Global environmental change caused by anthropogenic emissions is perturbing biogeochemical cycles in terrestrial ecosystems through various ways. A process-based model of carbon and nitrogen cycles in terrestrial ecosystem, VISIT (Vegetation Integrative SImulator for Trace gases), was developed to assess impacts of environmental change on ecosystem patterns and processes. The nitrogen scheme consists of nitrogen pools in mineral soil (NH4+ and NO3-), soil organic matter, microbes, and plant biomass (canopy and storage). It simulates daily nitrogen flows such as mineralization, nitrification, denitrification, leaching, plant uptake, and abandonment, mostly in simplified manner. We focused on N2O emission from soil surface, because it is a major greenhouse gas; thus, VISIT simulating CO2 and CH4 exchange can evaluate net greenhouse gas budget.

Results/Conclusions

The model was applied to East Asian ecosystems: a cool-temperate deciduous broad-leaved forest (Takayanma), a warm-temperate evergreen needle-leaved forest (Fujiyoshida), and boreal deciduous needle-leaved forest (Tomakomai). Nitrogen deposition, which directly exerts impacts on ecosystem nitrogen cycle, was obtained from meso-scale atmospheric model simulation during the period from 1980 to 2003. At each site, the carbon-nitrogen model was calibrated using field data; net carbon budget was validated with flux tower measurement data. N2O emission from forest soils was estimated to be tiny, although nitrogen deposition increased soil inorganic nitrogen. Especiaslly, because Fujiyoshida site is located on volcanic lava with immature soil, N2O emission was almost at the edge of measurement detection. In our forthcoming studies, we apply VISIT to future prediction of ecosystem biogeochemistry at the regional scale, on the basis of appropriate climate and nitrogen deposition scenarios. Also, carbon-nitrogen interactions should be the next target for model analysis.