palisade tissue and palisade sea ratio increased,the content of carotenoids increased,sucrose content,sucrose synthase and sucrose phosphate synthase activities increased.The ratio of height to aspect,ETR_max,I_k,F₀and F_vdecreased significantly,and the contents of total nitrogen,starch and sugar and nitrate reductase activity decreased significantly.The results showed that red light was not conducive to the growth of Gleditsia sinensis seedlings,and blue light had a positive regulating effect on the growth of Gleditsia sinensis seedlings.Red blue light was beneficial to the increase of seedling height and yellow blue light was beneficial to the growth of stem diameter and seedling strength index of Gleditsia sinensis seedlings.LED irradiation for 30 days was beneficial to the accumulation of soluble sugar content and leaf nitrogen content,and inhibited photosynthetic efficiency and antioxidant enzyme activity.The contents of chlorophyll,carotenoid,starch and soluble sugar in Gleditsia sinensis leaves increased after LED irradiation for 60 days,while MDA content decreased.Yellow blue light was better than red blue light.LED irradiation for 90 d was beneficial to the improvement of photosynthetic efficiency of Gleditsia sinensis seedlings,red blue light was better than yellow blue light,but it was not beneficial to the growth of stem diameter,seedling index and nutrient accumulation.The results showed that LED illumination time was not the main factor affecting seedling growth,and the growth of Gleditsia sinensis seedlings was affected by both illumination time and quality.