Mechanisms Of Water Management On Plant Physiology,yield And Quality Of Tomato Under Doubling CO₂ Concentration

Water scarcity is a major challenge in the global agricultural development,and in recent decades,the problems with limited water resources have exacerbated due to greenhouse effect caused by increasing atmosphere CO₂ concentraction.In addition to water restrictions,the rising atmospheric CO₂ concentraction alters crop growth condition.Therefore,a better understanding of the underlying mechanisms of how reduced water supply affects the crop growth,yield and quality under doubling CO₂ concentration is crucial for developing irrigation strategies to enhance water use efficiency(WUE)without compromising yield and quality.Meanwhle,tomato,as a water-sensitive crop,has become an important model plant in plant physiological and biochemical studies.In this study,three pot-experiments in greenhouse were conducted on tomato plants with two CO₂ concentractions,including ambient CO₂(a[CO₂],400 ppm)and doubling CO₂(d[CO₂],800 ppm).In experiment I,two N levels,i.e.,N1,0.24 g kg^-1 and N2,0.48 g kg^-1 were used and the tomato plants were well-watered in the first three weeks after transplanting.Thereafter,the plants were subjected to progressive soil drying by withholding irrigation form the pots.In experiment II,tomato plants were subjected to three irrigation levels since anthesis:I1(irrigated to 90-95%pot water holding capacity,WHC),I2(irrigated to 70-75%WHC)and I3(irrigated to 50-55%WHC).In experiment III,tomato plants were subjected to three irrigation regimes from anthesis to fruit ripping:Full irrigation(FI,the whole pot was irrigated to 100%WHC),deficit irrigation(DI,whole pot was irrigated with 70%water volume used for FI),and alternate PRD irrigation(PRD,where 70%water volume used for FI was applied to one of the root compartments and the irrigation was alternately shifted between the two compartments,when the drying side had a decrease of soil water content ca.7-10%).In this work,the effects of nitrogen(N)supply on the response of leaf gas exchange,leaf water relations and plant nutrient uptake of tomato plants exposed to progressive soil drying under d[CO₂]were detected.Moreover,the response and mechanism of physiology,growth,yield and fruit quality to deficit irrigation(DI)and partial root drying(PRD)irrigation under d[CO₂]of tomato plants in two genotypes with contrasting endogenous ABA levels were investigated.The overall aim of the Phd project was to develop an effective strategy and scientific guidance for tomato production with limited water use under climate change scenarios.The main results of this study are as follows:(1)Effects of nitrogen(N)supply on leaf gas exchange,plant water relations and nutrient response to progressive soil drying in tomato plants under d[CO₂]were studied.During progressive soil drying,the leaf ABA concentration was increased with the decrease of the fraction of transpirable soil water(FTSW),which could induce the stomatal closure.d[CO₂]delayed the decrease of stomatal conductance and transpiration rate(not significant)during progressive soil drying.While,high nitrogen supply sensitized the stomatal response to drought,which was conducive to the plant to maintain the plant water status and cope with drought under drought stress.Moreover,both d[CO₂]and high N supply could improve plant WUE,and high N supply had the potential to alleviate the negative effect of d[CO₂]on plant nutrient acquisition.(2)The effects of deficit irrigation on the vegetative growth,nutrient uptake and WUE under d[CO₂]were explored.d[CO₂]increased leaf area,WUE and dry matter accumulation of tomato plants.However,DI reduced plant dry matter accumulation and water consumption of tomato plants.d[CO₂]enhanced the C content in stem,fruit and shoot,as well as S content in each part of the plant,while reduced the K content in stem,fruit and shoot,Mg content in shoot and N content in each part of the plant.Whereas,DI only significantly improved the leaf C content and shoot Mg content.In addition,d[CO₂]enhanced the Mg uptake in leaf,fruit and shoot.However,DI significantly reduced the N and C uptake in shoot.Furthermore,[CO₂]combined with DI obviously affected the plant C content,the leaf S content,shoot N and K uptake.(3)The effects of[CO₂],irrigation regimes and their interaction on fruit yield and fruit quality of tomato were investigated.The results showed that d[CO₂]enhanced the number of fruit and decreased the percentage of small fruit,resulting in higher fruit yield as compared to a[CO₂].Both reduced irrigation and d[CO₂]increased total soluble solid,vitamin C(Vc)and lycopene contents,while decreased nitrate content in fruit.The results indicated that there was a significant improvement in fruit quality of tomato plants with 70-75%WHC treatment at d[CO₂]environment.(4)The effects of PRD under d[CO₂]on vegetative growth,leaf gas exchange,dry matter accumulation,plant water relations and WUE of two genotypes of tomato were studied.d[CO₂]enhanced plant height,photosynthethisis rate,and lowered stomatal conductance and transpiration rate,thus increasing leaf WUE.Compared with a[CO₂],d[CO₂]increased the leaf water potential,osmotic potential and turgor pressure of tomato leaves.On the contrary,PRD significantly reduced leaf water potential,osmotic potential and turgor pressure of tomato leaves.In addition,[CO₂]and PRD also played an important role in changing the C and N content and uptake in tomato plants,and ionic concentractions in xylem sap.(5)Combined effect of PRD and d[CO₂]on the yield and fruit quality of two genotypes of tomato plants with contrasting endogenous ABA levels were studied.Tomato yield was more sensitive to irrigation regimes than[CO₂],and the reduction of fruit yield caused by PRD was attenuated under d[CO₂],especially in flacca.PRD enhanced the concentration of total soluble solid,total sugar and total acid,as well as fruit firmness.Meanwhile,the negative effect of d[CO₂]on fruit mineral nutrition was attenuated by PRD.Moreover,the effects of reduced irrigation regimes and d[CO₂]on plant physiology and fruit quality attributes are genotypic-dependent,where the endogenous ABA level of the plants plays an important role,and this must be considered in climate management in greenhouse tomato cultivation.