Beyschlag Joachim, Zotz Gerhard
Carl von Ossietzky University Oldenburg, Institute for Biology and Environmental Sciences, Functional Ecology, Box 2503, D-26111 Oldenburg, Germany.
Smithsonian Tropical Research Institute, Apartado Postal 08343-03092, Panama, Republic of Panama.
Ann Bot. 2017 Nov 10;120(5):681-692. doi: 10.1093/aob/mcx048.
The functional relevance of heteroblasty, an abrupt morphological change in the ontogeny of a considerable number of angiosperm species, is still largely unresolved. During the ontogeny of many epiphytic Tillandsioids (Bromeliaceae), such a change occurs when small individuals transform into larger, tank-forming individuals that are capable of external water storage. Apart from its fundamental effect on plant water relations, the associated transition from narrow to broader leaves also affects plant architecture. The morphological changes and their effect on light interception may be especially relevant for heteroblastic species in the moist understorey, which are expected to be limited primarily by light.
A functional structural plant model (Yplant) was used to construct digital replicas of atmospheric and tank-forming individuals of four species, two of them naturally growing in exposed conditions and two occurring in understorey sites. This allowed the determination of leaf display efficiencies as well as a systematic analysis of leaf architectural traits and their effect on light interception.
Modifying existing plant morphologies showed that broader leaves cause more self-shading within the plant. This supports the hypothesis that species from the light-limited understorey benefit from the early atmospheric life form through increased light capture. Modelling plant morphology that continuously followed the ontogenetic trajectories of the leaf architectural traits revealed that the rising total leaf number in atmospheric individuals constantly increased self-shading. Therefore, at a certain ontogenetic stage, a tipping point was reached when the tank form was even favourable in terms of light capture as it was associated with fewer leaves.
The effects of changes in leaf morphology and leaf architecture on plant light capture may explain the common occurrence of heteroblastic species in the understorey of Neotropical forests, which does not negate a simultaneous positive effect of heteroblasty on plant water relations.
许多被子植物物种个体发育过程中会出现突然的形态变化，即异形叶性，其功能相关性在很大程度上仍未得到解决。在许多附生铁兰属植物（凤梨科）的个体发育过程中，当小个体转变为能够进行外部储水的较大的莲座状个体时，就会发生这种变化。除了对植物水分关系产生根本影响外，从窄叶到宽叶的相关转变也会影响植物结构。形态变化及其对光截获的影响对于潮湿林下的异形叶性物种可能尤为重要，预计这些物种主要受光照限制。
使用功能结构植物模型（Yplant）构建了四个物种的气生型和莲座状个体的数字模型，其中两个自然生长在开阔环境中，另外两个生长在林下环境。这使得能够确定叶片展示效率，并对叶片结构特征及其对光截获的影响进行系统分析。
对现有植物形态进行修改表明，较宽的叶片会导致植物内部更多的自遮荫。这支持了以下假设：来自光照受限林下的物种通过增加光捕获从早期的气生生活型中受益。对沿着叶片结构特征个体发育轨迹连续变化的植物形态进行建模表明，气生个体中总叶片数的增加不断增加自遮荫。因此，在某个个体发育阶段，当莲座状形态由于叶片较少在光捕获方面甚至更有利时，就达到了一个临界点。
叶片形态和叶片结构变化对植物光捕获的影响可能解释了新热带森林林下异形叶性物种的普遍存在，这并不否定异形叶性对植物水分关系同时具有的积极影响。
