DISSERTATION RESEARCH: The Ontogeny of Defense in Tropical Rainforest Trees: Leaf Secondary Metabolites across Canopy-Understory Gradients of Resources and Stressors

这项研究的目标是研究热带森林中的空气污染如何影响植物在叶子中产生一种特殊类型的化学物质的方式。因为植物不能逃避试图吃掉它们的昆虫(“食草动物”)，它们产生这些化学物质作为一种防御手段。一家超市的香料架上只提供了一种植物防御化合物令人惊叹的多样性；数万种植物防御化合物已经被编目，还有更多的还没有描述。化学防御的多样性源于食草动物和病原体已经进化出对特定防御的抗性。因此，在所谓的进化军备竞赛中，植物不断承受着进化新防御系统的压力，而消费者则不断承受着绕过它们的压力。热带森林中植物和食草动物的多样性是地球上最高的，因此这些森林也包含最高多样性的植物化学防御也就不足为奇了。植物化学防御的多样性不仅是热带森林物种数量的产物，也被认为是产生和维持热带森林生物多样性的核心因素。因此，任何对热带森林化学景观的大规模改变都可能产生广泛的影响。空气污染，特别是臭氧污染，可能就是这样的景观改变。这项研究的重点是臭氧，它是由化石燃料燃烧或生物质燃烧产生的。在这些活动集中的热带地区，记录到的臭氧水平高于在其他生态系统中观察到的影响叶片防御化学的阈值。在温带生态系统中，臭氧污染被发现既影响叶片内防御系统的浓度，也影响草食昆虫定位适当宿主植物的能力。臭氧对某些化合物的产生和稳定性的影响比其他化合物更大，因此，在化学成分多样化的热带森林中，臭氧污染对某些植物和食草动物物种的影响可能比其他物种更大。这项研究以巴拿马运河繁忙的航运交通相邻的森林为基础，将调查一系列热带树种的防御化学如何受到环境臭氧水平的影响。具体地说，它将测试氧化应激、叶片次生代谢物和食草动物是如何相互作用的。它将通过绘制森林中的臭氧水平图，并进行2x2因子臭氧和光操纵实验来评估这些变量如何影响叶片次生代谢物的产生。

This goal of this study is to examine how air pollution in a tropical forest affects the way in which plants produce a special class of chemicals in their leaves. Because plants cannot run from the insects seeking to eat them ("herbivores"), they produce these chemicals as a means of defense. The spice rack at a supermarket offers but a taste of the staggering diversity of plant defense compounds; tens of thousands have been cataloged, with many more still undescribed. The variety of chemical defenses arises from the fact that herbivores and pathogens have evolved resistance to particular defenses. Thus in what has been called an evolutionary arms-race, plants are constantly under pressure to evolve new defenses, while consumers are constantly under pressure to get around them. Tropical forests contain the highest diversity of plants and herbivores on the planet, so it is no surprise that these forests also contain the highest diversity of plant chemical defenses. Not just an artifact of the number of species in tropical forests, the diversity of plant chemical defenses is thought to be a central factor in both producing and maintaining tropical forest biodiversity. Thus, any large-scale alteration of the chemical landscape of a tropical forest may have wide-ranging effects.Air pollution, particularly ozone pollution, may constitute just such a landscape alteration. The focus of this study is ozone, which is produced as a result of fossil fuel combustion or biomass burning. In areas of the tropics where these activities are concentrated, ozone levels have been recorded above thresholds for impacts on leaf defense chemistry observed in other ecosystems. In temperate ecosystems, ozone pollution has been found to affect both the concentrations of defenses within leaves and the ability of herbivorous insects to locate appropriate host plants. Ozone affects the production and stability of certain chemical compounds more than others, so ozone pollution in a chemically diverse tropical forest is likely to affect some plant and herbivore species more than others. Based in a forest adjacent to the heavy shipping traffic of the Panama Canal, this study will investigate how the defense chemistry of an array of tropical tree species is affected by ambient ozone levels. Specifically, it will test how oxidative stress, foliar secondary metabolites, and herbivory interact. It will do so by mapping ozone levels in a forest and conducting a 2x2 factorial ozone and light manipulation experiment to assess how these variables affect production of foliar secondary metabolites.