Physiological Response Of Tomato Growth To Weak Light With Different Light Densities

Tomato is one of the most widely cultivated fruits and vegetables in the world,and is the main horticultural crop cultivated in greenhouse in southern and northern China.It has high yield,rich nutrition,good processing properties and high economic value.Due to the light-happy characteristic of tomato,the yield and quality of tomato are often reduced due to the lack of light density in greenhouse in winter and spring cropping in Yangtze River Delta and northern China.However,in the scenario of weak light stress in greenhouse tomato cultivation,how to accurately supplement light,how to determine the lowest and optimal optical density value to be reached by supplemental light,and what is the basis for determining the optical density of supplemental light?The results of existing studies do not provide a reasonable answer.In addition,as for the physiological response of tomato to low light,although previous researches have been conducted in different growth stages under low light stress in natural and semi-natural state,there has been no report on the study of low light stress under artificial light environment during the whole growth period.According to the conclusions of previous studies,the light intensity of 300μmol m^-2s^-1is a more appropriate light density for greenhouse tomato cultivation under full artificial light environment,and it is also a reasonable and widely used light density for supplementary light cultivation in greenhouse.In view of this,this study in order to"red dwarf"tomato varieties as experimental material,set different gradient in total artificial indoor light environment of weak light density processing experiment and study the different density of weak light on tomato morphology and physiological growth,photosynthetic physiology,glucose metabolism,biomass allocation,yield and quality,the influence of the power conversion efficiency.The main research results are as follows:（1）By setting weak light test of 300,250 and 200μmol m^-2s^-1with different gradient optical density,the growth period was prolonged as far as possible.Through the collection and analysis of test data,it was found that:The plant height/stem diameter,average node spacing,stem diameter after 49 days of light treatment,the number of nodes after 28 days of light treatment and the index of small fruit percentage of tomato plants in the whole growth period had significant differences among the three kinds of light density weak light treatment,while the other morphological indexes,flowering and fruit yield indexes had no significant differences.With the increase of optical density,the flowering time of tomato was advanced,and the yield,average single fruit weight and large fruit percentage were increased,but the differences were not significant.The results showed that 300,250 and200μmol m^-2s^-1light intensity treatments had significant effects on the morphology and small fruit percentage of tomato,but had no significant effects on flowering,fruit bearing and yield.（2）Based on the results of（1）,two different gradient optical densities of 80μmol m^-2s^-1and 150μmol m^-2s^-1were added.The effects of low light intensity of 300,250,200,150and 80μmol m^-2s^-1on tomato morphology and growth,photosynthetic physiology,glucose metabolism physiology,biomass allocation,yield and quality,and energy conversion efficiency were further investigated.Study found:in the above five kinds of different optical density under low light environment,when the optical density is less than 200μmol m^-2s^-1,tomato plants have higher plant height,stem diameter finer,plant height/stem diameter larger,more internode number,the average spacing is longer,shorter length,leaf number,total leaf area decreases,and the morphological indexes showed that the plants showed a trend of moderate growth;The SPAD value,photosynthetic pigment content,net photosynthetic rate,instantaneous carboxylation efficiency and light energy utilization rate of leaves were significantly decreased.The biomass accumulation of the whole plant and each organ was significantly decreased,and the biomass allocation was significantly skewed towards stem and leaf.The flowering and fruiting stages of the first panicle were significantly delayed,the number of flowers and fruiting stages were significantly decreased,and the node position was significantly increased.The number of flowering and bearing decreased,the fruit-setting rate decreased,the average fruit yield and average single fruit weight decreased significantly,and the small fruit rate increased significantly.The transverse diameter of fruit decreased significantly,and the fruit shape index increased significantly.The contents of soluble sugar,titratable acid,ratio of sugar to acid,soluble protein and vitamin C were significantly decreased,and the relative contents of flavonoids and anthocyanins were significantly decreased.The efficiency of electric energy conversion is significantly reduced.When the optical density was greater than or equal to 200μmol m^-2s^-1,there were significant differences in some morphological indexes of tomato,leaf pigment content,titratable acid,soluble sugar,sugar-acid ratio,vitamin C content,flavonoids and anthocyanins relative contents between 200,250 and 300μmol m^-2s^-1treatments.There was no significant difference in other indexes.The results showed that there were no significant differences in tomato morphology and growth,photosynthetic physiology,glucose metabolism physiology,biomass allocation,yield and quality,and energy conversion efficiency among different optical density treatments of 200,250 and300μmol m^-2s^-1.Can ensure the normal growth and fruit of tomato plants in the whole growth period;However,80 and 150μmol m^-2s^-1treatments showed poor performance and could not guarantee the normal growth and development of tomato plants during the whole growth period,and 80μmol m^-2s^-1treatments even could not guarantee the normal fruit of tomato plants.In conclusion,80μmol m^-2s^-1is the minimum optical density threshold to ensure tomato fruit,and 150μmol m^-2s^-1is the minimum optical density threshold to ensure the growth and development of tomato in the whole growth period.200～300μmol m^-2s^-1is a reasonable optical density threshold based on low energy consumption,which can meet the normal growth and development of tomato in the whole growth period.In practice,we only need to meet the requirement that the total light density of tomato canopy reaches 200μmol m^-2s^-1,so as to ensure the normal growth of tomato under the weak light stress of protected culture.Thus,the cost of filling light is further reduced and the planting benefit is improved.