Figure 4. The impact of pre-existing embolized xylem area (%)
on the percent decrease in apparent P 50 of
un-embolized xylem in angiosperms (black) and conifers (white). The
conifer dataset includes a mean (n = 3, ± SE) for T. californica .
Rehydration of a L. benzoin leaf halted the spread of embolism
formation when only 20% of the xylem was embolized (Figure 5A). This
small percentage of embolism was concentrated in the midrib and major
veins (Figure 5B). In this leaf no embolism was observed on the second
dehydration until Ψ had declined to the value it was when rehydration
occurred. In a leaf of the same species in which 35% of the xylem area
was embolized, rehydration was only able to reduce the rate of embolism
accumulation (Figure 5C). In this leaf 9% of the xylem experienced
embolism after rehydration and before Ψ had declined to the value it was
when rehydration occurred; after reaching this Ψ the rate of embolism
formation increased (Figure 5C). Leaves of L. benzoin could not
be rehydrated once more than 50% of the xylem area embolized.