Dense but flexible wood-How leaf nodes impact xylem mechanics in Juglans californica

Brett A. Bergman, Edward G. Bobich, Stephen D. Davis, Yasuhiro Utsumi, Frank W. Ewers

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

A node is the point of attachment of the leaf to the stem of a plant; gaps associated with nodes have been viewed as discontinuities of the stem vascular system. We tested the hypothesis that the node/gap is a spring-like joint that impacts stem flexibility even well after the leaves have been shed, with some stems specialized for elongation and others for flexibility. Four-point bending tests were done using an Instron Mechanical Testing Device with the independent variable being the number of nodes in the stem segment and dependent variables being Modulus of Elasticity (MOE), Modulus of Rupture (MOR), and xylem density. Node anatomy was examined microscopically to assess structure and function. The stiffness of the stem was inversely proportional to the frequency of leaf nodes. Surprisingly, xylem density was inversely proportional to the frequency of leaf nodes in stems of adult trees. The tissue around nodes/gaps consisted of twisted and contorted cells that may be effective at absorbing compressive and tensile stresses. Because nodes behave as spring-like joints, the frequency of nodes relates to function, with some stems specialized for vertical expansion and others for light capture and damping of wind stress. The ultimate stems on a tree are the most bendable, which may allow the trees to avoid breakage.

Original languageEnglish
Pages (from-to)372-381
Number of pages10
JournalIAWA Journal
Volume39
Issue number4
DOIs
Publication statusPublished - 2018

All Science Journal Classification (ASJC) codes

  • Forestry
  • Plant Science

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