Xylem vulnerability of vegetative vs reproductive organs
The xylem supplying water to reproductive tissues was more resistant to cavitation than that supplying vegetative tissues (fig. 4). Peduncles were typically the last tissues to cavitate by >50% in each individual (fig. 4). Within individuals the peduncle P50 was typically lowest relative to that of leaves, petals, and petioles (fig. S1). In contrast the petiole P50 was highest in 4/5 plants (fig. S1). This pattern between organs was supported by the results of ANOVA in that organ type had a significant overall effect on P50 (P=0.002**) (table 1). The mean P50 of peduncles (-2.13MPa ± 0.21) was found to be significantly more negative than that of petioles (-1.39MPa± 0.10) leaves (-1.53MPa± 0.13) and petals (-1.32MPa± 0.15) (fig 5.). No differences were observed between the P50 of vegetative tissues and petals, but peduncles were consistently more resistant to cavitation, with lower P50s than the other organs (fig. 5). The mean P50 for stems, however (-1.91MPa± 0.28, fig. 5) was similar to the P50 of the peduncles (P=0.55).
The mean P50 (-1.91 ± 0.28MPa) and P88 (-2.66 ± 0.31MPa) of stems was not significantly different (P>0.05 in both cases) to the P50 (-2.13MPa ± 0.21 MPa) and P88 (-2.24 ± 0.21) found in peduncles, showing substantial overlap in the cavitation resistance of these organs (fig. 4 and 5). The stem cavitation within individuals showed a pattern of cavitation that began comparatively early at hydrated water potentials, but continued cavitating until low water potentials in a similar way to peduncles (fig. S2).