Leaf death during drought: quantification of lethal leaf water status and its anatomical and physiological correlates in Southern California native species

Background/Question/Methods

Leaf and whole plant responses to drought have long been studied, and are ever more critical to understand given ongoing climate change. However, we have lacked an approach to quantify lethal leaf dehydration, and the traits that plants may adapt to prevent this. To better understand the process of leaf death, we developed a new method to determine the lethal leaf water content, as that at which the leaf can only rehydrate to 50% of its original water content (LD50). We grew 25 species native to Southern California in a common garden experiment to enable the quantification of LD50, and additional drought tolerance traits especially those potentially contributing to the ability of the leaf to store and conserve water after stomatal closure, including leaf minimum epidermal conductance (g_min), turgor loss point (π_tlp), venation architecture, and leaf stomatal and cross-sectional anatomy. We hypothesized that (1) LD50 and associated drought tolerance traits would vary across species native to wet and dry habitats, and that (2) traits contributing to leaf survival of drought, including low LD50, g_min, and turgor loss point would be correlated across species. We also aimed to resolve traits that would better predict the ability of leaves to survive and recover after severe desiccation events.

Results/Conclusions

We found substantial variation (>4-fold) across species in LD50, and in g_min and other drought tolerance traits, supporting differences between wet and dry-habitat adapted species. We found novel relationships across species of traits related to leaf drought tolerance, including π_tlp, g_min, cuticle thickness, and stomatal traits. Using our dataset, we developed a novel approach to estimating the length of time that a leaf may survive during drought on stored water. We found this time to also vary strongly across species, contributing a new axis of variation important in defining a species’ drought tolerance. This study provides key insights into physiological limits of plant function, functional trait linkages and mechanistic drivers of leaf and plant drought tolerance and recovery.