Zebrowski J
Department of Genetics, Plant Breeding and Acclimatization Institute, Warsaw, Poland.
Planta. 1999 Jan;207(3):410-7. doi: 10.1007/s004250050499.
The mechanical response of cereal plant shoots to load caused by wind and gravity in the field is swaying in flexure around the vertical or near vertical transient equilibrium position determined by the stationary component of the wind pressure. The aim of this work was to characterise the kinematic and dynamic attributes and their interrelations in freely swaying inflorescence-bearing stems of wheat (Triticum aestivum L.) and Triticale. The fundamental natural frequency of the stems appeared to be considerably lower than predicted from the theory of vibration using the model of a cantilever beam oscillator and assuming the spring constant to be equal to the force-deflection ratio. Because of the rate of deformation and visco-elastic behaviour of the plant material, a discrepancy of about 10% was found between the dynamic and static stem bending resistance. The presence of the tip inflorescence caused vibrating vertical stems to behave as compressed columns in which the effective spring constant was strongly biased by the apical load due to the weight of the inflorescence. At the late milk stage, in the freely swaying stems of wheat and Triticale, the resistance to dynamic lateral loads was reduced by about 30% as a result of compression exerted by the inflorescence. So the prominent effect of the tip inflorescence on the dynamic behaviour (the effective spring constant and the natural frequency) of the stem is attributed to the non-negligible magnitude of the inflorescence weight relative to the critical load producing elastic buckling in slender vertical structures. Stem softening as a consequence of increasing inflorescence weight is assumed to be one of the essential factors reducing the lodging resistance in cereal crops at the late milk stage. The feasibility of the compressed-column approach for predicting the dynamic bending performance of slender vertical plant organs is discussed.
谷类作物茎秆在田间对风荷载和重力荷载的力学响应是围绕由风压固定分量确定的垂直或接近垂直的瞬态平衡位置发生弯曲摆动。本研究的目的是表征小麦（Triticum aestivum L.）和小黑麦自由摆动的带花序茎秆的运动学和动力学属性及其相互关系。茎秆的基本固有频率似乎远低于使用悬臂梁振荡器模型并假设弹簧常数等于力-挠度比的振动理论预测值。由于植物材料的变形速率和粘弹性行为，茎秆动态和静态抗弯能力之间存在约10%的差异。顶端花序的存在使振动的垂直茎秆表现为受压柱体，其中有效弹簧常数因花序重量产生的顶端荷载而受到强烈影响。在乳熟后期，在小麦和小黑麦的自由摆动茎秆中，由于花序施加的压力，对动态侧向荷载的抵抗力降低了约30%。因此，顶端花序对茎秆动态行为（有效弹簧常数和固有频率）的显著影响归因于花序重量相对于在细长垂直结构中产生弹性屈曲的临界荷载具有不可忽略的量级。花序重量增加导致的茎秆软化被认为是降低谷类作物乳熟后期抗倒伏能力的重要因素之一。本文还讨论了采用受压柱体方法预测细长垂直植物器官动态弯曲性能的可行性。
