Interactions between leaf form and biome
Arid plants show adaptations with small, terete, leaves, as seen in the
distribution of Hakea species in the southwest Australian Mediterranean
biome (Groom and Lamont 1996). While our findings do not support this
overall pattern, we observed a significant interaction between leaf form
and biome for drought tolerance. Broad-leaved species in the arid biome
were significantly more drought tolerant compared to broad-leaved
species in the humid biome (Fig 2). Broad leaves increase the surface
area for carbon uptake (photosynthesis) and transpiration, however
within warmer and drier sites, this may potentially lead to serious
water loss or cavitation (Wright et al., 2017). Thus, broadleaved
species within the arid biome would be more dependent on resistant xylem
(higher P50) to prevent implosion. Our results also
showed support for this (though not significant), as broadleaved species
within the arid biome generally had higher P50 compared
to terete leaved species in the same biome (Fig 2). This finding
highlights the ability for different strategies to co-exist in the arid
biome, and the importance of understanding trait coordination alongside
climate drivers for drought adaptation.