HR: 0800h
AN: B31A-0054    [Abstracts]
TI: Effect of a nitrogen-carbon interaction on terrestrial carbon fluxes estimated by biosphere model
AU: * Sasai, T
EM: t.sasai@aist.go.jp
AF: Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology (AIST), Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Yamaguchi, Y
EM: yasushi@nagoya-u.jp
AF: Graduate School of Environmental Studies, Nagoya University, Foru-cho, Chikusa, Nagoya, 464-8602, Japan
AB: It is important for the global warming to accurately understand the terrestrial carbon fluxes at global scale. Estimating spatial and temporal patterns in the carbon fluxes, recently, many global biosphere models were proposed and developed. However, since the model analyses have always some uncertainties. One of the major uncertainties is an effect of nitrogen cycle on the carbon cycle, as nitrogen largely controls carbon dynamics as plant and soil microbe nutrients. A goal of this study is to investigate the effect of terrestrial carbon-nitrogen interaction on NPP using new biosphere model. Firstly, a new nitrogen cycle model was constructed including twelve main nitrogen flows (nitrogen fixation, deposition, nitrifications, volatilization, nitrate leaching, plant uptake, allocation, translocation, retranslocation, soil organic and inorganic nitrogen dynamics), and fourteen pools (three biomass, four litter fall, five soil organic, and two inorganic). Secondly, the nitrogen model was integrated to the existing biosphere model, BEAMS (Biosphere model integrating Eco-physiological And Mechanistic approaches using Satellite data) [Sasai et al., 2005, 2007]. The new biosphere model was run for 20 years (1982-2001) at a global scale. The inputs datasets used were NCEP/NCAR re-analysis and fPAR/LAI based on NOAA/AVHRR produced by Boston University. The two-dimensional distributions of monthly GPP and NPP were calculated. And, the GPP estimates by the original and new BEAMS were compared with ground measurements at flux-tower sites. We compared seasonal changes in GPP between the new model and eddy covariance measurements at flux sites. As a result, the GPP estimates had good agreement with the GPP measurements (r2 = 0.91). In view of a comparison in GPP between the measurements and the original BEAMS (r2 = 0.84), the new model is better than the original BEAMS. Especially, we could observe an indisputable improvement of the new model on a seasonal change in the growing and falling seasons of forest, so that the original BEAMS tends to exaggerate GPP in these stages. In spatial variation in GPP and NPP, a comparison in GPP estimates between the two models was shown that global spatial patterns are roughly much the same, but annual NPP trends are different. Especially, in case of southern Africa and South America, NPP by the original BEAMS showed decreasing trend (-1.8gC/m2/yr), whereas NPP by the new model were turned around (+3.6). We would confirm that nitrogen cycle is largely affected to carbon cycle, and biosphere model need to be developed for gradually increasing the affinity of nitrogen cycle.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0469 Nitrogen cycling
DE: 0480 Remote sensing
SC: Biogeosciences [B]
MN: 2007 Fall Meeting