The Effects Of Combine Vapour Pressure Difference And Soil Moisture On Growth And Development Of Tomato And Cucumber Plant

Vapor pressure difference（VPD）and soil moisture（SM）content is the two major environmental aspects that have an impact on plant physiological and developmental processes.The lower vapor concentration in air（which can be termed as high VPD or HVPD）under lower soil moisture content can negatively affect plant physiological and biochemical functions.It may lead to higher transpiration rate and might mimic drought stress in plants.In order to improve plants growth and development under lower soil moisture availability,and increase water use efficiency of plants,experiments were performed by decreasing vapor pressure（termed as low VPD or LVPD）under greenhouse conditions with cucumber and tomato as subject plants.The treatments included two levels of soil moistures i.e.,well-watered（WW）（90%）and water stress（WS）（60%）combined with two levels of VPD i.e.,low VPD and high VPD.High VPD was gained without controlling the air humidity during sunny hours which was approximately 3kPa to 6kPa in summer season,while 2.5kPa to 4.5kPa in winter.While,low VPD was maintained underneath 1.5kPa by means of a micro-fog system.In order to study the effect of VPD under lower soil moisture content,several plant morphological,physiological and biochemical activities were recorded in two test plants,i.e.tomato and cucumber in two seasons.Our results indicated that under lower soil moisture content,plants growth attributes and development was negatively regulated as compared to plants under well-watered.However,decreasing vapour pressure（LVPD）under limited soil moisture content revealed higher growth and improved physiology of plants.The plant height and stem diameter of tomato plants was increased by 0.7%and 10.7%,while 3.9%and 4.8%in case of cucumber under low VPD and WS（60%）conditions.The relative water content（RWC）of‘tomato’and‘cucumber’significantly increased by 12%and3%at flowering stage under low VPD and WS（60%）respectively.Lower soil moisture availability increase leaf electrolyte leakage from both cucumber and tomato plants,however,by decreasing vapour pressure（LVPD）,EC was increased by 8.8%and 6%at vegetative respectively.In both experiments during the early and last growth period,the effects of low VPD and low SM on the photosynthetic rate（Pn）of two cultivars were uneven.However,in tomato and cucumber at vegetative stage,the Pn was significantly increased by 9.2%and8.6%in low VPD and WS（60%）compared with high VPD and WS（60%）treatments.In both tomato and cucumber plants,intercellular CO₂ concentration was increased by 23%and50.7%,transpiration rate was increased by 24.8%and 21%and stomatal conductance by42.8%and 41%respectively.Furthermore,the higher antioxidant enzymatic activity such as superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）and ascorbic peroxidase（APX）and lower lipid peroxidation reveals efficient scavenging of reactive oxygen species,hence improving the plants ability to survive the shortage of water supplies.Overall,our study suggests that through inducing the combine impacts of VPD and SM can increase the functionality of hydraulic conductance and photosynthesis in vegetable production under controlled conditions in greenhouse.