Variation in stem P50 between species, biome,
and vegetation
There were significant differences in stem P50 betweenHakea species (P < 0.001, R2 = 0.98,
Table 2; Fig S5 supporting information). There was a continuous
variation in P50 across the 16 species sampled and
P50 varied 1.9-fold among species from -4.27 MPa
(minimum P50, H. archaeoides to -7.99 MPa
(maximum P50, H. grammatophylla ) (Fig 1).
Vegetation type was a significant factor in determining stem
P50 (P = 0.03, R2 = 0.45; Table 2),
such that species from the arid (-6.61 ± 0.42), mediterranean (-6.89 ±
0.23) and grassland vegetation (-7.15 ± 0.16) were more drought tolerant
than forest species (-5.17 ± 0.17). As predicted, there were significant
differences in stem P50 between biomes (P = 0.002, Table
2, Fig 1), such that species in arid biomes (-6.86± 0.18) were more
drought tolerant than species in humid biomes (-5.17 ± 0.17, Fig 1).
Biome differences explained 47% of the variation in stem
P50. The arid biome had greater variation among species
(-7.99 MPa H. grammatophylla to -5.07 ± 0.06 MPa H.
eyreana ; Table 3), compared to the humid biome (-6.65 MPa H .macraeana to -4.27 MPa H. archaeoides ; Table 3).