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

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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.