Kaminski Ruwen, Speck Thomas, Speck Olga
Plant Biomechanics Group, Botanic Garden, Faculty of Biology, University of Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany.
Competence Network Biomimetics, Baden-Württemberg, Schänzlestraße 1, 79104 Freiburg, Germany.
Am J Bot. 2017 Aug;104(8):1157-1167. doi: 10.3732/ajb.1700110.
Plant stems can be regarded as fiber-reinforced structures characterized by anatomical heterogeneity, mechanical anisotropy, and adaptability to changing internal and external constraints. Our study focused on adaptive spatiotemporal changes in morphology, anatomy, and mechanical properties during the ontogeny of Leonurus cardiaca L. (Lamiaceae) internodes, proving considerable functional adaptability.
Four-point bending tests and torsional tests were carried out on the same internodes to measure flexural and torsional stiffness. Axial and polar second moments of area for entire cross sections and for individual tissues were determined from transverse stem sections immediately after testing. Based on these data, additional relevant mechanical parameters such as bending elastic modulus, torsional modulus and twist to bend ratio were calculated.
Leonurus cardiaca is characterized by a square-shaped hollow stem in transverse section with an outer frame of various strengthening tissues and an inner ring of parenchyma. Statistical analyses of axial and polar second moment of area, flexural stiffness, torsional stiffness, bending elastic modulus, and torsional modulus revealed significant differences for all comparisons with respect to spatial resolution (two adjacent internodes) and temporal resolution (in June before flowering and in September after fruit formation). The twist to bend ratios of the internodes, however, always remain in the same range.
With respect to spatiotemporal development, stems of the subshrub L. cardiaca show a marked increase in flexural and torsional stiffness during ontogeny. Strikingly, changes in stem mechanics are more influenced by variations in mechanical tissue properties than by changes in relative proportion of different tissue types.
植物茎可被视为纤维增强结构，其特点是具有解剖学异质性、力学各向异性以及对内部和外部变化约束的适应性。我们的研究聚焦于益母草（唇形科）节间个体发育过程中形态、解剖结构和力学性能的适应性时空变化，结果表明其具有相当强的功能适应性。
对同一节间进行四点弯曲试验和扭转试验，以测量弯曲刚度和扭转刚度。在试验结束后，立即从茎的横向切片中确定整个横截面以及各个组织的轴向和极惯性矩。基于这些数据，计算出其他相关力学参数，如弯曲弹性模量、扭转模量和扭转与弯曲比。
益母草的茎在横切面上呈方形中空，外部有各种强化组织构成的框架，内部有一圈薄壁组织。对轴向和极惯性矩、弯曲刚度、扭转刚度、弯曲弹性模量和扭转模量进行统计分析后发现，在空间分辨率（两个相邻节间）和时间分辨率（开花前的6月和果实形成后的9月）的所有比较中均存在显著差异。然而，节间的扭转与弯曲比始终保持在同一范围内。
就时空发育而言，亚灌木益母草的茎在个体发育过程中弯曲刚度和扭转刚度显著增加。值得注意的是，茎力学性能的变化更多地受机械组织特性变化的影响，而非不同组织类型相对比例的变化。
