Stomatal characteristics and desiccation response of leaves of cut chrysanthemum (Chrysanthemum morifolium) flowers grown at high air humidity

Although it is well known that, as a short-term response, stomata close at low relative humidity (RH) (high Vapour Pressure Deficit) and open at high RH (low Vapour Pressure Deficit), effects of long-term exposure to different Vapour Pressure Deficits (VPD’s) have only been studied in a few economically important horticultural crops, especially cut roses. To save energy costs, often low VPD conditions are present in greenhouses, due to low ventilation. We studied stomatal and desiccation responses of leaves of cut chrysanthemums after the plants had been exposed to different VPD conditions. While lower transpiration rate (E) was recorded for plants growing at low VPD (L-plants) in comparison with growth at moderate VPD (M-plants), higher stomatal conductance (g s ) was found in L-plants compared to M-plants. Bigger size of stomata and higher stomatal density were observed in L-plants. Besides differences in g s , E and stomatal characteristics during growth of the plants at different VPDs, stomatal closure response to desiccation (under the same VPD condition) was different when plants had been grown before at different VPD’s. Following desiccation, leaves of L-plants showed higher E compared with M-plants. Also E of leaves grown at moderate VPD but exposed to low VPD for only 5 days (M → L-plants) decreased less as response to desiccation than E of M-plants. After rapid desiccation, leaves of L and M → L plants had larger stomatal openings compared with leaves that were grown continuous at M condition, as indicated by their PSII efficiencies under non-photorespiratory conditions (Φ PSII ). In conclusion, control of VPD during growth will be important to prevent subsequent wilting of leaves of chrysanthemum cut flowers.