Effects Of Frequency And Duty Ratio On The Growth And Photosynthesis Of Lettuce Using Light-emitting Diodes

In this study,the effects of the intermittent light of different frequencies and duty ratios with LEDs on the growth and photosynthetic characteristics of lettuce were detectived,in order to find the most suitable range of frequency and duty ratio,so as to achieve the purpose of saving energy and better quality and higher yield.This test used ‘Xianggang Boli' lettuce as test materials,and was conducted under the daily light integral of 5.62 mol·m-2·d-1.The control group was continuous LED light(CK)and the treatment groups were intermittent light with frequency,duty ratio and daily light-on hours of 1Hz/50%/24h(T1),1Hz/75%/16h(T2)and 10kHz/100%/24h(T3).The treatment days of lettuce were 28 days.Results were from three separate experiments.The morphological parameters,yield,quality and photosynthetic characteristics of lettuce during treatment and the power consumption of each treatment were measured.The main conclusions are as follows:1.The growth,quality and photosynthetic characteristics of lettuce had different responses to continuous and intermittent light,and there were significant differences in the power conversion efficiency of different treatments.The intermittent light treatments generally promoted the plant height stem diameter and leaf area of lettuce under the same daily light integral.The growth of lettuce was promoted by T2 and T3 at the whole plant level,by 59.02% and 60.68%,respectively.The fresh weight of stem and leaf of T2 and T3 was 59.02% and 60.68% higher than that of CK;and the root fresh weight was 54.18% and 67.19% higher than that of CK;and the dry weight of stem and leaf was 72.94% and 86.86% higher than that of CK,and the root dry weight was 76.30% and 68.74% higher than that of CK.2.Intermittent light treatment increased the Vc content of lettuce leaves,which was 8.78%,14.25% and 20.15% higher than CK respectively.The soluble protein content of T2 was increased by 11.18% compared with CK,and the difference of nitrate content between T2 and CK was not significant.3.Intermittent light reduced the contents of chlorophyll a,chlorophyll b,chlorophyll(a + b)and carotenoids in lettuce leaves except T3.Net photosynthetic rate of Intermittent light treatments was significantly lower than CK because of stomatal factors,and when duty ratio was high,lower emission frequency of light source could be used to alleviate the restrictions on photosynthesis which were caused by stomatal factors.The effect of frequency on lettuce photosynthesis is not significant in the case of high duty ratio.According to the chlorophyll fluorescence parameters,intermittent light did not decrease the original light energy conversion efficiency of photosynthetic system ? reaction center,but the heat dissipation increased,which led to reduced photochemical quenching coefficient,light system ? actual photochemical efficiency and relative photosynthetic electron transport rate.4.Intermittent light treatment improves the power conversion efficiency of the light source,the relative power consumption of each treatment was 1.44,1.26,1.31 and 1.48 KWh,respectively.The relative power consumption of T1 and T2 is 12.30% and 9.09% less than CK.The power conversion efficiency of T2 and T3 was significantly higher than CK,which was 92.50% and 82.50% higher than CK.5.Considering the yield,quality,photosynthetic characteristics and energy saving effect,the treatment T2 is more suitable for the actual production.