| Plant factory is an efficient agriculture system which can obtain year-round production of crops through environmental of high precision in the facility. It has many advantages, such as:do not affected by natural condition; can gain a high yield per unit area; high utilization of land resources; can produce clean and safe products and so on, which is considered to be an vital method to deal with the population growth, lack of resources, environmental pollution, food safety and other issues in the future. Nutrient solution management and light environment regulation are two key technologies to overcome the bottleneck of production system of plant factory:high operating cost and high energy consumption. The suitable nitrogen supply and light is not only the guarantee of high yield and quality of vegetable production, but also affect the efficiency of the resources and energy utilization as well as application prospect of plant factory. Previous study always focus on either the light or the nitrogen supply, however, there were few reports focusing on the effect of the interaction of nitrogen nutrition and light on the biomass and quality of vegetables in the plant factory. Therefore, the study is intended to study the effect of the interaction between different nitrogen supply and light (quality or intensity), of pre-harvest nitrogen nutrition and light control on the biomass, nutrition and antioxidant quality, as well as of the light on the physiological mechanism of nitrate accumulation on aeroponic Lettuce (Lactuca sativa L.), which would provide theoretical basis for the management of nitrogen nutrition and control of light of vegetables growing in the plant factory. The main results are as follows:1. The effects of the interaction of different nitrogen supply (4,8 and 16 mmol/L) and light quality (red, blue, red and blue, white) on the yield, photosynthesis and nutrition and antioxidant quality of aeroponic Lettuce was studied. The results show that under the same light quality, with the nitrogen supply increase from 4 mmol/L to 8 mmol/L, aeroponics lettuce biomass and net photosynthesis photosynthetic rate increased significantly, however, when under the 16 mmol/L, its biomass and net photosynthesis photosynthetic rate decreased significantly and nitrate content significantly increased. With the increasement of nitrogen supply, the soluble sugar content decreased, and the soluble protein content increased significantly, and both of them had a high level under the 8 mmol/L. With the increasement of nitrogen supply, aeroponics lettuce antioxidants (glutathione, total phenolics and flavonoids) content and antioxidant activity (DPPH radical scavenging rate, FRAP values) were decreased significantly, but the antioxidant accumulation reached the maximum under the 8 mmol/L. When under the same nitrogen supply, aeroponics lettuce biomass, nitrogen content and net light synthetic rate is the highest, gain a relatively high level of soluble sugar, soluble protein, antioxidant content and accumulation, while the nitrate content stay at a low level. So, use red and blue light as light source,8 mmol/L as nitrogen supply can meet the demand of nitrogen and light for aeroponics lettuce, to maintain a high growth rate and biomass, higher nutritional and antioxidant activity at the same time.2. The effects of the interaction of different nitrogen supply (4,8 and 16 mmol/L) and light intensity (100 μmol·m-2·s-1,200 μmol·m-2·s-1,300 μmol·m-2·s-1,400 μmol·m-2·s-1, use LED R&B as light source) on the yield, photosynthesis and nutrition and antioxidant quality of aeroponic Lettuce was studied. The results show that under the same light intensity, with the increasement of nitrogen supply, aeroponic Lettuce fresh and dry weight, net photosynthetic rate showed increased first and then decreased, all of them are highest under the 8 mmol/L. With the nitrogen supply increase from 4 mmol/L to 8 mmol/L, aeroponics lettuce nitrate and soluble protein content increased significantly, soluble sugar decreased slightly, to go on increase the nitrogen supply, aeroponic Lettuce nitrate and soluble protein content continues to rise, and soluble sugar content significantly decreased. With the increasement of nitrogen supply, the content of antioxidant and antioxidant activity of the aeroponic Lettuce were significantly decreased, but the accumulation of antioxidant had no significant difference between 4 mmol/L and 8 mmol/L. Under the same nitrogen supply, when light intensity increase from 100 μmol·m-2·s-1 to 300 μmol·m-2·s-1, significantly increase was found on the biomass, soluble sugar, soluble protein and total phenolic content, antioxidant accumulation and antioxidant activity of aeroponic Lettuce, the glutathione and flavonoid content showed a trend of increase, the nitrogen nutrition status was improved. Continue to increase the light intensity to 400 μmol·m-2·s-1, aeroponic Lettuce biomass, glutathione, total phenolics, flavonoid content decreased slightly, although the total nitrogen, net photosynthetic rate, soluble sugar content is slightly increase, all of them did not reach the significant level. The nitrate content of aeroponic Lettuce decreased with the increase of the light intensity, while there are no significant difference between the light intensity of 300 μmol·m-2·s-1 and 400 μmol·m-2·s-1. As a result, considering the appearance, yield, nitrogen nutritional status, nutritional quality and production cost factors, choose light intensity of 300 umol·m-2·s-1 with LED R&B, combination with 8 mmol/L nitrogen supply is suitable for aeroponic lettuce in plant factory.3. We studied the effects of reducing light intensity one week priorto harvest on the yield, nutrition and antioxidant qualities of aeroponic lettuce in the appropriate level of nitrogen supply. The results showed that reducing light intensity to 200 μmol·m-2·s-1 one week before harvest made no difference in the biomass, net photosynthetic rate, nitrate and soluble sugar content of aeroponic lettuce, but significantly reduced soluble protein, increased Leaf SPAD value, antioxidant contents and antioxidant activity, obviously reduced energy consumption as well as saved cost, which were different from sustaining light intensity of 300 μmol·m-2·s-1. Further reducing light intensity could lead to significant reduction in yield, net photosynthetic rate, soluble sugar and soluble protein content, as well as nitrate accumulation in lettuce. As we can see, reducing light intensity to 200 μmol·m-2·s-1 before the harvest does not affect the yield and antioxidant nutrients of lettuce. Therefore, it is effective in reducing energy consumption and cost in the spray culture system of the plant factory.4. We carried out a research about effect of light intensity (200 μmol·m-2·s-1,300 μmol·m-2·s-1,400 μmol·m-2·s-1and light quality (red, blue, red and blue, white) on short term absorption of nitrate nitrogen and accumulation of aeroponic lettuce. The results showed that different light intensity and light quality only influenced rate Vmax of root absorbing nitrate nitrogen, but did not change its affinity km for nitrate nitrogen. In the light intensity of 300 μmol·m-2·s-1, the nitrate absorption rate of lettuce reached to maximum, nitrate reductase activity reached to the highest, and concentration levels of nitrate within lettuce in the spray culture were relative low. In the blue light, the nitrate absorption rate of aeroponic lettuce reached to the maximum, followed by red and blue light. In the red light, nitrate reductase activity reached the highest, followed by red and blue light. Concentration levels of nitrate within aeroponic lettuce reached to the highest in the red light, followed by red and blue light, white light and blue light. To sum up, the light environment can control concentration levels of nitrate within aeroponic lettuce through impacting the absorption rate of nitrate nitrogen and nitrate reductase activity regulation of lettuce, which is appropriate in red and blue light with light intensity of 300 μmol·m-2·s-1. |
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