Preliminary Study On The Physiological Characteristics,Quality And Disease Resistance Of Four Kinds Of LED Spectrum Combinations

As an important physical environmental factor,light plays a key role in plant growth and development,morphogenesis,photosynthesis and material metabolism.The new light source LED not only achieves the purity of monochromatic light,but also achieves a precise ratio of light color,which can form a spectrum similar to plant photosynthesis,The good energy-saving effect of LED has been fully applied in the fields of plant light supplementation and plant factories.In order to explore the effects of different combinations of spectra on the growth and quality of leaf lettuce,the experiment was based on red and blue combined light(RB,CK)under LED illumination and hydroponic conditions,respectively,adding purple light(RBP)and green light(RBG).Combined with yellow light(RBY),the composite light was studied to study the effects of different combined light sources on growth morphology,nutrient quality,photosynthetic characteristics,antioxidant capacity,nitrogen metabolism and disease resistance of leaf lettuce.The main findings are as follows:1.In the growth morphology of leaf lettuce,the combination of red,blue,green and red,blue and yellow can not only promote the growth of leaf lettuce and stem diameter,but also increase its fresh weight;The combination of red and blue light has a positive effect on increasing the dry weight of leaf lettuce;while the combination of red,blue and purple light inhibits the growth of leaf lettuce.2.The combination of red,blue and green combined light and red,blue and yellow light can increase the soluble sugar content of leaf lettuce;and the soluble protein and anthocyanin content of red,blue and purple combined light energy leaf lettuce;In terms of VC content,it was found that the combination of red,blue,purple,red,blue,green and red,blue and yellow can promote the VC content,wherein the red,blue and purple combined light VC content,followed by the red,blue and yellow combined light.3.In terms of nitrate content,the red,blue and green combination treatment had the lowest nitrate content,and the red and blue combination had the highest nitrate content.However,in the total nitrogen content,the red,blue and purple combination treatment and the red and blue combination treatment,the leaf lettuce leaves were all The nitrogen content is higher.4.The combination of red,blue,purple and red,blue and yellow light increased the total content of free amino acids in leaves of lettuce,followed by red and blue combined light;the total content of free amino acids in lettuce leaves under red,blue and green combined light was the lowest.5.Under the combined treatment of red,blue,green and red,blue and yellow,the content of chlorophyll and carotenoids in leaf lettuce leaves was higher,and the net photosynthetic rate of leaves was higher than other treatments;at 14 days after dimming,the red,blue and green combined light reduced the leaf stomatal opening,but increased the intercellular C02 concentration and transpiration rate,and further increased the net photosynthetic rate.6.At 14 days after dimming,the SOD activity was highest under the combination of red and blue combined light and red,blue and purple;the POD and CAT activities were the highest under red,blue and green combined light,while the SOD activity was lower;and the SOD was under red,blue and yellow combined light.The content of POD and CAT are both low.It can be seen that the addition of yellow light to the red-blue combined light has a certain inhibitory effect on the activity of oxidase.This effect is also reflected in the nitrogen metabolism enzymes.The activity of NR,NIR,GS and GOG AT is lower under the combination of red,blue and yellow light.On the contrary,the enzyme activities of red,blue,purple and red,blue and green combined light are higher.7.In the study of the resistance of leaf lettuce to gray mold and soft rot under different LED combination light,the preliminary results were obtained:leaf lettuce was inoculated with Botrytis cinerea under different combined light treatments,red,blue and purple.Leaf lettuce under blue-yellow combination light has higher defensive enzyme activity,followed by red,blue and green combined light.In vitro culture,red,blue,purple,red,blue and yellow combined light under the light of lettuce with gray mold and soft rot disease,followed by red,blue and green combined treatment,and red and blue combined light,whether gray mold or soft The incidence of rot is relatively high.It can be seen that the appropriate addition of violet or yellow light on the basis of the combination of red and blue light has a certain defense ability against the occurrence of lettuce gray mold and soft rot.In summary,the effect of composite light on the growth characteristics of leaf lettuce is complicated,and it is difficult to go to the next conclusion to explain which composite light is best.In order to improve the growth and quality of leaf lettuce,the appropriate addition of green light and yellow light on red and blue light can effectively increase the plant height,stem diameter,fresh weight and reduce the accumulation of nitrate content in leaf lettuce;Appropriate addition of violet light on the basis of blue light can effectively increase the content of soluble protein,anthocyanin and VC;in the photosynthetic characteristics,antioxidant and nitrogen metabolism enzyme activities of leaf lettuce,the best effect of adding green light on red and blue light is better;Regarding the resistance of leaf lettuce to gray mold and soft rot,it is preliminarily considered that it is appropriate to add purple light or yellow light under the combination of red and blue light.