REGIONAL APPLICATION OF AN ECOSYSTEM PRODUCTION-MODEL FOR STUDIES OF BIOGEOCHEMISTRY IN BRAZILIAN AMAZONIA

The degree to which primary production, soil carbon, and trace gas flu xes in tropical forests of the Amazon are limited by moisture availabi lity and other environmental factors was examined using an ecosystem m odelling application for the country of Brazil. A regional geographica l information system (GIS) serves as the data source of climate driver s, satellite images, land cover, and soil properties for input to the NASA Ames-CASA (Carnegie-Ames-Stanford Approach) model over a 8-km gri d resolution. Simulation results lead us to hypothesize that net prima ry production (NPP) is limited by cloud interception of solar radiatio n over the humid north-western portion of the region. Peak annual rate s for NPP of nearly 1.4 kg C m(-2) year(-1) are localized in the seaso nally dry eastern Amazon in areas that we assume are primarily deep-ro oted evergreen forest cover. Regional effects of forest conversion on NPP and soil carbon content are indicated in the model results, especi ally in seasonally dry areas. Comparison of model flux predictions alo ng selected eco-climatic transects reveal moisture, soil, and land use controls on gradients of ecosystem production and soil trace gas emis sions (CO2, N2O, and NO). These results are used to formulate a series of research hypotheses for testing in the next phase of regional mode lling, which includes recalibration of the light-use efficiency term i n NASA-CASA using field measurements of NPP, and refinements of vegeta tion index and soil property (texture and potential rooting depth) map s for the region.