Axial variation of xylem conduits in the Earth’s tallest trees

Cameron B. Williams, Tommaso Anfodillo, Alan Crivellaro, Martina Lazzarin, Todd E. Dawson, George W Koch

Research output: Contribution to journalArticle

Abstract

Key message: In the Earth’s tallest tree species, axial variation in conduit size matches theoretical predictions minimizing the accumulation of hydraulic resistance with height growth, within a constraint of maximum conduit diameter. Abstract: Hydraulic limitations to tree height can be mitigated by widening the conducting elements toward a tree’s base. However, size limits of tracheid and vessel dimensions may constrain this compensation mechanism as the water transport pathway elongates. Moreover, variation in conduit size is poorly described in tall trees even though their long transport paths have high potential for hydraulic resistance. Here, we evaluated whether axial variation in conduit diameter was uniquely structured, or matched theoretical predictions in Sequoia sempervirens, Sequoiadendron giganteum, and Eucalyptus regnans that were 86–105 m tall and exceeded 85% of the maximum height for each species. Across Sequoia and Sequoiadendron, tree top tracheids maintained constant width, whereas tree base tracheids in the outermost ring were 20% wider in taller trees, suggesting maintenance of basipetal conduit widening with height growth. In all trees, the observed widening decreased at a rate per unit path length that fitted well to a power function with an exponent consistent with hydraulic compensation. However, below about 60 m from the tree tops, conduit diameters approached an asymptote beneath the power function, indicating a limit to maximum conduit size. Quantifying the distribution of base-to-top hydraulic resistance suggested that the minimal hydraulic benefit gained with increasingly wider conduits near the tree base may trade off with other factors such as maintaining mechanical strength or reducing fluid volume. We summarize these results into an anatomical model of height growth that includes limits to axial variation in conduit diameter and is supported by many physiological and anatomical observations.

Original languageEnglish (US)
JournalTrees - Structure and Function
DOIs
StatePublished - Jan 1 2019

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Xylem
xylem
fluid mechanics
Sequoiadendron
hydraulics
Sequoia
tracheids
tree crown
Sequoiadendron giganteum
Eucalyptus regnans
Sequoia sempervirens
Growth
prediction
xylem vessels
Anatomic Models
Eucalyptus
trade-off
vessel
Maintenance

Keywords

  • Coast redwood
  • Giant sequoia
  • Hydraulic resistance
  • Metabolic scaling theory
  • Mountain ash
  • Tall trees
  • Tree height growth
  • Wood anatomy

ASJC Scopus subject areas

  • Forestry
  • Physiology
  • Ecology
  • Plant Science

Cite this

Axial variation of xylem conduits in the Earth’s tallest trees. / Williams, Cameron B.; Anfodillo, Tommaso; Crivellaro, Alan; Lazzarin, Martina; Dawson, Todd E.; Koch, George W.

In: Trees - Structure and Function, 01.01.2019.

Research output: Contribution to journalArticle

Williams, Cameron B. ; Anfodillo, Tommaso ; Crivellaro, Alan ; Lazzarin, Martina ; Dawson, Todd E. ; Koch, George W. / Axial variation of xylem conduits in the Earth’s tallest trees. In: Trees - Structure and Function. 2019.
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