Effects Of CO₂ Enrichment On Growth And Physiological Characteristics Of Tomato Seedlings Under Water Stress

To explore the effects of CO₂ enrichment on the growth and physiological characteristics of tomatoes under water stress,and to provide theoretical basis and technical support for the improvement of CO₂ fertilization efficiency and tomato resistance under water stress in the future,this experiment took’Jinpeng No.1’tomato seedling as experimental material,adopted split zone design,the main factor was CO₂ concentration,atmospheric CO₂ concentration(400μmol·mol^-1)and enriched CO₂ concentration(800±40μmol·mol^-1),the splitting factor was soil water treatments,which were normal water treatment（RWC=80±5%）,waterlogging stress treatment（water completely submerged root system）and drought stress treatment（RWC=50±5%）respectively.The effects of CO₂ enrichment on growth,photosynthesis,carbon metabolism,antioxidant system,and endogenous hormones of tomato seedlings under waterlogging stress and drought stress were studied.The main research results are as follows:1.CO₂ enrichment alleviated the inhibitory effect of water stress on the growth of tomato seedlings:CO₂ enrichment increased the leaf area and dry weight of tomato seedlings under waterlogging stress,and increased the stem diameter,leaf area,dry fresh weight,and seedling index of tomato seedlings under drought stress;CO₂ enrichment increased the root activity under waterlogging and drought stress.CO₂ enrichment increased leaf relative water content and leaf thickness under waterlogging stress and drought stress.2.CO₂ enrichment increased intercellular CO₂ concentration,increased net photosynthetic rate,and decreased stomatal conductance and transpiration rate;CO₂ enrichment significantly increased the activities of Rubisco,RCA,PGAK,GAPDH,and Ru5PK under drought stress,but the effects of waterlogging stress on Rubisco,PGAK,GAPDH,and Ru5PK were not obvious.The effect of CO₂ enrichment on photosynthetic pigment content was not obvious.3.CO₂ enrichment increased the accumulation of non-structural carbohydrates in tomato seedlings under water stress:drought stress and waterlogging stress significantly increased the contents of fructose,reducing sugar,sucrose,and total sugar,but decreased the content of starch.CO₂ enrichment increased the contents of non-structural carbohydrates such as fructose,reducing sugar,sucrose,total sugar,and starch.At the same time,CO₂ enrichment also increased sucrose synthase activity,but the effect on sucrose phosphosynthase was not obvious.4.CO₂ enrichment alleviated the damage of reactive oxygen species in tomato seedlings under water stress.Drought stress and waterlogging stress increased the accumulation of reactive oxygen species,and also promoted the activities of superoxide dismutase（SOD）,peroxidase（POD）,and catalase（CAT）.CO₂ enrichment increased the activities of SOD,POD,and CAT in leaves and roots,decreased the accumulation of reactive oxygen species in leaves and roots under drought stress and waterlogging stress,and reduced the damage of reactive oxygen species.CO₂ enrichment promoted the further increase of proline and free amino acid contents under drought stress and improved the resistance of tomato seedlings,but the accumulation of osmotic regulatory substances under waterlogging stress was not obvious.5.The contents of growth-promoting hormone（IAA）,gibberellin（GA）,cytokinin（CTK）and ethylene（ETH）,and abscisic acid（ABA）in tomato seedlings under water stress were decreased under drought stress and waterlogging stress.CO₂ enrichment increased the contents of IAA,GA,CTK,and ETH,but decreased the content of ABA under drought stress and waterlogging stress.