| Plant factory is a kind of integrated efficient agricultural system that allows people controlling water and fertilizerprecisely. And it provides an effective means to controlling vegetable providing environment. However, high nitrogen level nutrient solution will cause quality problem of leafy vegetable such as high nitrate content, low ascorbic acid content and low soluble sugar content. And these problems, to some degree, reduce the market competitiveness of vegetable planted in plant factory, and hinder the popularizing of plant factory as well. Therefore, it is necessary to explore new method that applies to plant factory to improve quality of leafy vegetable. The cultivar of leafy vegetable is various, so the environment requirement of leafy vegetable is multiple and discrepant. Thus, studying the suitable planting environment of different cultivar leafy vegetable specifically is of great importance. In this study, red lettuce, purple lettuce and greenlettuce were hydroponically cultivated and the difference of their response to nitrogen nutrition conditions, light environment and the combination of nitrogen form and light environment were studied to analyze nitrogen nutrition condition and light environmental demand difference of the three cultivars. The main results and conclusions are as follows:1. Yield of the three kinds of lettuce was influenced by nitrogen level significantly, it was greater when the nitrogen concentration was 10mmol/L(N10) compared with that when the when the nitrogen concentration was 5mmol/L(N5). Shoot dry weight of green lettuce and red lettuce was higher under treatment N10, while purple lettuce was higher under treatment N5. Nitrogen level didn’t affect nutritional quality of the three kinds of lettuce greatly. However, biomass and nutritional quality of the three kinds of lettuce were significantly affected by nitrogen form. Shoot fresh weight, shoot dry weight and root shoot ratioof the three kinds of lettuce were greater under treatment combination of 5mmol/Lnitrate nitrogen and 5mmol/Lammonium nitrogen(N5+A5) compared with treatment of 10mmol/Lnitrate nitrogen only(N10+A0). Total phenols of green lettuce and red lettuce were slightly higher under N10+A0than N5+A5. Ascorbic acid content of green lettuce was relatively high under treatment N10+A0, while that of red lettuce and purple lettuce didn’t change much with the altering of nitrogen form. Nitrogen form didn’t affectanthocyanin content of the three kinds of lettuce.2. Yield and quality of the three kinds of lettuce differed greatly under homogeneous light and combination of red and blue light of different ratio. Shoot fresh weight of the three kinds of lettuce got the highest under white light or combination of red and blue light, and shoot dry weight got highest under combination of red and blue light. The three kinds of lettuce got the highest total phenols content under white light or combination of red and blue light, and got the lowest flavonoid content and anthocyanin content under red light, while got the highest anthocyanin content under combination of red and blue light. Soluble sugar contents of purple lettuce and red lettuce got highest under combination of red and blue light and got lowest under white light, while green lettuce respondedoppositely. The three kinds of lettuce under treatment of red and blue light under ratio 1:1 got the largest biomass. And totalphenols content and anthocyanin content of the three kinds of lettuce got the highest under treatment of red and blue light under ratio 1:2.3. Yield of three kinds of lettuce was mainly affected by photoperiod and the nutritional quality was primarily influenced by combined action of light quality and photoperiod. Extension of lighting period enlarged the leaf area and improved the shoot fresh weight of the three kinds of lettuce, while the shoot fresh weight didn’t change much when the light quality altered. The effects of light quality and photoperiod on phenol and flavonoid relative contents of green lettuce and red lettuce differed when the light quality varied, while phenol relative contents of purple lettuce improved greatly with the extension of lighting period.Anthocyanin relative contents of green lettuce and purple lettuce were not affected by the change of light quality and photoperiod significantly.Nonetheless, anthocyanin relative contents of red lettuce responded to the change of photoperiod diversely with the change of light quality.Ascorbic acid content of three kinds of lettuce decreased significantly with the lengthening of lighting period.Soluble protein contents of green lettuce and red lettuce responded to the change of photoperiod differently with the variation of light quality, and their response to light quality also affected by the change of photoperiod. However, soluble protein content of purple lettuce was affected by neither light quality nor photoperiod.4. Purple lettuce were grown hydroponically under six different nitrogen nutrition conditions for 25 d insolar greenhouse, and then treated with continuous lighting for 72 h before harvesting, to study the changes in contents of nutrient and analyze the effects of nitrogen nutrition conditions on the changes. Results showed that the shoot dry weight and root dry weight of all six nitrogen nutrition conditions were significantly improved under 72 h continuous lighting. The relative contents of total phenols and flavonoid of different nitrogen nutrition conditions turned significantly different after treated with continuous lighting. The lighting treatment reduced the nitrate content of leaf blades and leaves of all six nitrogen nutrition conditions remarkably. The soluble sugar contents and soluble protein content of all six different nitrogen nutrition conditions improved notably after continuous lighting treating.5.Purple lettuce and green lettuce were hydroponically cultivated in the culturing room to investigate the influence of light quality and continuous lighting on their growth and nutritional quality. The results showed that the shoot fresh weight and root fresh weight of the two kinds of lettuce improved under treatment of continuous lighting.Phenol and flavonoid relative contents of purple lettuce and green lettuce responded to continuous lighting treatment differently with the variation of light quality.The ascorbic acid content of purple lettuce lessened greatly under continuous lighting.The influence of continuous lighting on soluble sugar content of green lettucediffered with the change of light quality. Under the same light quality, soluble protein contents of green lettuce dropped under treatment of continuous lighting. |
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