Genotypic Responses to Combined Effects of VPD and Salinity in Hydroponically Grown Tomato and Cucumber.

To reduce pressure on arable land and water resources, crops can be grown in controlled environments that allow one to recuperate water transpired by plants. This would reduce water demand and potentially allow the use of saline water. However, condensing atmospheric water affects the vapor pressure deficit (VPD), which will affect plant transpiration, nutrient transport, salt uptake, and ultimate growth. This study examined responses of two genotypes of tomato and cucumber during the vegetative phase to varying VPD levels (3.1 and 1.9 kPa) and NaCl concentrations (0 and 30 mM) grown in hydroponic solutions. Under higher VPD (3.1 kPa), transpiration significantly increased in both tomato and cucumber, driving higher water loss. In tomatoes, higher VPD (3.1 kPa) increased the total dry biomass of the Saluoso genotype from 4.3 to 7.1 g and of the Sweeterno genotype from 4.9 to 7.3 g. Root zone salinity diminished the differences in biomass induced by VPD, with little effect on biomass accumulation in both tomato genotypes. Root zone salinity consistently reduced dry weight in cucumber, lowering Addison's from 15.5 to 9.5 g and Proloog's from 13.5 to 10.0 g, regardless of VPD. Unlike tomato, cucumber did not respond to VPD and was more sensitive to salinity. These findings indicate that in hydroponic cultivation, particularly in protected environments, the possibility of producing clean water alongside crop production depends on species-specific responses. In tomatoes, high VPD enhanced growth and demonstrated compatibility with the use of saline water, supporting the dual goal of productivity and water recovery. However, in cucumbers, the sensitivity to salinity and lack of response to VPD highlight the need for careful species selection and management to achieve sustainable water use and crop production.