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Fig. 2. Hysteresis in vulnerability curves. During dehydration, the percentage loss of hydraulic conductivity in xylem (PLC) increases because of cavitation. During rehydration, the dashed line shows the expected pattern where embolized xylem conduits are not refilled with water until the xylem pressure rises above the -2T/r limit (see text), which is very close to atmospheric. The left-hand limit is for a conduit filled with water vapor, and the right-hand limit is for an air-filled conduit. The dotted line shows a novel rehydration pattern reported for some species in which refilling occurs despite substantial negative pressures in the transpiration stream. From Hacke and Sperry (2003).
