Effects of blue light on photosynthesis of Tradescantia virginiana plants grown in different VPDs

Quality of light received by leaves influences their photosynthesis. In current study, short-term effects of blue light were investigated in Tradescantia virginiana plants that have been grown in low and high vapour pressure deficits (VPD). Exposure to blue light decreased net photosynthesis (Pn) and internal carbon dioxide (Ci) compared to the control condition (combination of red (90%) and blue (10%) lights). During exposure to blue light, Ci values of high VPD-grown plants were higher than Ci values in the plants that were grown in low VPD. While, higher stomatal conductance (gs) and transpiration rate (E) were observed in low VPD-grown plants in comparison with gs and E values in high VPD-grown plants. After 30 minutes exposure to blue light, gs and E values were increased in both VPD conditions. Instant water use efficiency was decreased due to exposure to low VPD and blue light. There were no significant differences for PSII efficiency, non-photochemical quenching (NPQ) and leaf temperature between different VPDs, while exposure to blue light caused an increase in the NPQ. In conclusion, the results obtained from current study clearly showed that although blue light improved gs, it has negative effect on Pn. Furthermore, high VPD can optimize gas exchange and water conservation without negative effect on Pn in plant.