| Vapor pressure deficit(VPD)is the main driving force of plant transpiration and the main factor of greenhouse environment regulation.Regulation of VPD has a significant impact on power and anatomy of water transport in plant.Nitrogen is the main element for crop growth and development.In view of the impact of climate drought,it is particularly important to explore the effect of regulating VPD on nitrogen absorption and photosynthetic physiological processes.In this paper,using tomato as material,through artificial climate chamber and greenhouse experiments,the effects of VPD and nitrogen coupling on nitrogen absorption and distribution,hydraulic characteristics,photosynthetic characteristics,leaf metabolites,etc.of tomato plants were studied and analyzed.The effects on the different metabolic pathways of leaves and fruit quality of plants were also studied,which provided a theoretical basis for the optimal regulation of VPD and nitrogen in the greenhouse environment.The main findings are as follows:(1)VPD and nitrogen supply levels had significant effects on plant nutrient uptake.Appropriate decreased VPD promoted the absorption of nitrogen,phosphorus,potassium,sulfur,boron,molybdenum and zinc elements.There was no significant effect on the content of calcium,iron and nickel in the whole plant,but the contents in different tissues were different.The increased surface area and volume of tomato roots and the activities of nitrogen assimilation-related enzymes were all beneficial to the absorption of nutrient elements.(2)The coupling of VPD and nitrogen affects the photosynthetic capacity of plants by changing the water conduction,CO2 conduction and photosystem activity of leaves.At the same nitrogen level,compared with the high VPD(HVPD)plants,the leaf thickness and spongy tissue thickness of the low VPD(LVPD)plants were significantly reduced,and the palisade/sponge tissue thickness ratio(P/S)were increased.Compared with the HVPD plants with the same nitrogen level,Kleaf increased by 4.00 % and 33.93% respectively(significant difference under the high nitrogen level),and the opposite was true in the low nitrogen level;the thickness of the sponge tissue decreased,the increase of palisade/sponge tissue and the up-regulation of aquaporin gene were all beneficial to increase leaf water conductance.Under normal and high nitrogen levels,the photosynthetic rate of LVPD-treated plants increased by 7.06% and 30.48%,respectively,compared with HVPD treatment,and the increase of chloroplast surface area(Sc/S)facing the intercellular space in leaves can increase the area of CO2 dissolution;the reduction of the distance from the chloroplasts to the cell membrane can promote the transmission of CO2;the light interception per unit area of the leaf and the amount of electrons transferred to the end of the electron chain are significantly increased,and the photosystem activity is higher,which is beneficial to improve the photosynthetic capacity of the plant.(3)VPD and nitrogen had effects on the metabolites and metabolic pathways of tomato leaves.The main metabolites that produce differences between treatments are nucleotides,amino acids,carbohydrates and vitamins,etc.The metabolic pathways where these metabolites are located mainly include galactose metabolic pathway,fructose and mannose metabolic pathway,starch and sucrose metabolic pathway,Glycolysis/gluconeogenesis,etc.Nitrogen reduction under HVPD treatment inhibited the accumulation of fructose,glucose and sucrose in tomato plants,and down-regulated the tonoplast sugar transporter gene(TST).(4)VPD and nitrogen affect the plant growth and fruit quality of tomato.Increased nitrogen application and high VPD can delay plant senescence,while LVPD can promote plant growth and development,resulting in early fruit ripening and improved fruit yield and quality.Under low,normal and high nitrogen levels,the yield of LVPD treated plants increased by 9.96%,10.19% and 7.83%,respectively,compared with HVPD plants. |
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