Interactive Effects Of Elevated CO₂ And Light Intensity On Photosynthetic Carbon Assimilation And Metabolomics Of Tomato

During winter and spring greenhouse tomato production,weak light and CO₂deficiency are the two major factors restricting its photosynthesis and yield.Both CO₂enrichment and light intensity enhancement are beneficial to improve tomato photosynthesis and yield,however,the mechanism of the interaction of CO₂ enrichment and light intensity affecting photosynthetic carbon assimilation is still unclear.In this study,Jinpeng No.1 tomato was used as test material,and different light intensities(200,300,400?mol?m^-2?s^-1)and different CO₂ concentrations(400 and 800?mol?mol^-1)were set to investigate the interactive effects of CO₂ enrichment and light intensity on tomato growth,photosynthesis,gene expression and metabolome.In addition,the correlation between photosynthetic parameters and other growth and physiological indexes was studied.Moreover,the effects of CO₂ enrichment and supplementary light on tomato photosynthesis and yield were studied.The main results are as follows:1.The interaction of CO₂ enrichment and light intensity significantly promoted light energy utilization and CO₂ fixation,and synergistically promoted tomato seedling growth and photosynthetic capacity.It significantly increased the specific leaf weight and seedling index.Both CO₂ enrichment and light intensity enhancement significantly increased net photosynthetic rate both at leaf surface and at chlorophyll level,and their interaction significantly increased leaf area level net photosynthetic rate,leaf apparent quantum efficiency and carboxylation efficiency.In addition,CO₂ enrichment significantly reduced stomatal conductance and transpiration rate,while the interaction significantly promoted net photosynthetic rate and plant dry matter accumulation,thus improving leaf water use efficiency both at level and at plant level.2.Effects of CO₂ enrichment and light intensity on stomatal morphology,leaf structure,biochemical substance content,enzyme activities related to carbon metabolism and gene expression were studied.Increased light intensity improved the stomatal length and width under CO₂ enrichment.Meanwhile,it promoted stomatal density,while CO₂enrichment reduced stomatal density,and their interaction significantly increased the thickness of leaves.CO₂ enrichment and increased light intensity significantly promoted the accumulation of soluble sugar in leaves by regulating the activity of sugar metabolizing enzymes,and the interaction had a significant effect on the soluble sugar contents.CO₂enrichment increased average enzyme activities of Rubisco,RCA,FBPase and TrxS by14.8%,19.4%,33.7%and 24.4%,respectively.Increased light intensity under CO₂enrichment significantly increased the above enzyme activities.CO₂ enrichment and light intensity interaction up-regulated the expression of genes related to carbon assimilation,thus affecting the enzymes'activity related to carbon assimilation,thus promoting photosynthesis and organic matter accumulation.3.The correlation between net photosynthetic rate and related indexes such as tomato plant morphogenesis,physiological and biochemical characteristics and gene expression level was studied.The plant morphological index,chlorophyll content,leaf nitrogen content,photosynthetic enzyme activity and expression level of key genes had significant linear correlation with leaf net photosynthetic rate.There was a significant linear correlation between seedling growth,water use and net photosynthetic rate.The results showed that CO₂ enrichment and increased light intensity were beneficial to improvement of plant morphological growth,chlorophyll content,activities of enzymes related to carbon assimilation and gene expression level,thus promoting photosynthetic carbon assimilation.Moreover,the improvement of carbon assimilation level in turn promoted seedling morphogenesis and plant water use efficiency.4.Metabonomics was used to study the differential metabolites and differential metabolic pathways related to photosynthetic carbon assimilation,which are affected by interaction of CO₂ enrichment and light intensity.CO₂ enrichment and their interaction increased the amount of differential metabolites in tomato leaves.The greater the difference in light intensity,the more the amount of differential metabolites,and the amount of up-regulated metabolites was found significantly higher than that of down-regulated metabolites.For the comparison of significant differential metabolic pathways between all treatments,CeLh vs CaLh had the most?63?,and CeLh vs CeLl was the second?60?,indicating that enhanced light intensity under CO₂ enrichment was beneficial to promoting changes in metabolic pathways,and vice versa.The most significant common metabolic pathways produced by increased light intensity under natural CO₂ were:ABC transporter pathway,metabolic pathway,galactose metabolic pathway,arginine and proline metabolism,starch and sucrose metabolism,while The most significant common metabolic pathways produced by enhanced light intensity under CO₂ enrichment were:ABC transporter pathway and amino acid biosynthesis pathway.The most significant common differential metabolic pathways produced by CO₂ enrichment were:amino acid biosynthesis,aminoacyl biosynthesis,ABC transporter and protein digestion and absorption metabolic pathways.CO₂ enrichment and increased light both significantly affected the following differential metabolic pathways related to carbon assimilation:galactose metabolic pathway?map00052?,starch and sucrose metabolic pathway?map00500?,and carbon metabolic pathway?map01200?.Furthermore,the significant differential carbohydrate metabolites induced by interaction of CO₂ enrichment and increased light intensity were:isomaltose,raffinose,UDP-D galactose,maltotriose,maltotetraose,sucrose,adenosine diphosphate ribose,acetylglucosamine and sucrose.5.Supplemental lighting significantly promoted tomato plant growth,net photosynthetic rate and fruit yield under CO₂ enrichment.Both CO₂ enrichment and light supplement significantly increased net photosynthetic rate of tomato,and the interaction between the two further promoted the photosynthetic rate and water use efficiency.In addition,CO₂ enrichment,light supplement and their interaction significantly increased the single fruit weight and yield per plant of tomato,and light supplement was beneficial to improve the nutritional quality of fruit.In autumn and winter tomato cultivation,CO₂enrichment(800?mmol?mol^-1)and supplementary light(200?20?mmol?m^-2?s^-1)is conducive to increasing tomato yield and fruit quality.To sum up,CO₂ enrichment and light intensity interaction promote photosynthetic carbon assimilation and growth by improving its leaf structure,leaf apparent quantum efficiency and carboxylation efficiency,up-regulating its carbon assimilation enzymes'activity and related gene expression,and promoting significant enrichment of carbon assimilation related differential metabolites and differential metabolic pathways.In addition,supplementing light under CO₂ enrichment was beneficial to increase plant photosynthesis and fruit yield of tomato.