| Abstract: | To determine whether freezing causes wide-spread cavitationin the xylem of freezing trees, pressure and temperature weremeasured inside freezing conifer sapwood blocks. Pressure risesof up to 3.3 MPa were recorded and average radial growth velocitiesof ice were between 1.75 and 2.3 µm s–l. These growthvelocities of ice are less than the minimum growth velocityfor bubble nucleation during freezing. To complement this experimental study finite difference modelsof freezing in a single tracheid and freezing in an idealizedtree stem were constructed. The single tracheid model predictspressure rises similar to those measured experimentally. Thismodel also predicts that 5% to 8% of water in a tracheid lumenmigrates out of the tracheid during freezing. The tree stemmodel predicts growth velocities of ice three times faster thanthe values measured experimentally. These results are compared with previous contradictory theoriesof freezing in conifers. Key words: Freezing, xylem |
