Niklas Karl J
Section of Plant Biology, Cornell University, 14853, Ithaca, NY, USA.
Oecologia. 1992 Jul;90(4):518-526. doi: 10.1007/BF01875445.
Computer simulations were used to assess the influence of palmate leaf morphology, decussate phyllotaxy, and the elastic moduli of petioles on the capacity of turgid and wilted twigs ofAesculus hippocastanum to intercept direct solar radiation. Leaf size, morphology, orientation, and the Young's and shear moduli (E and G) of petioles were measured and related to leaf position on 8 twigs whose cut ends were placed in water ("turgid" twigs) and 8 twigs dried for 8 h at room temperature ("wilted" twigs). Petioles mechanically behaved as elastic cantilevered beams; the loads required to shear petioles at their base from twigs were correlated with the cross-sectional areas of phyllopodia but not with petiole length or tissue volume. Empirically determined morphometric and biomechanical data were used to construct "average" turgid and wilted twigs. The diurnal capacity to intercept direct sunlight for each was simulated for vertically oriented twigs for 15 h of daylight, 40° N latitude. The daily integrated irradiance (DII) of the wilted twig was roughly 3% less than that of the otherwise comparable twig bearing turgid leaves. Simulations indicated that the orientation of turgid leaves did not maximize DII. More decumbent (wilted) petioles increased DII by as much as 4%. Reduction in the girth, E, or G of petioles, or an increase in petiole length or the surface area of laminae (with attending increase in laminae weight), increased petiolar deflections and DII. Thus, the mechanical design of petioles ofA. hippocastanum was found not to be "economical" in terms of investing biomass for maximum light interception.
利用计算机模拟评估七叶树掌状叶形态、交互对生叶序以及叶柄弹性模量对七叶树嫩枝在挺直和萎蔫状态下拦截太阳直射辐射能力的影响。对8根嫩枝（其切口端置于水中，即“挺直”嫩枝）和8根在室温下干燥8小时的嫩枝（“萎蔫”嫩枝）上的叶片大小、形态、方向以及叶柄的杨氏模量和剪切模量（E和G）进行了测量，并将其与叶片位置相关联。叶柄在力学上表现为弹性悬臂梁；从嫩枝基部剪断叶柄所需的载荷与叶鞘的横截面积相关，但与叶柄长度或组织体积无关。根据经验确定的形态测量和生物力学数据构建了“平均”挺直和萎蔫嫩枝。针对北纬40°、日照15小时的垂直定向嫩枝，模拟了二者每日拦截直射阳光的能力。萎蔫嫩枝的日积分辐照度（DII）比带有挺直叶片的可比嫩枝大约低3%。模拟表明，挺直叶片的方向并非使DII最大化。更多下弯（萎蔫）的叶柄可使DII增加多达4%。叶柄周长、E或G的减小，或叶柄长度或叶片表面积的增加（伴随叶片重量增加），会增加叶柄的挠度和DII。因此，就为实现最大光拦截而投入生物量而言，七叶树叶柄的机械设计并不“经济”。
