CAREER: Ecosystem Change in Forests and Grasslands from Decades to Millennia: A Retrospective Approach

肯德拉·k·麦克劳克兰堪萨斯州立大学氮循环是地球上最关键的生物地球化学循环之一，因为氮可以潜在地施肥和危害生态系统。然而，我们对森林和草地生态系统氮有效性的长期模式知之甚少，这限制了我们理解生态系统功能近期变化和预测未来功能的能力。该研究项目将详细调查全新世（过去1万年）北美中部三个地点的营养循环变化。该研究将检查三个地点的植被历史对比，以重建过去氮循环和其他生态系统特性的变化。特别是，研究人员将获得过去在三个地点测量10年、100年、1000年和1万年变化的记录：一个草原地点、一个森林地点和一个在全新世期间在森林和草原之间过渡的地点。在每个地点，研究人员将在取自小湖泊的沉积物岩心中测量一些东西（包括稳定的氮和碳同位素、花粉、木炭和选定的元素浓度）。此外，将获得森林流域活树的木材历史和草地附近植物标本室保存的叶子的区域化学记录。该项目有四个主要目标：1)在多个地点重建全新世时间尺度上陆地氮循环的发展；2)评估植被、气候变化和干扰作为生物地球化学循环驱动因素在几十年到几千年时间尺度上的相对作用；3)在景观尺度上改进沉积物、木材和叶片组织中稳定氮同位素的解释。4)形成一套可供其他研究人员使用的技术，以确定当前人类引起的全球氮循环变化是增加还是减少了氮的可用性。该项目产生的经验记录将提供全新世氮循环的第一个见解，并允许评估20世纪人类引起的氮沉积对草地和森林生态系统的相对影响。这项研究将确定使系统易受或抵抗氮污染的生态系统特征，特别是在植被类型（草地或森林）重要的情况下。它还提供了与政策相关的理解，即氮是一种潜在的污染物，其沉积的调节成本很高。该研究提供了一个新的视角：回顾方法来理解现代全球变化，加强观察和实验方法。这项研究将提供历史在确定急性和慢性压力源对生态系统的影响方面的作用的清晰图景，对氮排放具有重要意义。除了科学进步之外，该项目还将帮助培养下一代科学家，包括中学生、本科生和研究生。最后，研究成果将在美国明尼苏达州伊塔斯卡州立公园的游客中心设计展览和教育材料，直接向公众展示。

NATIONAL SCIENCE FOUNDATIONABSTRACTBCS - 0955225 Kendra K. McLauchlanKansas State University The nitrogen (N) cycle is one of the planet's most critical biogeochemical cycles because N can potentially both fertilize and harm ecosystems. However, the long-term patterns of N availability in forest and grassland ecosystems are poorly understood, limiting our ability both to understand recent changes in ecosystem function and to predict future functioning. This research project will investigate changes in nutrient cycles at three sites in mid-North America in great detail during the Holocene (past 10,000 years). The research will examine contrasts in vegetation history among three sites to reconstruct past changes in N cycling and other ecosystem properties. In particular, the researchers will obtain past records that measure changes that take 10, 100, 1,000, and 10,000 years at three sites: one prairie site, one forest site, and one site that transitioned between forest and prairie during the Holocene. At each site, the researchers will measure several things (including stable N and carbon isotopes, pollen, charcoal, and selected elemental concentrations) in sediment cores taken from small lakes. Additionally, both histories in wood from living trees in the forested watersheds and a regional record of foliar chemistry from leaves preserved in herbaria near the grassland site will be obtained. The project has four main goals: 1) reconstruct the development of terrestrial N cycles over Holocene timescales at multiple sites, 2) evaluate the relative roles of vegetation, climate change, and disturbances as drivers of biogeochemical cycles on timescales from decades to millennia, 3) improve interpretations of stable N isotopes in sediment, wood, and leaf tissue on the landscape-scale, and 4) formalize a set of techniques that can be used by other researchers to determine if current human-caused changes to the global N cycle are increasing or decreasing N availability.The empirical records generated in this project will provide the first insights on Holocene N cycling as well as allow evaluation of the relative impact of human-caused N deposition on grassland and forested ecosystems in the 20th century. The research will identify ecosystem characteristics that make systems vulnerable or resistant to N pollution, particularly if the vegetation type (grassland or forest) matters. It also provides policy-relevant understanding regarding N as a potential pollutant whose deposition would be expensive to regulate. The research provides a new perspective: the retrospective approach to understanding modern global change, strengthening observational and experimental approaches. The research will provide a clear picture of the role of history in determining the effects of acute and chronic stressors on ecosystems, with important implications for N emissions. In addition to the scientific advances, the project will help train the next generation of scientists, including middle school, undergraduate, and graduate students. Finally, research results will be brought directly to the public by designing an exhibit and educational materials at the Visitors Center at Itasca State Park, Minnesota, USA.