| Light is one of the basic factors for plant growth and development,which has regulation effects on plant photosynthesis,growth and development,morphogenesis,metabolism and gene expression.In order to explore and systematically reveal the most suitable light conditions for different growth periods and growth stages of plants we developed the device of light and temperature control system for plants under different lighting modes(DLMs)of LED and the hydroponic device for the bolt-resisting lettuce plant(Lactua sativa L.Italy),which was employed as research material grown under different light environment.Meanwhile,we determined the qualitative response mechanism of light to seed germination and seedling growth of lettuce via this system,which helped to find the most suitable light quality ratio in late experiments.Combing the conclusions on the effects of different lighting intervals on lettuce,we determined the factors and levels of different lighting modes for the orthogonal experimental design.The growth indexes and functional chemicals accumulation were analyzed and evaluated by the fuzzy comprehensive evaluation method.The most suitable lighting mode combinations of lettuce in growth and harvest periods were further analyzed by gray correlation analysis method.Finally,the most suitable lighting mode obtained previously was verified by experiments,and the most suitable lighting mode at different stages of lettuce was analyzed and determined.The primary study contents and results were summarized as follows.1 Development of plant culture system with different lighting modes of LEDIn order to investigate the relationship of the total amount and spectrum of light and the whole growth cycle of plant,we designed a plant culture system based on different lighting modes of LED,which mainly included the LED lamp design,control system of light and temperature,and the hydroponic device for plants.The results from the three-dimensional uniformity characteristics inside the system showed that not only did the developed plant culture system based on different lighting modes of LED have uniform lighting distribution,but the light environment factor and temperature parameters were easy to control.Not only can the light environment factor and temperature required for plant growth be flexibly set,but it can also provide a basis for exploring the most suitable lighting modes and regulation strategy of plants at different growth stages.2 Effects of different ratios of red to blue light on seed germination and seedling growth of lettuceThis study was conducted to determine the qualitative response mechanism of light to seed germination and seedling growth of lettuce,and to provide theoretical evidences for developing the most suitable lighting mode for the growth of lettuce at different stages.The effect of five light qualities,in which red to blue light ratios were set at 9R:1B,7R:3B,5R:5B,3R:7B,and 1R:9B,on seed germination and seedling growth of lettuce was investigated.Results showed that the seed germination and seedling growth rates under 7R:3B treatment were significantly greater than those under control treatment(fluorescence).Treatment of 3R:7B produced higher amount of photosynthetic pigments.A well-developed root system was observed under both 9R:1B and 7R:3B treatments.Significantly higher level of chlorophyll fluorescence of lettuce was detected under 7R:3B,5R:5B,and 3R:7B treatments,while the lower level of pigment content,chlorophyll fluorescence,the activity index of seeds,and root vigor was shown under 1R:9B treatment.Findings of our experiment indicated that red to blue light ratio at 7R:3B,5R:5B and 3R:7B could be used as the suitable light source in the future for studying the effects of different lighting modes on the growth of lettuce.3 Fuzzy comprehensive evaluation of the most suitable lighting mode for lettuce seedlingsFor a deeper understanding of the effect of different lighting modes on the growth and quality of lettuce in seedling period,the lighting conditions for lettuce plants were set by the orthogonal experimental design method,which was composed to the combination of red and blue light(7:3,5:5 and 3:7,respectively),photoperiod(12L/12D,16L/8D and 20L/4D,respectively,where L represents for light and D f r dark),and light intensity(100 μmol·m-2·s-1,150 μmol·m-2·s-1,200 μmol·m-2·s-1,respectively),and the growth parameters and functional chemicals were studied under these conditions.A total of 10 treatments including the fluorescent lamp one(CK,as a control)were used for the growth of lettuce seedlings and the results were analyzed and evaluated by the fuzzy comprehensive evaluation method.The results showed that the weights used for the fuzzy comprehensive evaluation method of plant height,stem diameter,hypocotyl length,fresh weight of the whole plant,chlorophyll,soluble sugar,soluble protein and nitrate were 0.1018,0.0466,0.0780,0.2736,0.1487,0.0548,0.0548,and 0.2418,respectively.Based on the above results,we concluded that the most suitable combination of lighting mode for lettuce seedling cultivation was the 5:5 for the ratio of red to blue light,20L/4D for photoperiod and 100 μmol·m-2·s-1 for light intensity.In addition,the use of analytic hierarchy process(AHP)had a good adaptability to the comprehensive evaluation of the cultivation effect of different lighting modes of lettuce.Moreover,the most suitable lighting mode was helpful to obtain the best lettuce seedlings in industrialized seedling production.4 Optimization of the light environment of lettuce in growth period based on gray relational analysisIn order to ensure the annual supply of facility lettuce,the effects of different lighting modes on the growth characteristics of lettuce in growth period under artificial climatic conditions were studied to determine the most suitable light environment for lettuce growth.The influence of the light settings on the growth,photosynthetic pigment content and quality of lettuce in growth period was analyzed by using the gray relational analysis method.Results showed that compared with other light environmental conditions,treatment with the ratio of red to blue 7:3,photoperiod 20L/4D and light intensity 150 μmol·m-2·s-1 was more conducive to the accumulation of photosynthetic pigments.The combination with the ratio of red to blue 3:7 was more conducive to protein synthesis than other treatments.Treatment T3 with the ratio of red to blue 7:3,photoperiod 20L/4D and light intensity 200μmol·m-2·s-1 had lower nitrate content and higher soluble sugar than other light treatments.From the results obtained in our experiments,we could conclude that the most influential factor on growth and chemical accumulation of lettuce in growth period was light intensity,followed by the light quality and the least was photoperiod.The most suitable combination of light was as follows:the ratio of red to blue 7:3,light intensity 200 μmol·m-2·s-1,and photoperiod 20L/4D.These results would provide some references for the settings of the best light environment for lettuce and some technological support for the design of LED(Light-emitting diode)lamps in the field of plant-lightings.5 Optimization of the light environment of lettuce in harvest period based on gray relational analysisThe appropriate adjustments for light environment in harvest period are not only conducive to save energy,but effectively promote the yield and quality of plants.The gray relational analysis method was used to systematically analyze and compare the growth and nutritional quality of the lettuce in harvest period.Results showed the inconsistence of response of different photobiological indicators,such as SPAD and chlorophyll(a+b)content,or asynchrony(such as soluble sugar)to light environment.Not all plant morphological and nutritional indicators changed in the same direction,instead,they showed a discrete response.The morphological indexes were better under the 7R:3B(ratio of red to blue light)treatments and treatment T9 with the ratio of red to blue 3:7,photoperiod 20L/4D and light intensity 150 μmol·m-2·s-1 was more conducive to the accumulation of photosynthetic pigments.The combination with the ratio of red to blue 5:5 and 3:7 were more conducive to protein synthesis than other treatments.Treatment T3 with the ratio of red to blue 7:3,photoperiod 20L/4D and light intensity 200 μmol·m-2·s-1 had lower nitrate content.Soluble sugar content under treatments T3,T6(the ratio of red to blue 5:5,photoperiod 20L/4D and light intensity 100,μmol·m-2·s-1),and T9 were higher.Based on the gray relational analysis and the orthogonal experiment optimization selection,we can conclude that the most influential factor on growth and chemical accumulation of lettuce in harvest period was photoperiod,followed by light intensity,and the least was light quality.The most suitable combination of light was as follows:the ratio of red to blue 5:5,light intensity 200 μmol·m-2·s-1,and photoperiod 20 h.6 Verification of the most suitable lighting mode for the lettuce at growth stageIn order to determine the most suitable lighting modes for lettuce growth at each stage,we explored and verified the effects to the changes of different factors around the most suitable lighting modes of lettuce in growth period on the growth,nutritional quality and gene expression of lettuce based on the obtained most suitable modes.The results showed that increasing the day light integral(DLI)of red light could increase the growth and biomass of lettuce,but reduce the antioxidant enzyme activity and nutritional quality of lettuce under the same ratios of red to blue light.Treatments with higher portion of blue light were beneficial to reduce the nitrate content and promote the synthesis of flavonoids.Increasing light intensity or prolonging photoperiod could positively affect the morphogenesis of lettuce at growth stage,but inhibite the synthesis of pigment and the enzyme expression of CAT,SOD and increase the accumulation of nitrate,which was not conducive to the accumulation of pigment content,soluble sugar and soluble protein in lettuce leaves.Under the same light intensity and photoperiod respectively,treatments with higher portion of red light could increase the enzyme activity of CAT in lettuce plants,promote ’the accumulation of soluble sugar and soluble protein,but decrease the activity of SOD and MDA content.The 7:3 ratio had a better effect on the promotion of flavonoids.The results of qRT-PCR showed that the gene expression of NR and NIR was highest under Y6 with the ratio of red to blue 7:3,photoperiod 20L/4D and light intensity 200μmol·m-2·s-1,which was consistent with the lowest nitrate content in this treatment.It could increase the expression level of flavonoid synthesis-related functional genes and promote the synthesis of flavonoids by adding a certain amount of blue light among different lighting modes.The results of comprehensive power and energy consumption of light source indicated that both consumption was the lowest under Y6 treatment,which could reduce the operating cost in actual production and show advantages of energy saving and high efficiency in reducing energy consumption and improving nutritional quality.7 Analysis of the most suitable lighting modes for the lettuce at different stagesIn order to obtain the most suitable lighting conditions for lettuce at different stages of growth,the results from different periods were used to determine the most suitable lighting modes by further analysis and comparison.Results showed that the most suitable lighting mode for lettuce grown from transplant to seedling stage was as follows:the ratio of red to blue 5:5,photoperiod 16L/8D,and light intensity 200μmol·m-2·s-1,same as the result from growth to harvest Stage.The most suitable lighting mode from seedling to growth stage was as follows:the ratio of red to blue 7:3,photoperiod 20L/4D,and light intensity 150 μmol·m-2·s-1.Compared with the results from the study in previous chapters for the most suitable lighting modes for the lettuce in different periods,it was found that the most suitable light quality was the same between different periods and different stages,but the most suitable photoperiod and light intensity were different.In addition,the total DLI for different periods was maintained at 14.40 mol·m-2·d-1,but the highest DLI was only 11.52 mol·m-2·d-1 for different stages.The results indicated that it was more conducive to reducing energy consumption and more targeted to study the most suitable lighting modes for lettuce at different stages compared with the study for different periods. |
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