Coordination between vapor pressure deficit and CO2 on the regulation of photosynthesis and productivity in greenhouse tomato production

The high vapor pressure deficit (VPD) in some arid and semi-arid climates creates undesirable conditions for the growth of tomato plants (Solanum lycopersicum L., cv. Jinpeng). The global CO2 concentration ([CO2]) has also risen in recent years to levels above 400 mu mol.mol(-1). However, the coordinated effect ofVPD and [CO2] on tomato plant growth remains unclear, especially at VPDs of 5-6 kPa or even higher that are extremely detrimental to plant growth. Here, we explore the interaction ofVPD and [CO2] on plant water status, stomatal characteristics, and gas exchange parameters in summer greenhouses in a semi-arid area. Plants were grown in four adjacent glass greenhouses with different environmental conditions: (i) high VPD low [CO2] representing natural/control conditions; (ii) high VPD +/- high [CO2] representing enriched CO2i; (iii) low VPD +/- low [CO2] representing reduced VPD; and (iv) low VPD + high [CO2] representing reduced VPD and enriched CO2. Reducing the VPD alleviated the water stress of the plant and increased the gas exchange area of the leaf, which was beneficial to the entry of CO2 into the leaf. At this time, the increase of [CO2] was more beneficial to promote the photosynthetic rate and then improve the water use efficiency and yield.