Collaborative Research: Testing the Role that Biotic Interactions Play in the Latitudinal Diversity Gradient: A Chemical Community Ecology Approach to Understanding Tree Diversity

我们星球最显著的特征之一是从两极到赤道的生物多样性急剧增加。这种全局多样性梯度在树木中尤其明显。面积为0.25平方公里的林地在加拿大亚北极地区有10个树种，在美国大陆有10至70个树种，在亚马逊河流域有1 200个树种。自达尔文和华莱士以来，生物学家一直假设环境压力在温带和季节性气候中占主导地位，但温暖，潮湿，热带雨林中的植物所经历的压力主要是与其他生物体的相互作用，包括昆虫食草动物和微生物病原体。植物被认为会进化出化学防御来对抗它们的敌人，而它们的敌人也会进化出对抗这些防御的化学防御，在热带地区更快，导致热带地区植物物种之间防御化学的变化更大，最终导致物种多样性更大。由于缺乏研究植物化学惊人多样性的工具，这些想法在很大程度上没有得到大规模的测试。这项研究将克服这一历史障碍，化学生态学利用代谢组学的最新创新-生物体的化学档案的研究。科学家们将研究从亚北极加拿大到亚马逊雨林的20个长期森林地块中2,000种树木和灌木物种的化学特征或代谢组的物种差异，它们对个体树木生长和生存的影响，它们对维持多样性的贡献。该项目将资助两名博士。来自德克萨斯大学奥斯汀分校和华盛顿大学圣路易斯分校代表性不足群体的学生，本科生研究机会，以及更大研究社区的能力建设。其他更广泛的影响包括在国际会议上提供研讨会，并为研究界创建一个公开的代谢组数据库。这些数据将支持美国政府支持的国家科学基金会国家生态观测网络（氖）和史密森学会森林全球地球观测站的未来研究。研究人员将把生态代谢组学的最新创新与现有的关于森林树木群落多样性和动态的数据结合起来，这些群落跨越气候，纬度，从加拿大的北方森林（21公顷11种）到亚马逊热带雨林（25公顷1，200种）的树种多样性。该项目将利用史密森尼森林全球地球观测站（ForestGEO）和圣地亚哥动物园全球协调的20个大规模森林动态地块中3，600多个树种的生长，生存和地图分布的现有数据，以及来自13个森林地块的现有代谢组学数据。在这些数据的基础上，研究人员将收集和分析7个新森林地块中1，367个物种的叶子，这些地块代表独特的气候和/或提供关键的幼苗性能数据集。研究人员将结合联合收割机代谢组学数据，邻里人口模型和理论模拟，以确定i）叶次生化学如何塑造树木群落内的当地物种相互作用，ii）叶次生化学对当地物种相互作用的影响如何在纬度和气候梯度上变化，iii）化学介导的生态位差异在维持物种多样性方面的重要性纬度和气候梯度。最终，长期森林地块和代谢组学新技术的结合将为理解地球生物多样性的根本问题提供前所未有的范围，规模和实质性答案。除了指导本科生和研究生，研究人员还将在国际会议上领导森林代谢组学研讨会，培训学生和其他科学家收集，分析和应用代谢组学数据到社区规模的生态学。该研讨会将为来自美国和非洲，亚洲和拉丁美洲发展中国家的早期职业研究人员提供能力建设。最后，该项目将为200多个北美和2,000多个新热带树种建立一个代谢物的公共数据库，其中大部分是未充分研究的热带雨林树木。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

One of the most striking features of our planet is the dramatic increase in biodiversity from the poles to the equator. This global diversity gradient is especially noticeable among trees. Forest plots measuring 0.25 km2 contain 10 tree species in subarctic Canada, between 10 and 70 tree species in the continental United States, and 1,200 tree species in Amazonia. Since Darwin and Wallace, biologists have hypothesized that environmental stress predominates in temperate and seasonal climates, but the stresses experienced by plants in warm, wet, tropical rainforests are dominated by their interactions with other organisms, including insect herbivores and microbial pathogens. Plants are thought to evolve chemical defenses against their enemies, and their enemies to evolve counters to these defenses, more rapidly in the tropics, resulting in greater variation in defensive chemistry among plant species in the tropics, and ultimately greater species diversity. These ideas have gone largely untested at large scales because of a lack of tools to study the astonishing diversity of plant chemistry. This study will overcome this historical obstacle to chemical ecology by taking advantage of recent innovations in metabolomics—the study of the chemical profiles of organisms. The scientists will examine species differences in chemical profiles, or metabolomes, for 2,000 tree and shrub species in 20 long-term forest plots ranging from subarctic Canada to the Amazon Rainforest, their effects on the growth and survival of individual trees, their contribution to the maintenance of diversity. The project will support two Ph.D. students from underrepresented groups at the University of Texas at Austin and Washington University in St. Louis, undergraduate research opportunities, and capacity building in the larger research community. Other broader impacts include offering workshops at international meetings and the creation of a publicly available metabolome database for the research community. These data will support future research at US Government-supported sites within the National Science Foundation’s National Ecological Observatory Network (NEON) and the Smithsonian Institution’s Forest Global Earth Observatory.The researchers will couple recent innovations in ecological metabolomics with existing data on the diversity and dynamics of forest-tree communities that span large-scale gradients in climate, latitude, and tree-species diversity from boreal forest in Canada (11 species in 21 hectares [ha]) to tropical rainforest in Amazonia (1,200 species in 25 ha). This project will leverage existing data on the growth, survival, and mapped distributions of more than 3,600 tree species in 20 large-scale forest-dynamics plots coordinated by the Smithsonian Forest Global Earth Observatory (ForestGEO) and San Diego Zoo Global, as well as existing metabolomics data from 13 forest plots. Building on these data, the researchers will collect and analyze leaves of 1,367 species in 7 new forest plots that represent unique climates and/or provide key seedling performance datasets. The researchers will combine metabolomics data, neighborhood demographic models, and theoretical simulations to determine i) how leaf-secondary chemistry shapes local species interactions within tree communities, ii) how the effects of leaf-secondary chemistry on local species interactions vary across latitudinal and climatic gradients, and iii) the importance of chemically mediated niche differences in maintaining species diversity across latitudinal and climatic gradients. Ultimately, the combination of long-term forest plots and novel techniques in metabolomics will provide unprecedented answers, in scope, scale, and substance, to questions that are fundamental to understanding Earth’s biodiversity. In addition to mentoring undergrad and graduate students, the researchers will lead a forest-metabolomics workshop at international meetings to train students and other scientists in the collection, analysis, and application of metabolomic data to community-scale ecology. The workshop will provide capacity building for early-career researchers from US and developing countries in Africa, Asia, and Latin America. Finally, the project will generate a public database of metabolites for over 200 North American and over 2,000 Neotropical tree species, most of which are understudied tropical rainforest trees.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.