Investigating leaf trait coordination and its role in determining habitat suitability under current and future climate

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Anjum K. Gujral, Jason T. Cantley and Kevin A. Simonin, Department of Biology, San Francisco State University, San Francisco, CA, Adam B. Roddy, Department of Biological Sciences, Florida International University, Miami, FL

Background/Question/Methods: Leaf hydraulic conductance (Kleaf; the efficiency of water transport) constrains photosynthesis and plant growth as it directly influences the magnitude of stomatal conductance (gs) that can be supported while avoiding desiccation. The sensitivity of Kleaf and photosynthesis to water stress has long been investigated in terrestrial plants. However, to date, the leaf traits that control Kleaf and susceptibility to hydraulic dysfunction, as measured by water potential that induces 50% hydraulic failure (P50), are not well resolved. Most work in hydraulic efficiency and safety has been conducted on woody stems, and to a lesser extent, leaves of woody plants, with relatively little attention given to herbaceous species. Given the importance of plant water-use strategies to whole-plant carbon gain, a better understanding of coordination between Kleaf, P50, and leaf economic traits that influence relative growth rate is necessary. Through synthesizing previously published data on woody plants and gathering new data on herbaceous species, this study aims to elucidate leaf trait coordination between Kleaf per unit mass (Kleaf mass), leaf hydraulic vulnerability (P50leaf), minimum leaf water potential (ψmin), turgor loss point (ψTLP), leaf mass per area (LMA), leaf size (LA), and vein density (VD).
Results/Conclusions: This analysis investigates leaf trait coordination in approximately 200 species from 70 vascular plant families. Preliminary results support a negative relationship between LMA and Kleaf mass, suggesting a trade-off in carbon allocation between hydraulic efficiency and leaf longevity as Kleaf mass and drought tolerance interact to control the lifetime carbon gain of a leaf. Additionally, preliminary results indicate leaf size and hydraulic efficiency are decoupled, suggesting that plants with larger leaves are not better equipped for evaporative cooling than smaller leaves, which may place them at a greater risk of overheating in warm environments. A trade-off between hydraulic efficiency and vulnerability to hydraulic failure has been hypothesized; however, investigations have not found strong support for a strict efficiency versus safety trade-off. Given that Kleaf constrains operational stomatal conductance, decoupling between Kleaf and P50leaf would allow plants that inhabit low humidity environments to maintain photosynthesis during periods of low water availability, especially herbaceous plants with shallow roots. Physiological trade-offs in leaves may represent meaningful syndromes or strategies of whole-plant function and clarifying the relationships between these leaf traits allows for greater understanding of plant responses to a warmer, and in some cases drier, future climate.