Figure 2

Sap collection methodology. Diagrams at top indicate the experimental sequence of (1) leaf removal to allow measurement of Ψ_leaf in a Scholander pressure chamber (applied pressure is equal, but opposite in sign, to Ψ_leaf), followed by (2) application of an overpressure to collect xylem sap from the detached leaf, (3) sealing the plant into the whole plant pressure chamber to collect xylem sap from the petiole stub by pressurising the root system, (4) removal of the whole shoot while the root system is under pressure to allow (5) xylem sap collection from the root system. Red bars in 1 and 4 indicate sites of organ excision. Applied pressure (a), sap flow rate (b) and xylem ABA concentration (c) of sequential samples collected from a typical AC plant. Each point is a separate measurement. Vertical dotted lines discriminate the three sources of xylem sap collected. Horizontal arrows in (b) indicate average whole plant transpiration rate over the 3 hours prior to leaf excision, and estimated leaf transpiration rate (assuming proportionality between transpiration rate and leaf area). Vertical arrows in (b) and (c) indicate mean (± SE) values of sap flow rate and xylem ABA concentration for the samples enclosed by a box, where SE is smaller than the symbol.