Effects Of Light Intensity Change On Growth And Photosynthetic Characteristics Of Tomato Seedlings

Artificial light source can realize the large-scale and efficient production of vegetables,but higher energy consumption of light source is the key factor restricting its development.Optimizing light parameters is essential to improve plant productivity and light utilization efficiency?LUE?.The photosynthate synthesized by photosynthesis,the activity of photosynthesis-related enzymes,and the stomatal conductance are known to show a single-peak curve with time under constant light intensity.Thus,the carbon fixation efficiency is continuously changing.There have been few reports on which period the light energy is more favorable for the accumulation of photosynthetic carbohydrates.Therefore,to explore the corresponding mechanism of plants light intensity at different time periods has great guiding significance to optimize light parameters and improve the utilization efficiency of artificial light source.Tomato?Solanum lycopersicum L.?,a main crop grown in protect horticulture,was chosen as the experimental material in this study.This plant was grown in substrate under the condition of artificial climatic chamber.The experiment was starting from seed germination.Treated as follow:different light intensities(50,100,200,400,600,800,and1000?mol?m^-2?s^-1),different light intensity distribution regime(CK:constant light intensity was 200?mol?m^-2?s^-1.The daily light integral of each treatment was the same,and 3distribution of light intensity regimes varied in a single peak curve.T1:the highest light intensity was concentrated at 12:30-15:30,T2:the highest light intensity was concentrated at11:00-14:00,T3:the highest light intensity was concentrated at 14:00-17:00.),and adjust light intensity distribution regime(CK:constant light intensity was 200?mol?m^-2?s^-1.The daily light integral of each treatment was the same.A1:light intensity was low in the middle of day,A2:light intensity was higher in the morning than afternoon period,A3:light intensity was low in the middle of day and higher in the morning than afternoon.The effects of light intensity changing on the plant growth and photosynthetic characteristics of tomato seedlings were analyzed from the following aspects:morphological establishment,biomass,light use efficiency,photosynthetic characteristics,stomatal characteristics,key enzymes for photosynthesis,gene expression,transcriptome and metabolomic analysis,etc.The main research results and conclusions were as follows:1.Effects of different light intensities on the growth of tomato seedlings.The increase in light intensity significantly promoted the growth and photosynthetic capacity of seedlings,but decreased the light use efficiency?LUE?.The increase in light intensity significantly promoted the increase in stem diameters,leaf number,leaf length,leaf width,and leaf area.LUE decreased with the increase in the light intensity.There was no significant difference in LUE when the light intensity was more than 400?mol?m^-2?s^-1.A constant light intensity less than 100?mol?m^-2?s^-1 or over 800?mol?m^-2?s^-1 would inhibit the normal growth of tomato seedlings.It was concluded that the light intensity of 200?mol?m^-2?s^-1 was most suitable for tomato seedling growth in the consideration of increased LUE and reduced energy cost.2.Light intensity variation treatment?T1,T2,T3?significantly inhibited the growth of tomato seedlings and reduced LUE.Light intensity variation treatment significantly reduced plant height,leaf number,leaf area,stomatal density,stomatal index,and other morphological indexes.This was not conducive to light energy capture and CO₂ absorption,thereby inhibiting the biomass accumulation?reduced by 17.4%?31.5%?.In addition,T1treatment significantly reduced the openness degree of PS?,down-regulated FDA activity and gene expression,and thus inhibited biomass accumulation.Compared with T1 and T3treatments,T2 treatment increased leaf area and promoted the capture of light energy;and reduced the stomatal and non-stomatal limit values,thereby improving the transpiration rate and Calvin cycle operating efficiency,which was beneficial to the biomass accumulation.3.Transcriptome analysis of tomato seedling leaves under different time periods of light intensity distribution.The number of genes with significant differences between T1treatment and CK was the highest,with a total of 1080,while the number of genes with significant differences between T2 treatment and CK was the lowest.Compared with CK treatment,there were 177 common differential genes in the 3 light intensity variation treatment groups.Light intensity variation treatment inhibited the expression of chlorophyll a oxygenase,phosphoenolpyruvate carboxylase,trehalose 6-phosphosynthase and aldose1-isomerase in the photosynthetic pathway,and finally reduced the accumulation of photosynthetic carbon product.4.Metabolomic analysis of tomato seedling leaves under different light intensity distribution periods.Compared with CK treatment,216 different metabolites were detected in the group of light intensity variation treatment,which were concentrated in amino acid metabolism,carbohydrate metabolism,and lipid metabolism pathways.T1 treatment promoted the photosynthetic carbon decomposition and transformation process,such as pentose phosphate pathway,citric acid pathway,photorespiration pathway,amino acid synthesis pathway,and promoted the synthesis of secondary metabolites.T3 treatment inhibited carbon metabolic pathways,such as attenuated pentose phosphate pathway,citric acid pathway and amino acid synthesis pathway,and reduced the metabolites.The variation difference between T2 treatment and CK was relatively low.From the above study,it could be concluded that the light intensity at different time periods had different effects on the physiology and biochemistry of plants.In addition,the pathways and the expression of related genes varied greatly at different time periods.5.Effects of light intensity readjust on growth and LUE of tomato seedlings.In A3group,the light energy was concentrated in the morning period which was favorable for carbon fixation,and the light intensity at noon?A3?was reduced as in that period,the photosynthetic carbon products would be consumed most.Compared with CK,A3 treatment increased the leaf area,leaf thickness,biomass and LUE of tomato seedlings.The total biomass of plants was increased by 15.7%and LUE was increased by 15%at 35 d after treatment.Under the artificial light environment,A3 treatment could improve the LUE and was more suitable for the growth of tomato seedlings.In summary,the light intensity concentration treatment affected the accumulation of photosynthetic products in different pathways and degrees,such as photosynthetic reduction power,photosynthetic carbon assimilation process,and carbon metabolic decomposition.In addition,concentrating the light intensity in the morning period,and avoiding the light intensity at noon was beneficial to improve the accumulation of photosynthetic products and LUE.