Going with the flow: Structural determinants of vascular tissue transport efficiency and safety.
The woody tissue of flowering plants contains many vessels, which interconnect to form a vascular network responsible for the bulk transport of water through the plant. The structure of individual vessels, combined with network traits, such as the connections between vessels and the distribution of vessels of differing structural properties, determines the hydraulic efficiency and safety of the xylem tissue. In this issue, Mrad, Domec, Huang, Frederic, and Katul (2018) present a new model of xylem tissue function developed by combining information across multiple structural scales, including intervessel pit membrane and pore structure, vessel structure, and vessel network traits. This model was able to predict xylem hydraulic function in Acer and provides a new framework in which to evaluate the impact of vessel structural and network trait variation on hydraulic function and resistance to dehydration induced water transport failure (embolism). Declines in xylem conductivity during water deficit are often plotted as “vulnerability curves,” which depict hydraulic transport losses due to embolism formation in response to negative pressures in the xylem. The role of individual vessel structural traits, such as vessel diameter, on xylem tissue vulnerability to cavitation has been the focus of many studies, but few studies have combined traits across multiple scales (i.e., pits, vessels, and networks; Figure 1). In particular, understanding the role of network properties on hydraulic function has been rarely examined. The combination of modeling with plant anatomical and functional studies has potential to greatly advance understanding of these complex multiscale networks (Venturas et al., 2016). Mrad et al. discussed the implications of their results in the context of vessel connectivity and the scaling between pit and vessel structures. They identify the scaling between vessel and pit traits and how these determine the likelihood of embolism propagation