Variation in species cavitation resistance across life history
traits
We observed significant species-specific variation in cavitation
resistance among Hakea species (Table 2), demonstrating that
species within the genus vary broadly in their capacity to tolerate high
levels of water stress. Differences in species drought tolerance (stem
P50) are largely attributed to the differences in the xylem structure;
e.g. pit membrane porosity and thickness, and conduit size (Choat et
al., 2012, 2008; Delzon et al., 2010; Li et al., 2016; Maherali et al.,
2004; Sperry et al., 2006). At maturity, xylem conduits are dead with no
possible acclimation to environmental change, making estimates of
drought tolerance via embolism resistance very important to make
reliable prediction under future climatic changes (Choat et al., 2012).
Species habitat preference and survival under disturbances (e.g. fire
and drought) within the Hakea genus have previously been reported
to be related with species life history and leaf form (Groom and Lamont,
1996). In contrast to our expectation, there were no significant
differences between resprouters and non-resprouters, as well as broad
and terete leaved species (Table 2). Previous studies have reported
contrary findings in relation to resprouting ability and drought
tolerance (Vilagrosa et al., 2014; Zeppel et al., 2015). The differences
between these studies and our study may be due to the fact that Zeppel
et al (2015) considered a large database of stem P50with species across different genus, indicating that resprouters were
more drought tolerant than non-resprouters, at least within Angiosperms.
On the other hand, Vilagrosa et al. (2014) used field observation and
stem hydraulic measurements focusing on 12 co-occurring woody species
within the Mediterranean system found that resprouters were less drought
tolerant than non-resprouters (i.e. seeders), in direct contrast to
Zeppel et al. (2015). In contrast to these studies, we focused on a
single genus across multiple biomes finding no difference in drought
tolerance with resprouting ability. This finding is partially supported
by Groom and Lamont (1996), who found resprouting ability amongHakea species within the Mediterranean biome of southwest
Australia was not associated with aridity. The differences may be due to
varying drought strategies (i.e. tolerators, avoiders) for survival
among genera and biomes.