Stem sap flow (Q) and leaf turgor pressure (P c) were measured simultaneously on 4-year-old, 2.4m tall 'Arbequina' olive trees in a hedgerow orchard. Measurements were performed on well-watered control trees as well as on 60RDI and 30RDI trees (RDI=regulated deficit irrigation). The 60RDI trees received 59.2% of the crop water needs (ET c), and the 30RDI trees received 29.4% of ET c. P c was determined non-invasively using the magnetic leaf patch clamp pressure probe (ZIM probe). The patch pressure P p measured by the probe is inversely correlated with turgor pressure at P c>ca. 50kPa. P c is coupled with xylem pressure; thus P p yields information about the development of tension in xylem. In the case of the control trees a positive correlation between Q and P p was generally found, i.e. Q increased usually with increasing P p and decreased with decreasing P p, as expected. However, Q peaking did not always coincided with P p peaking at noon. Occasionally, Q peaking preceded or followed P p peaking with a time difference of up to 3h in both cases. Under some circumstances, the onset of Q after sunrise was greatly delayed, even though a pronounced increase of P p was observed. A delayed onset of Q after sunrise resulted in hysteresis phenomena, i.e. the linear increase of Q and P p in the morning hours did not coincide with the corresponding decrease of Q and P p in the afternoon. The development of severe water stress (P c

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