Collaborative Research: Conifer leaf anatomy determines hydraulic functioning

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Conifers are globally important, both ecologically and economically. Many conifer species have recently experienced extreme mortality events due to drought, fire and insect outbreaks. There is an urgent need to understand conifer physiology, and especially conifer needles - the organs responsible for carbon uptake and regulation of water loss. Conifers have an intriguing paradox in the link between their leaf anatomy and physiology: with such a simplistic, single-vein vascular system, how can they compete with broadleaf species or inhabit extreme environments? This project aims to understand how conifer leaf anatomy influences water transport and photosynthesis, and how needle water transport declines during drought. This information will then be used to develop a mechanistic model to help predict forest productivity and mortality in response to drought and other environmental challenges. The project will provide training for a postdoctoral researcher, a graduate student, and multiple undergraduate students. Also, in collaboration with the McCall Outdoor Science School, 5th and 6th grade students, their parents and teachers will participate in a workshop called "What happens inside a leaf?" To illustrate how cellular-level modifications can influence landscape processes, 3D-printed conifer needle models generated from X-ray imaging will be used. Anatomical models will be freely available through a website for teachers and students to 3D print hand-held models at schools, or as teaching kits for schools without access to 3D printing technology. Conifers inhabit some of the driest and coldest habitats where trees are found. Many conifer species are threatened by heat waves and droughts that induce physiological stress that can make them more vulnerable to pests and pathogens. Although most conifer leaves have only a single vein supplying water to the leaf, the internal anatomy outside the vein is incredibly diverse across the conifer phylogeny. The impact of this diversity on water transport and carbon uptake is unknown. The primary goal of this project is to develop a mechanistic framework to understand the influence of conifer leaf anatomy on leaf hydraulic conductance and photosynthetic capacity. This mechanistic understanding will be used to illuminate how conifers have adapted to arid and cold environments and have also been able to successfully compete with angiosperm species over evolutionary history. The project will combine state-of the art 3-dimensional imaging methods (high-resolution X-ray computed micro-tomography) with a hydraulic model and measurement of leaf hydraulic conductance to clarify the impact of conifer leaf internal anatomy on hydraulic function.