Cavitation in plants at low temperature: is sap transport limited by the tensile strength of water as expected from Briggs' Z-tube experiment?

ABSTRACT

Xylem cavitation in plants is thought to be caused by a loss of adhesion at the conduit wall surface because a rupture in the body of the water column was implicitly ruled out by an experiment by Lyman J. Briggs with Z-tube capillaries. However, Briggs reported a drastic increase in cavitation pressure of water below 5 degrees C which, if it were also true in xylem conduits, would suggest that water transport in plants could be limited by water cohesion at low temperature. In this study we have repeated Briggs' experiment using stem segments. Xylem vulnerability curves were obtained with a centrifuge technique at 1, 25 and 50 degrees C on yew (Taxus baccata). Contrary to Briggs' finding, vulnerability to cavitation, measured as per cent loss conductance, did not increase sharply at 1 degrees C and was even less than at 25 degrees C and 50 degrees C. Moreover, the onset of cavitation in yew at 1 degrees C was measured at a much more negative pressure than Briggs' value. This points out an artefact in Brigg's experiment at low temperature possibly related to imperfections in the tube walls which act as cavitation nuclei.