Modeling Leaf-Sheath Interactions in Grasses
Many grains and grasses share a common architecture consisting of a central stalk which is
periodically segmented by nodes (see Figures 1 and 3) [1]. The region between two nodes is
called the internode. Leaves originate just below each node, and wrap tightly around the stalk
[2]. This portion of the leaf is referred to as the leaf sheath.
Above the sheath, a “collar” is formed at which point the
leaf blade extends from the stalk [3].
Plant growth occurs in special regions above each node
referred to as intercalary meristems [4]. In these
regions, tissues are not fully lignified and therefore have
lower strength as compared to mature stalk tissues [5].
It has been hypothesized that during stages of rapid stalk
growth (cell elongation) the leaf sheath is the primary
load-bearing member of the plant in the meristematic tissue
region. As the stalk tissues mature, structural loads become
more evenly distributed between the leaf sheath and the
stalk. At full maturity, the stalk is hypothesized to be the
primary structural member with the leaf sheath providing
relatively little structural support. Agronomists have
reported that the elongation of the stalk leads to slippage
Typical grass architecture. Stalk
between the sheath and the stalk. This slippage can
shown in white and leaf in gray.
sometimes result in an audible noise, leading to the saying
amongst farmers, “on a still night, you can hear the corn growing.”
The purpose of this research is to gain understanding about the stalk/sheath interactions
through modeling. We seek answers to the following questions:
• Can we create a very simple (1D) model of stalk/sheath slippage? If so, what
parameters does the model contain, and what are their physical counterparts?
• Can we create a 2D model of stalk/sheath interactions? What are the parameters
and their physical counterparts?
• Can we create a 3D model, etc.?
• How can surface roughness measurements be used to inform these models?
• Is there reason to believe that friction between these surfaces is directionally
dependent?
• Can the 2D and 3D models be modified to address a stalk under bending loads?
• Does the degree of friction between the sheath and stalk affect plant structural
capacity?
Data to be provided:
• Stalk geometry: detailed CT data on over 1000 individual stalks, and reliable
methods for extracting geometric features of the stalk; ranges for sheath
geometry.
• Surface roughness: preliminary data on surface roughness of the stalk and
sheath, including data from corresponding sections of the stalk/sheath interface
Maize sheath/stalk biomechanics
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References
1. Sharman, B., Developmental Anatomy of the Shoot of Zea mays L. Annals of Botany, 1942.
VI(22): p. 245-282
2. Niklas, K.J., The Mechanical Roles of Clasping Leaf Sheaths: Evidence fromArundinaria
técta(Poaceae) Shoots Subjected to Bending and Twisting Forces. Annals of Botany, 1998. 81(1):
p. 23-34.
3. Esau, K., Ontogeny of the vascular bundle in Zea Mays. Hilgardia, 1943. 15(3): p. 325-368.
4. Freeling, M. and B. Lane, The Maize Leaf, in The Maize Handbook, M. Freeling and V. Walbot,
Editors. 1994, Springer New York. p. 17-28.
5. Unpublished data, Douglas Cook, New York University Abu Dhabi.
Maize sheath/stalk biomechanics
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