HR: 17:45h
AN: B54A-08    [Abstracts]
TI: Sensitivity Analysis of a New Global Coupled Terrestrial Carbon-Nitrogen Model
AU: * Gerber, S
EM: sgerber@princeton.edu
AF: Woodrow Wilson School of Public and International Affairs, Princeton University, Princeton, NJ 08544 United States
AU: * Gerber, S
EM: sgerber@princeton.edu
AF: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544 United States
AU: Hedin, L O
EM: lhedin@princeton.edu
AF: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544 United States
AU: Oppenheimer, M
EM: omichael@princeton.edu
AF: Woodrow Wilson School of Public and International Affairs, Princeton University, Princeton, NJ 08544 United States
AU: Pacala, S W
EM: pacala@princeton.edu
AF: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544 United States
AU: Shevliakova, E
EM: elena@princeton.edu
AF: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544 United States
AB: We add nitrogen dynamics to the existing Geophysical Fluid Dynamic Laboratory land model, LM3V, a dynamic vegetation model that is part of a fully coupled earth system model. The land model includes stoichiometric nitrogen and carbon in living pools, litter and soil organic matter, which, in turn, allow for nitrogen limitation of plant growth and litter decomposition. Plant nitrogen uptake depends on carbon to nitrogen ratios in plant above and belowground tissues, and is constrained by availability of soil mineral nitrogen. A set of litter and soil organic matter pools with characteristic turnover times, allow for enrichment of nitrogen in soil organic matter during decomposition. Net and gross mineralization is explicit, while microbial pools and rates are calculated implicitly based on carbon and nitrogen supply. Nitrogen leaching is a function of water export and soil mineral nitrogen content. We performed an analysis of the model's sensitivity to factors such as climate (temperature and precipitation), nitrogen loading, and episodic disturbances (e.g. fire). The model's transient responses to step changes in forcing variables, or to a simulated catastrophic removal of all the aboveground pools, imply that recovery from perturbation is governed critically by the formation and decay of humic soil organic matter. Incorporation of nitrogen in humic materials with turnover time of decades inhibits the immediate re-use of nitrogen by plants after litter decomposition, and thus offers a key mechanism for maintaining nitrogen limitation during periods of transient reorganization. On the other hand, the slow but steady decay of this decadal pool provides a major source of nitrogen for plant re-growth after a disturbance event that would otherwise be lost from the system in the early period in which plant uptake was weak. Projected climate change alters the nitrogen balance in the model, because increased decomposition rates reduce soil organic matter, thereby mineralizing additional nitrogen. In conclusion, the combination of long time scale with considerable nitrogen throughput in the humic soil organic pool requires a careful evaluation of the parameters for the treatment of soil organic matter in models, and also asks for a better understanding of the biogeochemistry that leads to the formation humic materials.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0469 Nitrogen cycling
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
SC: Biogeosciences [B]
MN: Fall Meeting 2005