Dissertation Research: Reconstructing past terrestrial nitrogen cycles from chlorophyll degradation products in soil

该项目的目标是开发一种方法，重建工业化前地貌的氮循环在过去环境和生态变化期间的表现，以便更好地洞察未来可能发生的变化。过去氮素动态的变化，例如植物可以从土壤中吸收多少氮素，或者生态系统中氮素的损失是在水中还是作为气体进入大气，可以从土壤中残留的植物部分的氮同位素比率中包含的信息来推断。该项目将检查特定植物化合物在土壤中的持久性，并确定在植物残留物分解形成更稳定的土壤有机质时，它们的氮同位素比率是否保持不变。人们很好地认识到，有必要将氮的动态准确地纳入全球碳和气候模型。氮是最常见的限制植物生长的养分，因此对土地和土壤中的碳储存有重大影响。氮也是一种重要的污染物，这是一个悖论，这取决于它在哪里以及它以什么化学形式存在。氮循环对气候、大气二氧化碳水平和生物多样性同时变化的未来反应是高度不确定的。通过更好地了解氮循环在过去是如何变化的，对未来状况的预测将大大改善。作为该项目的一部分，研究人员将指导一名高中生开展一项以土壤为基础的活动，目标是加利福尼亚州生态科学标准。这项活动将被纳入现有的教育和自然资源管理计划，该计划为来自该州服务不足、少数族裔占主导地位的农业社区的高中生将课堂学习与现实世界联系起来。

The goal of this project is to develop a method to reconstruct how nitrogen cycles of pre-industrial landscapes behaved in the past during periods of environmental and ecological change to enable better insights into potential future changes. Changes in nitrogen dynamics of the past, such as how much nitrogen was available for plants to take up from the soil, or whether losses of nitrogen from ecosystems were greater in water or as a gas to the atmosphere, may be inferred from information contained in the nitrogen isotope ratios of the remains of plant parts that persist in soils. This project will examine the persistence of particular plant compounds in soils and determine if their nitrogen isotope ratios are conserved as the plant residues decompose to form more stable soil organic matter. The need to accurately include the dynamics of nitrogen into models of global carbon and climate is well recognized. Nitrogen is the nutrient which most commonly limits plant growth and, as a result, has a major influence over carbon storage on land and in soils. It is a paradox that nitrogen is also an important pollutant, depending on where it is and what chemical forms it takes. Future responses of the nitrogen cycle to concurrent changes in climate, atmospheric carbon dioxide levels, and biodiversity are highly uncertain. Predictions of future conditions will be greatly improved through greater understanding of how nitrogen cycles have changed in the past. As part of this project, the researchers will mentor a high school student in the development of a soils-based activity targeting the California State Science Standards for ecology. This activity will be incorporated into an existing education and natural resource stewardship program that connects classroom learning to the real world for high school students from underserved, minority-dominated farming communities in the state.