Effect Of Different LED Supplementary Lighting On Tomato And Cucumber Seedlings In Solar Greenhouse

In the production of vegetable seedling in northern China,the problem of weak and low light caused by seasonal factors and cold-proof measures is common in winter and spring.In recent years,a large number of studies have shown that LED light supplementation on vegetable seedlings can improve their growth.In this study,the tomato(Lycopersicon esculentum Mill.)variety 'Liaoyuan Dooli' and the cucumber(Cucumis sativus L.)variety'winner' were used.The effects of LED red light(R),blue light(B)and green light(G)on seedling growth were evaluated.In addition,these three kinds of light were combined to form combined light R9B1(9:1,the proportion of the number of lights),R8B2,R7B3,R9G1,R8B1G1,and R7B2G1,and their delayed supplement illumination effect on tomato and cucumber seedlings were analysed.The main findings were as follows:1.The results of delayed supplementary lighting showed that red and blue light could improve stem diameter,whole plant fresh and dry weight,leaf area,chlorophyll content,net photosynthetic rate of tomato seedlings,and significantly increased root length and root surface area of tomato seedlings.as well as it could reduce plant height and promote dry matter accumulation of tomato seedlings to a certain extent.In the green light treatment group,the root distribution rate of tomato seedlings were significantly improved,and the transpiration rate increased.The results of LED combination light showed that it was benificial to promote the growth of tomato seedlings,which could significantly improve the morphological indexes of seedlings such as stem diameter,whole plant fresh and dry weight,and seedling index.Physiological and biochemical indicators such as photosynthetic efficiency,chlorophyll content,soluble sugar content,root activity and stress resistance were significantly improved.R7B2G1 was the best LED light combination on tomato seedlings.The delayed supplement of LED combined light at different seedling period discovered that the use of LED red,blue and green combined light on tomato seedlings in the first true leaf exposure period(T1)could significantly improve the growth morphology,seedling index and chlorophyll content,promote photosynthesis,improve root morphology,raise root vigor and stress resistance.Compared with the control group,the application of LED combined light on seedlings of tomato in the second true leaf exposure period(T2)achieved good results,thought not significant.From the perspective of overall growth morphology,the morphological and physiological indexes of tomato seedlings in low light treatment group(Td)were lower than that of the control group,indicating that weak light environment is not conducive to the growth of seedlings.The photosynthetic rate and transpiration rate of tomato seedlings at night with R7B2G1 reached the maximum at 3 hours,and the stomatal conductance also increased significantly.The net photosynthetic rate after light supplement for 4 hours was still greater than 1 hour.Therefore,the optimal time for delayed supplementary lighting of tomato seedlings at night was 4 hours.2.The results of delayed supplementary lighting showed that red and blue light couldimprove stem diameter,whole plant fresh and dry weight,leaf area,chlorophyll content,net photosynthetic rate of cucumber seedlings,and significantly increased root length and root surface area of cucumber seedlings.as well as it could reduce plant height to a certain extent.In the green light treatment group,the fresh dry weight,true leaf area and chlorophyll content of cucumber seedlings were significantly improved,and the transpiration rate of seedlings increased.The results of LED combination light on cucumber seedlings showed that it was benificial to promote the growth,which could significantly improve the stem diameter,whole plant fresh and dry weight,seedling index,and photosynthetic efficiency,chlorophyll content,soluble sugar content,root activity,stress resistance were significantly improved.R8B1G1 was the best LED light combination on cucumber seedlings.The delayed supplement of LED combined light at different seedling period of cucumber seedlings discovered that the use of LED red,blue and green combined light in the first true leaf exposure period(T1)could significantly improve the growth morphology,seedling index and chlorophyll content,promote photosynthesis,improve root morphology,raise root vigor and stress resistance.Compared with the control group,the light-filling treatment at T2 period significantly increased the seedling index and G value of cucumber seedlings.From the perspective of overall growth morphology,the morphological and physiological indexes of cucumber seedlings in low light treatment group(Td)were lower than that of the control group.The photosynthetic metrics of cucumber seedlings with the complement of R8B1G1 at night could achieve the desired state between 2 hours and 3 hours,but photosynthesis begined to decrease after 3 hours.Therefore,the optimal time for delayed supplementary lighting of cucumber seedlings was 3 hours.3.The net photosynthetic rate of the delayed supplementary lighting at night were lower than the day.The morphological indexes and seedling index of the seedlings in the nighttime light-filling were significantly improved.It showed that the LED combined light intensity in this study was stronger than the real light compensation point of seedlings,and the nighttime delayed light supplement was beneficial to the material accumulation of seedlings,thereby promoting its growth.In summary,the delayed supplementary lighting of LED red,blue and green combined light on the tomato and cucumber seedlings(especially in the T1 phase)could effectively improve the growth morphology and refine the physiological characteristics of the seedlings to achieve better growth.