| Lettuce is a typical leaf vegetable, and there were few reports about the effect of day temperature, night temperature and photoperiod on lettuce. In this study, the effects of different day and night temperature and photoperiod treatments on the growth, quality of lettuce (cv. Lvling) were investigated. The study was made up of four parts: different day temperature treatments, different night temperature treatments, different photoperiod treatments, and primary research of growth modeling.1. The effects of three different day temperatures(20℃/15℃, 5℃/15℃and 30℃/15℃)on the growth and quality of lettuce were investigated. The results showed that leaf number, shoot fresh and dry weight, root fresh and dry weight, and leaf area increased significantly with raise of day temperature. stem height/stem diameter increased significantly at 30℃, but bolting was not observed. Leaf chlorophyll and nitrate content increased, whereas the vitamin C content of lettuce decreased with the increase of day temperature, and there were no significant effects on the soluble sugar. Taking the quantity and quality into consideration, the day temperature between 25℃and 30℃was the proper temperature for the production of lettuce.2. The effects of three different night temperatures(30℃/25℃, 30℃/20℃and 30℃/15℃)on the growth and quality of lettuce were investigated. The results showed that the shoot fresh and dry weight, root fresh and dry weight, and water content increased significantly with reducing of the night temperature from 25℃to 20℃, no effect significantly on the leaf number and leaf area, and the night temperature continue reducing, there were no significant effect on the growth of lettuce. The lower night temperature can restrain bolting. The vitamin C content and soluble protein of lettuce increased, whereas the soluble sugar and the nitrate decreased with the decrease of night temperature. Comparing to the effect of day temperature, there were less impact with different night temperatures, but remaining a lower night temperature was beneficial to the quality of lettuce.3. At two different day temperatures(20℃and 30℃), the effects of three different photoperiod(the time of illumination was 8h, 12h and 24h) on the growth and quality of lettuce were investigated. The results showed that the effect of photoperiod on the growth of lettuce was significant. The leaf number, shoot fresh and dry weight, root fresh and dry weight, and leaf area increased significantly with increasing of the time of illumination. At 20℃, the shoot dry weight and leaf area of lettuce on 24h illumination were as 13.3 and 7.0 times as these of lettuce on 8h illumination. There was no significant effect on the stem height/stem diameter with increasing of the time of illumination, and bolting was not observed. The soluble sugar of lettuce increased, whereas the soluble protein and the nitrate decreased with increasing of the time of illumination. The yield and quality of lettuce can be improved by increasing of the time of illumination.4. In this study, respectively the product of GDD and RDD and the product of thermal effectiveness and PAR as variables, a modified logistic dry matter production model was developed. Test data show that the dry matter production process of the greenhouse lettuce could be more accurately simulated with the product of thermal effectiveness and PAR as a variable to replace the time. The product of GDD and RDD and the product of thermal effectiveness and PAR both had a high correlation with LAI, and both of the two methods could accurately simulate the changes of the growth period of the lettuce's LAI. No matter what changes in the environment, there was a static relationship between the single lettuce leaf area and the parameters of the lettuce leaves patterns, and the single leaf area could be accurately estimated by these regression equations.
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