Effect Of Light Intensity And Photoperiod On The Growth And Quality Of Hydroponic Lettuce

Artificial light plant factory has the advantages of high production,pollution-free and controllable,but it has the disadvantages of high cost and energy consumption.Light intensity and photoperiod are the main factors affecting plant energy consumption and the important light environment factors affecting crop growth.It is of great significance to promote and popularize plant factories to improve the efficiency of light use and regulate artificial light.In order to investigate the influence mechanism and growth law of artificial light quantity factor?light intensity and photoperiod?on the photosynthetic capacity of vegetables,ultimately,screen the suitable light formulas.In this study,Hong Kong glass fragile lettuce was used as test material?Yamasaki nutrient solution as hydroponic culture solution?.The effects of light intensity and photoperiod on photosynthetic characteristics,light energy utilization rate of hydroponic vegetables,and the regulation effects of enzyme activity were demonstrated by a combination of complete and fixed daily accumulation photon?DLI?experiments.In addition,the response of quality and yield to the photoperiod and light intensity;the combination of light intensity and photoperiod with high yield,high-yield,high-quality and energy-saving light intensity and photoperiod combination have been obtained,and light control modes have been proposed.The important research contents and conclusions are as follows.?1?The combination experiment of light intensity and photoperiod showed that the content of chlorophyll?Chl a+b?decreased,and the increase of carotenoid?Caro?content with increased the light intensity,Besides,incressing light intensity in favor of increasing net photosynthetic rate?P_n?and mesophyll conductance?g_m?,and heat dissipation increased?NPQ increased?.But F_v/F_m increased first and then decreased.Under the same DLI condition,increasing light intensity?shortening photoperiod?,Pn and F_v/F_m decreased.Cells were protected from photooxidative damage by increasing heat dissipation?NPQ?and enzymatic activity?SOD,POD,CAT?.Overall,Rfd-Lss values were higher at 150 and 200umol.m^-2.s^-1 light intensity,which was beneficial to electron transport and photosynthetic accumulation.Increasing DLI was beneficial to photosynthesis and could increase chlorophyll content,NPQ,photochemical quenching?qP?and antioxidant enzyme activity.The photosynthesis rate was affect by non-stomatal factor.The photosynthesis ability,leaf activity and resistance to oxidation in the early growth stage are better than those in the later stage.?2?The combination of light intensity and photoperiod experiment showed that increasing light intensity and extending light could promote the growth of lettuce leaves within the first 30 days after transplanting.16h/d photoperiod and 300?mol.m^-2.s^-1 light intensity was the optimal value of growth,16h/d,279?mol.m-².s^-1 is most conducive to growth within 30-40 days.Under fixed-day accumulation light quantum?DLI?combination experiment,leaf fresh weight,leaf area and root fresh weight of lettuce increased first and then decreased with the increase of light intensity?shortening of photoperiod?under the same DLI condition At the 20th and 40th days,and were higher at 150 and 200 umol.m^-2.s^-1light intensity.?3?As the increase of light intensity,soluble sugar,soluble protein and carotenoid content increased,but nitrate and VC content decreased,then presented a increasing trend,The longer photoperiod contributed to synthesize soluble sugar,soluble protein,VC and carotenoids,but depress nitrate,moreover,the principal component analysis showed that 300?mol.m^-2.s^-1 and 16h/d are most beneficial to lettuce quality.Under the same DLI conditions,soluble sugar content,VC content and carotenoid content increased first and then decreased with the increase of light intensity?photoperiod shortening?.Principal component analysis showed that low light intensity?long photoperiod?was beneficial to increase the soluble sugar,VC and carotenoid content of lettuce,but not conducive to reducing nitrate content and increasing soluble protein content.Under the same DLI conditions,the light intensity and photoperiod combination of the best quality was 150 umol.m^-2.s^-1 and 16 h/d.?4?During the whole growth period,both strong light and long light could improve the utilization efficiency of N and P elements,but it was detrimental to the utilization of K.The utilization efficiency of N and P was the highest in the first 10 days,and that of K was the highest in the last 10 days.Longer photoperiod can improve the quantum utilization efficiency of light.Under the same DLI condition,the quantum utilization efficiency of light increases first and then decreases with the increase of light intensity,and reaches its maximum at 150 umol.m^-2.s^-1 light intensity.