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The centrifuge method for measuring the resistance of xylem to cavitation by water stress was modified to also account for any additional cavitation that might occur from a freeze-thaw cycle. A strong correlation was found between cavitation by freezing and mean conduit diameter. On the one extreme, a tracheid-bearing conifer and diffuse-porous angiosperms with small-diameter vessels (mean diameter 40 μm) were nearly completely cavitated under the same conditions. Species with intermediate mean diameters (30-40 μm) showed partial cavitation by freezing. These results are consistent with a critical diameter of 44 μm at or above which cavitation would occur by a freeze-thaw cycle at -0.5 MPa. As expected, vulnerability to cavitation by freezing was correlated with the hydraulic conductivity per stem transverse area. The results confirm and extend previous reports that small-diameter conduits are relatively resistant to cavitation by freezing. It appears that the centrifuge method, modified to include freeze-thaw cycles, may be useful in separating the interactive effects of xylem pressure and freezing on cavitation.
Davis et al. (Fri,) studied this question.