Conservation, evolutionary and physiological ecology of plant drought tolerance: from ecotypes to ecosystems

Due to the projected increases climatic variability, including an increased frequency of extreme climatic events, such and droughts, flooding and fires, the mechanisms that plants use to access, transport and conserve water require critical and quantitative understanding. While there is a growing consensus that traits, such as the leaf osmotic potential at turgor loss point (πtlp), determine plants’ abilities to maintain photosynthetic performance and survive droughts, there has been little work to understand their inter-relationships, evolution, and how they scale up to overall plant performance and ecosystem functioning. During my PhD I focused on the integration of leaf and whole-plant traits to explain and predict plant vital rates and vegetation distributions with respect to climate. I showed that the stomatal conductance of Arabidopsis ecotypes and its relationship with climate is developmentally determined by the area of epidermal pavement cells and the stomatal initiation rate, and not the stomatal size. I determined that traits of California native oak species evolve in modules and that traits of Hawaiian native species from contrasting forests varied strongly and influenced species’ vital rates, with stronger relationships when stratifying by tree size. I also showed that species’ climate distributions across California can be predicted from traits and that traits and trait-trait intercorrelations change along a gradient of aridity in California. Ultimately, this work provided a new synthesis of the variation of trait-climate relationships across scales, opening new avenues for the inclusion of mechanistically informative traits to parameterize process-based models to test the ability to predict growth and mortality rates from trait networks, spatial neighborhoods, local topography, and climate across forests worldwide