The links between leaf hydraulic vulnerability to drought and key aspects of leaf venation and xylem anatomy in a diverse group of Australian woody angiosperms.

Authors: BLACKMAN, CHRIS - Western Sydney University; Gleason, Sean; COOK, ALICIA - Macquarie University; CHANG, YVONNE - Macquarie University; LAWS, CLAIRE - Macquarie University; WESTOBY, MARK - Macquarie University

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2017
Publication Date: 3/18/2018
Citation: Blackman, C.J., Gleason, S.M., Cook, A.M., Chang, Y., Laws, C.A., Westoby, M. 2018. The links between leaf hydraulic vulnerability to drought and key aspects of leaf venation and xylem anatomy in a diverse group of Australian woody angiosperms.. New Phytologist. 10.1093/aob/mcy051.
DOI: https://doi.org/10.1093/aob/mcy051

Interpretive Summary: The ability of leaves to transport water under drought has recently been linked to several measurable properties of water-transporting “pipes” in vascular species (i.e., the vessels). However, the relative strength of these relationships across ecologically diverse groups of species has not been tested. We measured key aspects of vessel and leaf geometry among a group of 26 species, representing a wide range of drought tolerances, from four sites across coastal and inland eastern Australia. Among these species, variation in leaf vulnerability to drought was strongly related to the ratio of vessel wall thickness and the diameter of the vessel (“inside-pipe” diameter), hereafter denoted as (t/b)h, an index of vessel implosion resistance throughout the venation network of leaves. By “implosion resistance” we are referring to the negative pressure required to collapse a pipe, e.g., think of the way a milkshake straw collapses upon itself (thick milkshakes require straws with thick walls relative to their diameter). Our results suggest that vessel thickening, as expressed by (t/b)h, is a highly reliable indicator of leaf hydraulic vulnerability to drought, remaining closely linked to drought vulnerability across species irrespective of variation in leaf size.

Technical Abstract: The ability of leaves to maintain hydraulic function under drought has recently been linked to a number of different leaf venation and xylem anatomical traits. However, the relative strength of these relationships across an ecologically and morphologically diverse group of species remains untested. We measured key aspects of leaf venation, xylem anatomy and leaf morphology in a group of 26 species, representing a wide range of leaf drought tolerances, from four sites across coastal and inland eastern Australia. Across species, variation in leaf hydraulic vulnerability to drought (expressed as P50leaf) was strongly correlated with the ratio between vessel wall thickness and vessel lumen breadth ((t/b)h; an index of cell implosion resistance) within petioles, mid-ribs, 2nd order and minor veins, respectively. In contrast, variation in P50leaf was unrelated to the components of this ratio, th and bh, within low order veins, and was unrelated to both major vein density and leaf size. Our results suggest that xylem conduit reinforcement, as expressed by (t/b)h, is a highly reliable indicator of leaf hydraulic vulnerability to drought, remaining closely linked to P50leaf across species irrespective of variation in leaf size.