UCLA

Plants experience a wide range of environmental stresses, and are expected to face more frequent and severe droughts under climate change. Understanding the impacts of stress on plant performance will allow us to predict changes in the distribution and abundance of plants across habitats. Despite this, few studies have analyzed plant drought tolerance within a lineage or species, rather than at a broad scale. I demonstrated the utility of the leaf osmotic potential at turgor loss point (πTLP; wilting point) for predicting drought tolerance across closely-related species of Ceanothus. I extended this work to examine how the osmotic potential at full turgor (πo), the main determinant of the πTLP, could be used to assess drought tolerance across individuals of a given species using model organism, Arabidopsis thaliana (Arabidopsis). I showed that the lack of a trade-off between growth and both drought tolerance traits and climatic drought in Arabidopsis could allow for the occupation of a large geographic and climatic range. I then combined an in-depth study of trait-trait and trait-climate relationships in Arabidopsis with an expansive study of genotypes spanning the species’ natural range to show that Arabidopsis can adapt to stress through both stress tolerance and avoidance, leading to unexpected trait relationships, and creating the potential to evolve under climate change. Adaptation to drought is influenced by many traits, including leaf venation architecture, which supplies water to the leaves allowing for photosynthesis to occur. I showed that major vein length per area (VLA) scaled with leaf size across ontogenetic stages, and provided evidence that while this scaling potentially leads to larger leaves having reduced hydraulic benefit relative to the increased construction and photosynthetic costs of leaf veins, they can offset this cost through vein tapering. Finally, I found that Arabidopsis vein mutants generally have reduced growth rates, opening the door to further research on the connection between vein traits and plant growth with applications to agricultural systems. Overall, this work demonstrates that in order to gain a deeper understanding of the complexities of plant drought tolerance we must examine it at multiple scales.