Coordination of Leaf Physiology and Morphology with Variations in Resources Available to Two Neotropical Tree Species

我们建议检验这样一种假设，即在水分和光照的季节性限制下，植物资源被分配来最大化碳收益和生产力。寿命、单位面积质量、氮素浓度、单位植物质量面积、基于面积的建设成本和叶片的同化能力将被视为巴拿马旱季和雨季生产力(相对增长率)的决定因素。这些功能被假设为相互支持、相互依赖和随意相互关联。叶片特征的变化将被记录在成熟的常绿热带树种的树冠内的光梯度上，以及这些物种的苗木之间，在一个实验的普通花园中，采用光和水水平对比的析因设计。这些树种在叶片寿命上有相当大的差异，同时在水和光可获得性不同的季节产生新叶。因此，它们允许检查关于功能特性如何随着碳获取机会的变化而变化的具体预测。研究将在史密森热带研究所(STRI)进行，使用一台建筑起重机进入热带干燥森林的树冠。园艺处理和郁闭树将被跟踪三年。这将是第一个关于树冠内生理变化的全面数据，也是第一个热带树种树苗和树冠树叶寿命和功能的比较。这些研究将展示选择在叶片性状之间产生对资源的短期和长期变异的协调反应的潜力。如果这些特征之间的功能关系被证明是紧密协调的，那么这种生理综合征将在叶片和整个植物的生长和繁殖过程之间提供经验上的联系。热带树木的树冠提供了一些已知的关于光、湿度、叶水、可能还有养分的最陡峭的资源梯度，因此是评估功能特征之间关系的模型系统。由于对热带森林砍伐的高度关注，迫切需要了解与能够快速再生的物种相关的生理症状。

We propose to examine the hypothesis that plant resources are allocated to maximize carbon gain and productivity under the constraints imposed by the seasonality of moisture and irradiance. Lifespan, mass per area, nitrogen concentration, area per plant mass, area-based construction costs, and assimilation capacity of leaves will be examined as determinants of productivity (relative growth rate) during the dry season and wet season in Panama. These features have been hypothesized to be mutually supporting, interdependent, and casually interrelated. Variation in leaf features will be documented over light gradients within the canopies of mature evergreen tropical species, and among seedlings of these species in an experimental common garden with a factorial design of contrasting levels of light and water. These species encompass considerable variation in leaf longevity, while producing new leaves in seasons of contrasting water and light availability. As such they allow the examination of specific predictions about how functional characters vary in response to variation in the opportunity for carbon gain. Studies will be conducted at the Smithsonian Tropical Research Institute (STRI) using a construction crane for access to the canopy of a tropical dry forest. Garden treatments and canopy trees will be followed for three years. These will be the first comprehensive data for within-canopy physiological variation, and the first comparison of seedlings and canopy trees for leaf longevity and function in tropical species. These studies will demonstrate the potential for selection to produce coordinated responses among leaf characters to short-term and long-term variation in resources. If functional relationships among these features prove to be tightly coordinated, such physiological syndromes will provide an empirical link between leaf and whole-plant processes of growth and reproduction. The canopies of tropical trees provide some of the steepest resource gradients known with respect to light, humidity, leaf water, and possibly nutrient, and thus are a model system to assess the relationships among functional characteristics. Because of the great concern over tropical deforestation, there is a pressing need to understand physiological syndromes associated with species capable of rapid regeneration.