Developmental and Structural Section
Bergman, Brett A. , Ewers, Frank W. , Bobich, Edward .
Effect of Leaf Nodes on the Mechanical Properties of Stems.
The effect of leaf nodes, irrigation treatment, and season on the mechanical properties of woody stems of Juglans californica were assessed. Freshly collected stem segments approximately 160 mm in length and 10 mm in diameter with various frequencies of leaf nodes were tested with an Instron mechanical testing device. Significant inverse logarithmic correlations were found between leaf node frequency and modulus of elasticity (MOE) (R2=0.7436, 0.7019; n=14), as well as modulus of rupture (MOR) (R2=0.804, 0.6424; n=14) for both irrigated and non-irrigated trees. The ruptures occurred at nodes. Within the adult populations, leaf node frequency was left-skewed with a peak at about 31 nodes per meter. Irrigation treatments and seasonal changes in the water content of the xylem tissue had no significant effect on the biomechanics of stems. Following fire, resprouts of Juglans had stems with significantly lower leaf node frequencies and significantly higher MOE and MOR values, suggesting that nodal frequency may be as important as xylem density in determining strength. Cross-sections revealed high concentrations of unlignified parenchyma cells in the leaf gaps, interrupting the xylem cylinder, which could explain the mechanical impact of leaf nodes. The study suggests that leaf nodes could be a significant source of the variation in biomechanical strength and flexibility within populations as they represent structurally weak points in the stem.
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1 - California State Polytechnic University, Biological Sciences, 3801 West Temple Avenue, Pomona, CA, 91768, USA
Modulus of Rupture
modulus of elasticity
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Wasatch B/Cliff Lodge - Level C
Date: Tuesday, July 28th, 2009
Time: 1:45 PM