The leaf hydraulic conductance (Kleaf) is a critical bottleneck in whole-plant liquid transport, associated with the tremendous diversity across species in leaf structure (thickness, shape, venation architecture, stomatal pore area) and maximum rates of gas exchange. Additionally, Kleaf is dynamically linked with gas exchange for given species. In a series of systematic and mechanistic studies, the following specific hypotheses will be tested: (1) Kleaf imposes a consistent proportion of resistance in the plant hydraulic system, constraining maximum rates of gas exchange; (2) Kleaf is constrained by venation architecture; (3) Kleaf is dynamic, declining in low irradiance, and during leaf dehydration and ageing, due to xylem blockage and/or changes in membrane properties; these dynamics are importantly related to changes in gas exchange; (4) Kleaf is coordinated across species with structural traits associated with water flux through the leaf and gas exchange per area. This work will focus on both the mechanistic bases for these processes and the implications for whole plant function. Native Hawaiian species and invasive species will be studied in common gardens and across the dramatic natural moisture and soil age gradients of Hawai'i. Special focus will be given to the variation of of leaf hydraulic properties in the heteroblastic stages of native Acacia koa. The study will be expanded to include arboretum-grown species of Araceae with exceptionally diverse leaves. These studies will break new ground toward understanding of the integration of water transport and carbon assimilation at their nexus in the leaf. The work will provide detailed information of the extent, variation, mechanistic basis and dynamic nature of the role of leaf hydraulic conductance in the flow of water through plants, and in the evolution and function of diversity in leaf traits. The research will be integrated with undergraduate and graduate course teaching at University of Hawai'i, and with a new mentorship program to provide increased access for native Hawaiians to scientific training and careers, based on study of the unique, fascinating Hawaiian flora. In the Integrated Mentorship in Hawaiian Research, Education and Outreach, indigenous undergraduate students will be mentored part-time during semesters and full-time during summers in research, curriculum development, and outreach, grounded in Hawaiian plant biology. Mentored students will disseminate knowledge to the wider community by designing web curricula, giving educational tours, and by presenting annually in colleges and high schools, and at scientific meetings. The integrated research and education will contribute fundamentally to the understanding of leaf physiology, evolution and functional ecology; provide access for native Hawaiians to science; create resources on Hawaiian plant biology for scientists and educators; and increase global awareness and understanding of the unique Hawaiian biota.
