Coordination Between Vapor Pressure Deficit?VPD? And CO₂ On Regulating Of Photosynthesis And Productivity In Greenhouse Tomato Production

Vapor pressure deficit?VPD?and CO₂ are the two important environmental factors that affect the growth of greenhouse crops,and they are also the main environmental factors that govern the cultivation of greenhouse tomato.The tests were conducted in summer and winter,respectively,and the test treatments were set as:CK treatment?high VPD with low CO₂concentration?,CO₂ treatment?high VPD with high CO₂ concentration?,VPD treatment?low VPD with low CO₂ concentration?and VPD+CO₂ treatment?low VPD with high CO₂concentration?.The highest VPD in summer greenhouse was over 6 kPa,the highest VPD in winter greenhouse was greater than 3 k Pa,and low VPD was set at approximately 1.5 kPa.The high CO₂ concentration was about 800±20?mol·mol^-1 and the low CO₂ concentration was about 400±20?mol·mol^-1.By investigating the effects of coordination of VPD and CO₂on tomato water status,photosynthesis,plant growth,water use efficiency and yield,the internal mechanisms of a series of changes were explored to provide a theoretical basis for tomato cultivation in the greenhouse.The experimental materials were drought resistant tomato cultivar‘Fenguan'and non-drought resistant cultivar‘Jinpeng'.The main research results obtained as follows:In the summer experiment:during the early and middle growth period,the effects of increased CO₂ on the photosynthetic rate?Pn?of two cultivars were inconsistent.However,in the late growth stage,the Pn was significantly increased compared with CK treatment.The Pn of‘Fenguan'increased 26.32%,and the‘Jinpeng'increased 57.64%,and the instantaneous water use efficiency?WUEi?of CO₂ treatment at the later growth stage were significantly increased by 61.10%and 63.73%of‘Fenguan'and‘Jinpeng'.Also,the final plant yield was both increased by 61.1%and 63.73%,respectively.The yield increased by 5.17%and 4.23%respectively.The VPD treatment significantly promote the Pn and WUEi in the early growth period of‘Jinpeng',there were no effect on Pn in the middle and later stage of both cultivar.Compared with CK treatment,the yield of‘Fenguan'and‘Jinpeng'increased by 11.12%and11.53%,respectively.The VPD+CO₂ treatment promoted the Pn of both two cultivars in every stage significantly,the Pn of‘Fenguan'increased by 26.74%,26.68%and 32.62%in turn,in the early,middle and late stages of plant growth.It increased by 79.27%,77.88%and78.41%of‘Jinpeng'.The water use efficiency?WUE?of‘Fenguan'and‘Jinpeng'significantly increased by 15.81%and 42.04%.The yield of two cultivar increased by 16.85%and 16.75%,respectively.One point must be noted is that VPD+CO₂ treatment reduces the number of flowers in the first spike of‘Jinpeng'.Therefore,in the summer facility cultivation,the effect of CO₂ treatment is significant in later stage of growth,the effect of VPD treatment is significant in early growth period.In addition,when the first ear blossoms,the treatment time of reducing VPD with enriching CO₂ in greenhouse must be reduced to ensure the opening of the first spike flower.Therefore,in the actual production,reducing the VPD and increasing CO₂ can further increase the photosynthetic rate of the plants,thereby increasing the yield.In the winter experiment:increasing CO₂ concentration could significantly increased leaf area,and the chlorophyll content decreased significantly in high VPD environment,while the chlorophyll content increased in the low VPD treatment.Compared with CK treatment,the Pn of‘Fenguan'increased by 32.15%,'Jinpeng'decreased by 19.34%,but there was no significant difference from CK treatment.The VPD treatment reduced the leaf area,25.35%of‘Fenguan'and 6.21%of‘Jinpeng',increased plant water consumption;and the Pn of‘Fenguan'increased 9.61%,‘Jinpeng'decreased 13.83%,but the differences were not significant.The total biomass of all the plants in VPD treatment decreased.The Pn of‘Fenguan'and‘Jinpeng'in VPD+CO₂ treatment increased by 8.81%and 23.50%,the WUEi increased by 432.2%and 469.1%of two cultivars.Plant biomass increased by 42.28%and38.32%of‘Fenguan'and‘jinpeng',respectively.Therefore,the plants grew best under VPD+CO₂ treatment environment in winter greenhouse.