Functional Convergence and Constraints in Regulation of Transpiration and Carbon Assimilation in Tropical Forest Canopy Trees

低地热带森林以其植物物种多样性，特别是树种多样性而闻名。 该项目的前提是，尽管热带森林中的树种多样性令人困惑，但在广泛的物种中也会发生类似的适应性反应。对适应性反应可能组合的限制应导致与碳同化和蒸腾调节有关的基本植物性状之间的趋同，这是两个基本过程。 与此相一致的是，PI先前使用史密森热带研究所（STRI）在巴拿马的树冠起重机，在从单叶到整棵树的多个尺度上同时测量用水量，揭示了不同树种之间蒸腾调节的功能趋同程度令人惊讶。研究所正在建立在研究所以前的观察基础上，以确定树木结构和大小在多大程度上控制了蒸腾作用和碳同化作用的叶水平调节。 在足够的尺度范围内表征植物行为的问题对于大型森林冠层树木特别严重。树冠起重机的出现彻底改变了对森林树冠树木所有部分的访问，从树干到中间树枝，再到树冠上部的叶子。 因此，PI正在利用STRI树冠起重机提供的独特机会，将大型树木作为整体生物进行研究。 我们的主要目标之一是确定适当的数值缩放因子，树木的生理行为，树木的建筑特征，如叶面积边材面积的比例。这些比例因子将检测不同树种之间在碳吸收调节以及水分吸收、运输和损失方面的功能趋同。 揭示功能趋同领域的比例因子的发展将提供新的见解，这将大大简化这些复杂的，物种丰富的森林中的树，林分和生态系统水平的响应的解释和建模。 此外，类似的功能限制适用于广泛的物种之间的权衡有关的结构和功能的基本植物性状的示范可能有助于移动生态科学对植物物种之间的差异和相似性的性质的新范式。 参与者希望办法、结果和一般性结论适用于广泛的自然森林和管理森林，而不仅仅是热带森林。 PI还希望这项研究的结果有助于预测不同管理做法对森林生产力和水资源利用的影响。

Lowland tropical forests are notable for their high plant species diversity, particularly tree species. This project is based on the premise that despite the bewildering diversity of tree species in tropical forests, similar adaptive responses occur across a wide range of species. Constraints on the possible combinations of adaptive responses should lead to convergence among basic plant traits related to regulation of carbon assimilation and transpiration, two fundamental processes. Consistent with this, the PIs prior use of the Smithsonian Tropical Research Institute (STRI) canopy crane in Panama to make concurrent measurements of water use at multiple scales from single leaf to whole tree, has revealed a surprising degree of functional convergence in regulation of transpiration among diverse tree species.In the current project, the PIs are building upon the PIs previous observations to determine the extent to which leaf level regulation of transpiration and carbon assimilation are governed by tree architecture and size. The problem of characterizing plant behavior over an adequate range of scale has been particularly acute with large forest canopy trees. The advent of canopy cranes has revolutionized access to all parts of forest canopy trees from their trunks, to intermediate branches, to leaves in the upper crown. The PIs are therefore taking advantage of the unique opportunity provided by the STRI canopy cranes to study large trees as whole organisms. One of our key objectives is to identify appropriate numerical scaling factors that relate tree physiological behavior to tree architectural features such as the ratio of leaf area to sapwood area. These scaling factors will detect functional convergence in regulation of carbon uptake, and the uptake, transport and loss of water among diverse tree species. Development of scaling factors that reveal areas of functional convergence will provide new insights that will greatly simplify interpretation and modeling of tree, stand and ecosystem level responses in these complex, species-rich forests. Furthermore, demonstration that similar functional constraints apply across a wide range of species leading to trade-offs among basic plant traits related to structure and function may serve to move the science of ecology towards new paradigms concerning the nature of differences and similarities among plant species. The PIs expect approaches, results and general conclusions to be applicable to a wide range of natural and managed forests, not just tropical forests. The PIs also expect the results of this research to contribute to the ability to predict the consequences of different management practices for forest productivity and utilization of water resources.