Relationship between cavitation resistance and functional traits
Surprisingly, we observed no significant relationship between
P50 and functional traits (e.g. wood density, SLA, HV,
LDMC; Fig S4 supporting information) (Hacke et al., 2001; Markesteijn et
al., 2011; Schumann et al., 2019; Villagra et al., 2013). Of these
functional traits, wood density has received more attention in relation
to drought tolerance as greater structural investment (wood density)
would prevent xylem implosion, and thus greater resistance to embolism
(Hacke et al., 2001; Li et al., 2018; Markesteijn et al., 2011).
However, some other studies have also reported no significant
association between wood density and P50 (Larter et al.,
2017; Trueba et al., 2017). The non-significant relationships between
P50 and functional traits (e.g. WD and SLA) found by
Trueba et al. (2017) may be because species were pooled from diverse
communities and genera. Furthermore, there may be limited selective
pressure for investment in structural strength since our study sites
were well-watered, as studies have shown environment or site to be a
determinant of wood density (Downes et al., 2006; Onoda et al., 2010;
Roderick and Berry, 2002; Searson et al., 2004; Wimmer et al., 2002).
Leaf size traits were not important in pooling species apart in relation
to stem P50, as both broad-leaved and terete leaved
species are distributed within the arid and humid communities (Groom and
Lamont, 1996). However, in combination with Huber value, leaf size may
be important in highlighting species strategy to drought and across
climate/biomes. For instance in arid biome, species with reduced leaf
area to sapwood area employs avoidance strategy, while species with
greater surface area within the same system will tend to prioritize the
construction of xylem resistance to embolism (i.e higher stem
P50) for survival. Interestingly, we did not observe
significant relationships between hydraulic traits (HV and
P50). However, the direction of the relationship was
positive (R2 = 0.14, P value = 0.588) as expected
(Carter and White, 2009; Markesteijn et al., 2011). The weak
relationship suggests that not all species with higher
P50 (tolerance) necessarily had higher HV (avoidance)
(Fig S4, supporting information), as some species may either employ
alternate strategies for survival.