HR: 14:25h
AN: B33F-04 INVITED    [Abstracts]
TI: The Role of Nitrogen Dynamics in the Responses of Terrestrial Carbon Dynamics to Changes in Atmospheric Carbon Dioxide, Climate, and Land Use
AU: * McGuire, A D
EM: ffadm@uaf.edu
AF: U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska Fairbanks, Fairbanks, AK 99775, United States
AU: Melillo, J
EM: jmelillo@mbl.edu
AF: Marine Biological Laboratory, The Ecosystems Center, Woods Hole, MA 02543, United States
AU: Kicklighter, D
EM: dkick@mbl.edu
AF: Marine Biological Laboratory, The Ecosystems Center, Woods Hole, MA 02543, United States
AU: Joyce, L
EM: ljoyce@fs.fed.us
AF: USDA Forest Service, Rocky Mountain Research Station, 240 West Prospect, Fort Collins, CO 80526, United States
AB: While it has long been appreciated that alterations of the nitrogen cycle can substantially affect the carbon dynamics of terrestrial ecosystems, most large-scale models of terrestrial carbon dynamics have ignored carbon-nitrogen interactions in making projections of how carbon dynamics will respond to changes in atmospheric carbon dioxide, climate, and land use. Numerous experimental studies have documented that the uptake of carbon by terrestrial ecosystems is enhanced by nitrogen fertilization under baseline and elevated atmospheric carbon dioxide concentrations. Ecosystem warming studies often identify that the uptake of carbon is enhanced when mineralization of soil organic nitrogen increases in response to warming, but the response often depends on how warming affects soil moisture. Nitrogen amendments are a standard practice in heavily managed agro-forestry ecosystems because of the enhanced response of plant growth to nitrogen fertilization. We have used the Terrestrial Ecosystem Model (TEM) as a tool to explore the regional and global implications of how carbon-nitrogen interactions may influence the responses of terrestrial carbon dynamics to environmental change and land use. Comparisons of the model with and without nitrogen dynamics indicate that the response of carbon uptake to increases in atmospheric carbon dioxide are clearly constrained by nitrogen dynamics. In contrast, carbon uptake is enhanced in situations in which warming enhances the mineralization of soil organic nitrogen, and this response can lead to increases in vegetation carbon storage that are greater than losses of carbon from increases in decomposition of soil organic matter. Land use can result in substantial depletion of nitrogen from terrestrial ecosystems in the harvest of agricultural products. As substantial sink activity is associated with forest re-growth after agricultural land abandonment, we conducted simulations with TEM in the eastern United State to evaluate to role of nitrogen replacement in the carbon dynamics of these ecosystems. The comparison of TEM simulations with inventory-based analyses of carbon storage were most consistent for simulations in which soil nitrogen was minimally depleted and in which there was no photosynthetic response to increased atmospheric carbon dioxide. In summary, experimental studies and our analyses with TEM indicate that carbon-nitrogen interactions are important in the regional and global response of carbon dynamics to environmental change and land use. These interactions should be considered by carbon cycle models that are used to assess the responses of terrestrial carbon storage to future environmental change and land use.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0466 Modeling
DE: 0469 Nitrogen cycling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting