| The aim of this study was to discuss the effects of the intermittent and continuous lightsupplement on the growth, morphology and physiology of lettuce. This experiment of lettucecultured under4different duty ratio of LED:25%,50%,75%and100%. The growth process,morphological change, production, quality and photosynthetic characteristics of lettuce wasmeasured. Evaluate the effects of intermittent and continuous light on growth of leafvegetable and luminous efficiency. This research have important implications and referencefor light utilization efficiency. The result as followed:1. The morphology, growth, biomass allocation and photosynthesis of lettuce culturedunder intermittent or continuous light is different. Duty ratio from two aspects of stage lightand dark influence the growth of lettuce, the interaction of both light and dark stage influencethe photosynthesis pathway, growth, development, morphogenesis and yield formation.2. Plant height, leaf number, leaf length, leaf width, leaf area increased with the treatingtime. Lower duty ratio is benefit to increased of plant spread, which is benefit to obtain morelight energy. The plant height of T1, T2, T3had increased by382.43%,82.43%,62.16%incontrol. The fresh stalk and leaf mass, dry stalk and leaf mass increased with the increase ofduty ratio, except for continuous treatment, but the difference among different treatmentswere not significant. The fresh stalk and leaf mass of T2, T3had increased by11.94%,24.96%in control. Root fresh mass, root dry mass increased with the increase of the dutyratio, the significant differences between the treatments. The root fresh mass of T1, T2, T3had decreased by40.51%,24.05%,16.46%in control. Root-shoot ratio increased with theincrease of the duty ratio, there was no significant difference between intermittent lighttreatment, the difference between intermittent and continuous light were significant differently.The duty ratio enhanced the above-ground growth, inhibited under-ground growth. The lowerduty ratio can reduced the root volume, increased the root surface area and root length that aidplants in water and nutrient acquisition. On the one hand, relieve the high light stress of lowduty ratio, on the other hand, benefit offer more water and moisture for the above-ground. The Vc content, nitrate content and soluble protein content of each treatment at harvest decreasedwith the duty ratio increase. Duty ratio more lower with a higher secondary metabolitesproduction.3. Chlorophyll a content, chlorophyll b content, carotenoid content and chlorophyll a/bdecreased with the increase of duty ratio. There was significant difference in these treatments.The chlorophyll a content of T1, T2, T3had increased by105.52%,37.93%,24.14%incontrol. The chlorophyll b content of T1, T2, T3had increased by83.33%,41.67%,25%incontrol. The carotenoid content of T1, T2, T3had increased by83.33%,33.33%,16.67%incontrol. The chlorophyll a/b content of T1, T2, T3had increased by108.57%,32.86%,7.14%in control. The diurnal curve of net photosynthetic rate showed significant difference, the netphotosynthetic rate was variation by the changeable time. Diurnal maximal value of stomatalconductance of each treatments was seen at the beginning of a day, then with great fluctuation.Diurnal curve of intercellular CO2concentration represent increased during the day. The dailyvariation of transpiration rate has similar trends with stomatal conductance. The fluorescenceparameters were negative correlation with the increase of the duty ratio. The low duty ratioenhance the opening degree, the electron transport rate of photosystem Ⅱ, whereas the heatdissipation increase, the efficiency for solar energy utilization and the assimilation ratedecrease, the yield production decrease.Considering,75%duty ratio would be the better choice for illuminating lettuce. |
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