title: Stomatal closure of Pelargonium × hortorum in response to soil water deficit is associated with decreased leaf water potential only under rapid soil drying.
abstract: Soil water deficits applied at different rates and for different durations can decrease both stomatal conductance (gs ) and leaf water potential (Ψleaf ). Understanding the physiological mechanisms regulating these responses is important in sustainable irrigation scheduling. Glasshouse-grown, containerized Pelargonium × hortorum BullsEye plants were irrigated either daily at various fractions of plant evapotranspiration (100, 75 and 50% ET) for 20 days or irrigation was withheld for 4 days. Xylem sap was collected and gs and Ψleaf were measured on days 15 and 20, and on days 16-19 for the respective treatments. Xylem sap pH and NO3 (-) and Ca(2+) concentrations did not differ between irrigation treatments. Xylem abscisic acid (ABA) concentrations ([ABA]xyl ) increased within 24 h of irrigation being withheld whilst gs and Ψleaf decreased. Supplying irrigation at a fraction of daily ET produced a similar relationship between [ABA]xyl and gs , but did not change Ψleaf . Treatment differences occurred independently of whether Ψleaf was measured in whole leaves with a pressure chamber, or in the lamina with a thermocouple psychrometer. Plants that were irrigated daily showed lower [ABA]xyl than plants from which irrigation was withheld, even at comparable soil moisture content. This implies that regular re-watering attenuates ABA signaling due to maintenance of soil moisture in the upper soil levels. Crucially, detached leaves supplied with synthetic ABA showed a similar relationship between [ABA]xyl and gs as intact plants, suggesting that stomatal closure of P. hortorum in response to soil water deficit is primarily an ABA-induced response, independent of changes in Ψleaf .
authors.affiliation: The Lancaster Environment Centre, Lancaster University, Lancaster, Lancashire, LA1 4YQ, UK.
authors.forename: Richard K A
authors.initials: RK
authors.lastname: Boyle
authors.affiliation: The Lancaster Environment Centre, Lancaster University, Lancaster, Lancashire, LA1 4YQ, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: McAinsh
authors.affiliation: The Lancaster Environment Centre, Lancaster University, Lancaster, Lancashire, LA1 4YQ, UK.
authors.forename: Ian C
authors.initials: IC
authors.lastname: Dodd
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D057914:Agricultural Irrigation; D003890:Desiccation; D031316:Pelargonium / Q000502:physiology*; D010937:Plant Growth Regulators / Q000378:metabolism*; D018515:Plant Leaves / Q000502:physiology; D018517:Plant Roots / Q000502:physiology; D054046:Plant Stomata / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D012987:Soil / Q000737:chemistry; D013997:Time Factors; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000502:physiology
chemical_list: D010937:Plant Growth Regulators; D012987:Soil; D014867:Water; D000040:Abscisic Acid