Influence of nocturnal water dynamics on gas exchange and biomass accumulation in hydroponic basil

Plant growth is dependent on water status, which can be manipulated by altering the water potential in the root zone or modifying atmospheric humidity around shoots. Previous studies have demonstrated the possibility of enhancing biomass production by modifying leaf water status by applying less negative water potential around the rootzone, or by reducing nocturnal transpiration. However, whether a similar strategy benefits vegetative growth in leafy crops remains unclear. This study aims to investigate how the diurnal regulation of plant water relations influences the plant water status and biomass production of Thai basil. Thai basil was treated with low electrical conductivity (EC) of nutrient solution (EC 0.6 dS m −1 ), in order to increase leaf water status, during either the daytime or nighttime. Suppressing nocturnal transpiration by covering plants with a plastic at night was also applied as a method to increase leaf water status. Increased leaf water status did not stimulate biomass production; however, it significantly increased daytime gas exchange rates and led to a less negative leaf water potential during the next morning. Furthermore, suppression of nocturnal transpiration led to significant reductions in plant height and leaf area, highlighting the importance of nocturnal water flux in growth maintenance. Despite the observed growth reductions, inhibition of nocturnal transpiration promoted the accumulation of calcium in the foliage. Compared to Romaine lettuce, Thai basil exhibited a higher tolerance to osmotic stress. Overall, our findings indicated that increasing leaf water status did not necessarily translate to a change in biomass production in Thai basil.