Sebastian Pfautsch1*, Michael J. Aspinwall1,2, John E. Drake1,3, Larissa Chacon-Doria4, Rob J. A. Langelaan4, David T. Tissue1, Mark G. Tjoelker1 and Frederic Lens4
1. Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, 2751 NSW, Australia,
2. Department of Biology, University of North Florida, Jacksonville, FL 32224, USA,
3. College of Environmental Science and Forestry, State University of New York, Syracuse, NY 13210, USA, and
4. Naturalis Biodiversity Center, Leiden University, P.O. Box 9517, 2300RA Leiden, The Netherlands
*For correspondence. E-mail [email protected]
(Received: 12 May 2017 Returned for revision: 2 August 2017 Editorial decision: 23 August 2017 Accepted: 6 October 2017)
Background and Aims
Sapwood traits like vessel diameter and inter vessel pit characteristics play key roles in maintaining the hydraulic integrity of trees.
Surprisingly little is known about how sapwood traits covary with tree height and how such trait-based variation could affect the efficiency of water transport in tall trees.
This study presents a detailed analysis of structural and functional traits along the vertical axes of tall Eucalyptus grandis trees.
To assess a wide range of anatomical and physiological traits, light and electron microscopy was used, as well as field measurements of tree architecture, water use, stem water potential, and leaf area distribution.
Strong apical dominance of water transport resulted in increased volumetric water supply per unit leaf area with tree height.
This was realized by continued narrowing (from 250 to 20 μm) and an exponential increase in frequency (from 600 to 13 000 cm−2) of vessels towards the apex.
The widest vessels were detected at least 4 m above the stem base, where they were associated with the thickest inter vessel pit membranes.
In addition, this study established the lower limit of pit membrane thickness in tall E. Grandis at ~375 nm.
This minimum thickness was maintained over a large distance in the upper stem, where vessel diameters continued to narrow.
The analyses of xylem ultrastructure revealed a complex, synchronized trait covariation and tradeoffs with increasing height in E. Grandis.
Anatomical traits related to xylem vessels and those related to the architecture of pit membranes were found to increase efficiency and apical dominance of water transport.
This study underlines the importance of studying tree hydraulic functioning at the organismal scale.
The results presented here will improve the understanding of height-dependent structure-function patterns in tall trees.
Keywords: Eucalyptus Grandis, hydraulic conductivity, inter vessel pit membranes, light and electron microscopy, stem water potential, tree height, tree water use, vessel anatomy, vessel taper, whole-tree assessment, xylem.