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.