Nitrogen Constraints On Terrestrial Carbon Sequestration, From Trees To The Globe
| dc.contributor.author | Thomas, Robert | en_US |
| dc.contributor.chair | Goodale, Christine L | en_US |
| dc.contributor.committeeMember | Fahey, Timothy James | en_US |
| dc.contributor.committeeMember | Mahowald, Natalie M | en_US |
| dc.date.accessioned | 2013-09-05T15:26:26Z | |
| dc.date.available | 2018-01-29T07:00:36Z | |
| dc.date.issued | 2013-01-28 | en_US |
| dc.description.abstract | Nitrogen (N) is an essential nutrient for plant growth that constrains the fixation and storage of carbon (C) in many ecosystems. Understanding how environmental change, especially increasing N deposition, carbon dioxide concentrations, and soil temperature, alters the N limitation of forest growth is critical for accurately predicting future C storage and climate change. Accurate predictions depend on developing a historical and present day evaluation of N controls on C storage and using this knowledge to assess and improve global models. In this dissertation, I first demonstrate that N deposition has increased C storage in trees during the 1980s and 1990s across the northeastern U.S. Second, I show how integrating four different observational and experimental datasets (N fertilization experiments, N deposition gradients, 15N tracer studies, and small catchment N budgets) provide unique insights for testing and improving Earth System models. By comparing model output to globally-distributed N fertilization experiments, I demonstrate that two prominent Earth System models (the CLM-CN and O-CN) differ widely in their sensitivity to step increases in N fertilization. Third, a separate analysis focused on the CLM-CN found that the model was not sensitive enough to N deposition in comparison to historical N deposition data. By comparing CLM-CN output to both 15N tracer studies and small catchment N budgets, I show that the low response to N deposition is partially due to low ecosystem retention of N. Model improvements to the CLM-CN that decreased photosynthesis and introduced a more closed N cycle (i.e., lower N inputs relative to internal cycling) increased ecosystem retention of N, decreased the productivity response to N fertilization, and increased the productivity response to N deposition, thereby yielding much more similar model predictions to observations. Overall, this dissertation increases our knowledge of how N deposition influences C storage and is the first to explicitly benchmark C and N interactions in Earth System models using a range of observations. In addition, my work sets a foundation for estimating the impact of N cycling on climate and creates a framework for future evaluations of Earth System models. | en_US |
| dc.identifier.other | bibid: 8267601 | |
| dc.identifier.uri | https://hdl.handle.net/1813/33925 | |
| dc.language.iso | en_US | en_US |
| dc.subject | Forest carbon and nitrogen cycles | en_US |
| dc.subject | nitrogen deposition | en_US |
| dc.subject | ecosystem and Earth System modeling | en_US |
| dc.title | Nitrogen Constraints On Terrestrial Carbon Sequestration, From Trees To The Globe | en_US |
| dc.type | dissertation or thesis | en_US |
| thesis.degree.discipline | Ecology | |
| thesis.degree.grantor | Cornell University | en_US |
| thesis.degree.level | Doctor of Philosophy | |
| thesis.degree.name | Ph. D., Ecology |
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