Langer Max, Kelbel Mark C, Speck Thomas, Müller Claas, Speck Olga
Plant Biomechanics Group @ Botanic Garden, University of Freiburg, Freiburg, Germany.
Cluster of Excellence livMatS @ FIT - Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Freiburg, Germany.
Front Plant Sci. 2021 Nov 11;12:765605. doi: 10.3389/fpls.2021.765605. eCollection 2021.
From a mechanical viewpoint, petioles of foliage leaves are subject to contradictory mechanical requirements. High flexural rigidity guarantees support of the lamina and low torsional rigidity ensures streamlining of the leaves in wind. This mechanical trade-off between flexural and torsional rigidity is described by the twist-to-bend ratio. The safety factor describes the maximum load capacity. We selected four herbaceous species with different body plans (monocotyledonous, dicotyledonous) and spatial configurations of petiole and lamina (2-dimensional, 3-dimensional) and carried out morphological-anatomical studies, two-point bending tests and torsional tests on the petioles to analyze the influence of geometry, size and shape on their twist-to-bend ratio and safety factor. The monocotyledons studied had significantly higher twist-to-bend ratios (23.7 and 39.2) than the dicotyledons (11.5 and 13.3). High twist-to-bend ratios can be geometry-based, which is true for the U-profile of x with a ratio of axial second moment of area to torsion constant of over 1.0. High twist-to-bend ratios can also be material-based, as found for the petioles of with a ratio of bending elastic modulus and torsional modulus of 64. The safety factors range between 1.7 and 2.9, meaning that each petiole can support about double to triple the leaf's weight.
从力学角度来看，叶片的叶柄面临相互矛盾的力学要求。高抗弯刚度可确保叶片得到支撑，而低抗扭刚度则能保证叶片在风中的流线型。抗弯刚度与抗扭刚度之间的这种力学权衡由扭转与弯曲比来描述。安全系数描述了最大承载能力。我们选择了四种具有不同体型（单子叶植物、双子叶植物）以及叶柄和叶片空间构型（二维、三维）的草本植物，并对叶柄进行了形态解剖学研究、两点弯曲试验和扭转试验，以分析几何形状、尺寸和形状对其扭转与弯曲比及安全系数的影响。所研究的单子叶植物的扭转与弯曲比（23.7和39.2）显著高于双子叶植物（11.5和13.3）。高扭转与弯曲比可能基于几何形状，对于x的U型轮廓而言确实如此，其轴向惯性矩与扭转常数之比超过1.0。高扭转与弯曲比也可能基于材料，如对于其叶柄而言，弯曲弹性模量与扭转模量之比为64时就是如此。安全系数在1.7至2.9之间，这意味着每个叶柄能够支撑大约为叶片重量两倍至三倍的重量。
