Putting the puzzle together : investigating hydraulic functioning and water transport at high spatial resolution in tall trees

Understanding of tree water use ranging from individual to ecosystem scale has greatly progressed over past decades. However, studies that integrate measurements of tree water use, physiological functioning, wood anatomy and whole-tree architecture are scarce, and are needed for developing a holistic perspective on plant function and responses to environmental drivers. Here we introduce the experimental design of a research project (December 2012 - March 2013) to provide novel insights to whole-tree hydraulic function of tall trees (>20 m). The study focuses on Eucalyptus grandis, an evergreen angiosperm native to eastern Australia. The experiment used a large number of sap flow sensors distributed among 12 trees in a forest plantation at different levels of intensity - the most intensively studied tree had 52 sap flow sensors installed along its vertical axis and in all branches of the lower-, mid- and top-canopy. Parameters describing stem and branch architecture have been recorded. In addition, we operated a number of other sensor types at various heights within the trees (dendrometers, psychrometers, linPAR sensors, microclimate loggers) and belowground (soil temperature and moisture) to further complete information about the movement of water and key environmental variables. Leaf water potential, net photosynthesis and stomatal conductance were measured for three full diel cycles during early-, mid- and late-summer 2012-2013. At the termination of the experiment, trees were felled to facilitate assessment of branch traits (e.g., SLA, total branch leaf area). Wood was extracted from all locations of sap flow measurement to determine anatomical characteristics of vessels and to allow reconstruction of water conducting networks. Finally, all streams of information (hydraulic, physiological, anatomical, environmental) were merged to systematically reconstruct the tree in virtual space, developing a 3-dimensional representation of in situ water flow through vessel networks under varying natural environmental conditions.