Vulnerability of vegetative and reproductive organs to xylem cavitation
Cavitation resistance varied significantly between organs of the same plant (P=0.002) (table S1). The xylem supplying water to reproductive tissues was more resistant to cavitation than that supplying leaves (fig. 4). Within individuals, peduncles were typically the most resistant organ (fig. 4). In comparison, petioles were the most vulnerable in 4 out of 5 replicates (fig. S2). Thus, the mean P50 of peduncles (-2.13MPa ±0.48SD) was significantly more negative than that of petioles (-1.39MPa±0.23SD), lamina (-1.53MPa± 0.28SD) and petals (-1.32MPa±0.32SD) (fig 5.). No differences were observed between the P50 of leaves (lamina and petiole) and petals.
The vulnerability curves of stem and peduncle showed significant similarities. Stem and peduncle P12 (-0.85MPa ± 0.56SD versus -1.53 MPa ± 0.54SD), P50 (-1.91MPa ± 0.57 SD versus -2.13MPa ± 0.48SD) and P88 (-2.66 MPa ± 0.57SD versus -2.24MPa ± 0.47SD) were not significantly different (P>0.05 in all cases), showing substantial overlap in the cavitation resistance of these organs (fig. 4 and 5). Cavitation events in the stem began at comparatively hydrated water potentials but continued until low water potentials in a similar way to peduncles (fig. S3).