Almeras Tancrede, Costes Evelyne, Salles Jean-Claude
UMR 1098 Biologie du développement des Espèces Pérennes Cultivées, INRA-ENSAM-IRD-CIRAD, Equipe 'Architecture et Fonctionnement des Espèces Fruitières', 2 Place Viala, 34060 Montpellier Cedex 1, France.
Ann Bot. 2004 Apr;93(4):455-68. doi: 10.1093/aob/mch054. Epub 2004 Feb 23.
Stem shape in angiosperms depends on several growth traits such as elongation direction, amount and position of axillary loads, stem dimensions, wood elasticity, radial growth dynamics and active re-orientation due to tension wood. This paper analyses the relationship between these biomechanical factors and stem shape variability.
Three apricot tree varieties with contrasting stem shape were studied. Growth and bending dynamics, mechanical properties and amount of tension wood were measured on 40 1-year-old stems of each variety during one growth season. Formulae derived from simple biomechanical models are proposed to quantify the relationship between biomechanical factors and re-orientation of the stems. The effect of biomechanical factors is quantified combining their mechanical sensitivity and their actual variability.
Re-orientations happened in three main periods, involving distinct biomechanical phenomena: (a) passive bending due to the increase of shoot and fruit load at the start of the season; (b) passive uprighting at the fall of fruits; (c) active uprighting due tension wood production at the end of the season. Differences between varieties mainly happened during periods (a) and (b).
The main factors causing differences between varieties are the length/diameter and the load/cross-sectional area ratios during period (a). Wood elasticity does not play an important role because of its low inter-variety variability. Differences during period (b) are related to the dynamics of radial growth: varieties with early radial growth bend weakly upward because the new wood layers tend to set them in a bent position. The action of tension wood during period (c) is low when compared with passive phenomena involved in periods (a) and (b).
被子植物的茎干形状取决于多种生长特性，如伸长方向、腋生负荷的数量和位置、茎干尺寸、木材弹性、径向生长动态以及由于拉力木导致的主动重新定向。本文分析了这些生物力学因素与茎干形状变异性之间的关系。
研究了三种茎干形状不同的杏树品种。在一个生长季节中，对每个品种的40根1年生茎干测量其生长和弯曲动态、力学性能以及拉力木的数量。提出了从简单生物力学模型推导的公式，以量化生物力学因素与茎干重新定向之间的关系。结合生物力学因素的力学敏感性及其实际变异性，对其影响进行了量化。
重新定向发生在三个主要时期，涉及不同的生物力学现象：（a）季节开始时由于新梢和果实负荷增加导致的被动弯曲；（b）果实掉落时的被动直立；（c）季节结束时由于拉力木产生导致的主动直立。品种间的差异主要发生在（a）和（b）时期。
导致品种间差异的主要因素是时期（a）的长度/直径和负荷/横截面积比。木材弹性由于品种间变异性低，作用不显著。时期（b）的差异与径向生长动态有关：径向生长早的品种向上弯曲较弱，因为新的木质层倾向于使其处于弯曲位置。与时期（a）和（b）中的被动现象相比，时期（c）中拉力木的作用较小。
