Date of Award

Spring 2008

Document Type

Restricted Thesis

Terms of Use

© 2008 Jacob Brunkard. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Biology Department

First Advisor

José-Luis Machado

Abstract

Recent ecological studies have attempted to develop plant leaf economic models that describe the relationship among several functional and structural traits of leaves as a way of understanding biodiversity. This study used light-response curves, leaf mass to area ratios, a census of leaf ages, and architectural data to illustrate the plastic ontogenetic responses of four neotropical shade-tolerant species to sunny and shady light environments. Using YPlant, a computer functional-structural plant modeling system that simulates interactions among leaf physiology, above-ground plant architecture, and light environment, this study then simulated changes in self-shading and daily whole-plant carbon assimilation for individuals from these four species growing under a thick forest canopy, and estimated the percentage of carbon assimilates devoted to leaf construction and the days required for a leaf to "payback" the costs of its construction. Shade-tolerant plants exhibited architectural plasticity, lower E_{A}, lower leaf A_{max}, lower rates of decline in leaf Amax with leaf age, higher leaf lifespan, and lower LMA in the shady plots, with some variation among the species. Between 2004 and 2005, all trees produced at least one new leaf, and daily whole-plant carbon assimilation increased in spite of declining A_{max} in older leaves. Daily carbon assimilation per leaf area was also positively correlated with low self-shading, which was architecturally regulated by plants despite differences in species morphology. This study concludes that accurate models of leaf economics for young shade-tolerant plants should include the complex interactions among functional traits, structural traits, and environmental conditions of whole-plants that can be simulated with YPlant and similar computer models.

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