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Majken Pagter, Karen K. Petersen, Fulai Liu, and Christian R. Jensen

Fuchsia (Fuchsia L.) is a popular woody ornamental, but it is very susceptible to frost injury during winter. As drought stress may be used to enhance freezing tolerance in woody plants, the effects of different types of water deficit on growth, selected physiological traits, and freezing tolerance were examined in Fuchsia magellanica Lam. ‘Riccartonii’. Drought responses were investigated after 6 weeks of pretreatment, where individual plants grown in a greenhouse under conditions of unrestricted water supply were compared with plants subjected to cyclic or continuous water deficit. After an additional 4 weeks of treatment at short day (10 h) and low temperature (8 °C day/4 °C night), freezing tolerance was examined. Both continuous and cyclic water deficit plants reduced water loss by reducing aboveground biomass and by efficient stomatal regulation. Continuous water deficit plants tended to adjust osmotically, while cyclic water deficit induced significantly higher xylem sap abscisic acid [(ABA)xylem] and leaf proline concentrations and a lower leaf water potential (ψl) than continuous water deficit, indicating that F. magellanica responds differently to continuous water deficit and to fast drying associated with stress phases of cyclic water deficit. The root water potential (ψr) and (ABA)xylem were negatively linearly correlated, implying that increasing water deficiency stimulated formation of ABA in the roots. An inverse, curvilinear relation between (ABA)xylem and stomatal conductance (g s) indicated that root-originated ABA might control g s during mild water deficits. Neither cold-acclimating conditions alone nor combined with water deficit increased stem freezing tolerance, indicating that F. magellanica lacks cold-acclimation ability under the inductive conditions used in this study.

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Nauja Lisa Jensen, Christian R. Jensen, Fulai Liu, and Karen K. Petersen

We investigated the effect of full irrigation (FI), deficit irrigation (DI), partial root zone drying (PRD), and nonirrigation (NI) on soil and plant–water relations, leaf stomatal conductance (g s), and abscisic acid (ABA) concentration in the xylem sap ([ABA]xylem) of pot-grown strawberry plants (Fragaria ×ananassa cv. Honeoye) in a greenhouse experiment. The DI and PRD treatments, irrigated with 70% of the volume of FI, reduced soil water content (θ), whereas crown water potential (ψcrown), leaf water potential (ψleaf), and g s were only significantly reduced from 11 to 15 days after initiation of irrigation treatments. Although [ABA]xylem was not significantly affected by the DI and PRD treatments, the NI plants increased [ABA]xylem, which coincided with decreased ψcrown, ψleaf, and g s 3 to 4 days after withholding irrigation. When ψcrown dropped below a critical value of −0.4 MPa, [ABA]xylem was linearly correlated with ψcrown. The g s tended to decrease as a function of [ABA]xylem, but g s was also affected by the water vapor pressure deficit (VPD) of the air. It is concluded that we did not observe a significant difference between strawberry plants grown in PRD and DI because ψcrown had to be below −0.4 MPa and soil water potential (ψsoil) had to be below −0.25 MPa before [ABA]xylem increased, these values were only reached toward the end of the experimental period (11–15 days after initiation of irrigation treatments).