Effects of Past Vegetation Change on Soil formation near the Prairie-Forest Vegetation Border with Implications for the Future

这个项目将研究森林和草原植被对富含粘土的地下土层发育的影响，这些土层通常是由土壤中渗入的水将粘土带到下面形成的。粘粒在底土中的积累强烈影响植物养分和水分的有效性以及污染物的滞留。了解影响表土和底土粘粒含量强烈差异形成的因素，以及这种差异发展的速度有多快，是土壤形成研究中一个基本的、长期存在的问题。在美国中西部，在自然植被为森林的地方，粘土含量的表土-底土对比要比草原强得多。这个项目将重点放在明尼苏达州的一个地区，以前的研究已经记录了过去10,000年来森林-草原边界的重大变化。通过分析不同时期森林影响下形成的土壤，从一万多年到几百年，这项研究将检验这样一个假设，即土壤中大多数向下移动的粘土在森林取代草原等条件变化后迅速发生。仍然对森林-草原边界最近的变化做出反应的土壤将被用来检验第二个假设，即从草原植被添加到土壤中的有机物限制粘土的移动，随着森林入侵草原，粘土被释放出来向下移动。碳同位素分析将用于检测过去草原草添加到土壤中的有机质。在同一研究区域深入研究过去植被和气候变化的生态学家将对该项目的结果产生极大的兴趣。与之前基于湖泊沉积物证据的工作相比，土壤可能提供更多关于植被变化的特定地点信息。总体而言，该项目将对过去的环境如何影响土壤形成产生重要的新见解，这也可能有助于预测土壤对当前或未来环境变化的反应。该项目涉及大量的实地调查，以及各种不同的实验室分析，包括先进的技术，如有机物质组分的同位素分析。因此，它特别适合提供丰富的本科生研究经验，这一目标在科学教育中越来越被优先考虑。两名本科生将致力于该项目的各个方面，其中至少有一人是通过威斯康星大学麦迪逊分校针对代表性不足群体的项目招募的。一名研究生也将参与这个项目，完成一篇关于相关主题的论文。该项目将加强更广泛的自然地理学领域的教育和研究，该领域寻求对气候、生物过程、土壤和地貌的综合了解。土壤和植被之间的关系在许多自然地理学入门高级课程中都有讲授，包括威斯康星大学麦迪逊分校开设的那些课程。该项目将提供一个数据丰富的案例研究，以说明这些关系的具体细节，并将它们与过去植被变化的研究联系起来，这是当今自然地理学的一个主要研究课题。

This project will study the influence of forest and prairie vegetation on the development of clay-rich subsoil horizons, often formed when clay is carried downward by water percolating through the soil. Accumulation of clay in the subsoil strongly influences the availability of nutrients and water for plants and retention of contaminants. Understanding the factors that influence development of strong contrasts in clay content between topsoil and subsoil, and how rapidly those contrasts can develop, is a basic, long-standing problem in research on soil formation. In the Midwestern U.S., much stronger topsoil-subsoil contrasts in clay content are found where the natural vegetation was forest than where it was prairie. This project will focus on that vegetation effect, in an area of Minnesota where previous research has documented major shifts in the forest-prairie boundary over the past 10,000 years. By analyzing soils that have formed under the influence of forest for varying periods of time, from more than 10,000 years to a few hundred years, this study will test the hypothesis that most downward clay movement in soils occurs rapidly after a change in conditions such as forest replacing prairie. Soils that are still responding to recent shifts in the forest-prairie boundary will be used to test a second hypothesis, that organic matter added to the soil from prairie vegetation limits clay movement, and clay is released to move downward as forest invades the prairie. Carbon isotope analysis will be used to detect organic matter added to the soil in the past by prairie grasses. The project results will be of great interest to ecologists who have intensively studied past vegetation and climate change in the same study area. Soils can potentially provide much more site-specific information on vegetation change than previous work based on evidence from lake sediments. Overall, the project will produce important new insight on how past environments influenced soil formation, which may also help predict soil response to current or future environmental changes. The project involves considerable field investigation, as well as highly varied lab analyses including advanced techniques such as isotopic analysis of organic matter fractions. Therefore, it is especially well-suited to provide rich undergraduate research experience, a goal that is increasingly prioritized in science education. Two undergraduate students will work on all aspects of the project, at least one of them recruited through a University of Wisconsin-Madison program directed toward underrepresented groups. A graduate student will also work on the project, completing a thesis on a related topic. The project will enhance both education and research in the broader field of physical geography, which seeks an integrated understanding of climate, biological processes, soils, and landforms. Relationships between soils and vegetation are taught in many introductory to advanced courses in physical geography, including those offered at UW-Madison. This project will provide a data-rich case study to illustrate specific details of those relationships and also link them to research on past vegetation change, a major research topic in physical geography today.