The Impact of Vessel Size on Vulnerability Curves: Data and Models for Within-Species Variability in Saplings of Aspen,Populus tremuloidesMichx

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Abstract
The objective of this study was to quantify the relationship between vulnerability to cavitation and vessel diameter within a species. We measured vulnerability curves (VCs: percentage loss hydraulic conductivity versus tension) in aspen stems and measured vessel‐size distributions. Measurements were done on seed‐grown, 4‐month‐old aspen (Populus tremuloides Michx) grown in a greenhouse. VCs of stem segments were measured using a centrifuge technique and by a staining technique that allowed a VC to be constructed based on vessel diameter size‐classes (D). Vessel‐based VCs were also fitted to Weibull cumulative distribution functions (CDF), which provided best‐fit values of Weibull CDF constants (c and b) and P50 = the tension causing 50% loss of hydraulic conductivity. We show that P50 = 6.166D−0.3134 (R2 = 0.995) and that b and 1/c are both linear functions of D with R2 > 0.95. The results are discussed in terms of models of VCs based on vessel D size‐classes and in terms of concepts such as the ‘pit area hypothesis’ and vessel pathway redundancy.