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Figure 1
Indirect measurement of cavitation in experiments using a collar pressure chamber in a walnut tree. The collar pressure chamber provides a way to generate external pressure on a portion of a branch. This external pressure, applied for 2 min. intervals in these experiments, is transmitted within the conducting system, and it can induce different degrees of cavitation. During the first day, a pressure of 1 to 2MPa was applied without any effect on the sap flow. On the second day, higher pressure were applied and no changes in sap flow were observed below pressures of 2.4 MPa. For pressures between 2.4 and 2.6 MPa, some cavitation was induced, as shown by the reduction of the sap flow, as compared with the control branches. Around 4 PM a pressure of 3 MPa was applied. For walnut, the vessels are completely cavited at this pressure and no more sap flow occurrs. No sap flow was observed through the pressured branch on the third day, indicated that the discountinuity of the water column caused by cavitation was permanent (Ameglio et al. 1994).
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