Model estimates of global carbon flux between vegetation and the atmosphere

The net primary productivity (NPP) of global terrestrial vegetation is esti mated by an Atmosphere-Vegetation Interaction Model (AVIM). AVIM consists o f two intercoupled components: physical processes, involving water and ener gy transfer among soil, vegetation and the atmosphere at the land surface a nd eco-physiological processes, i.e. photosynthesis, respiration, dry matte r allocation, littering, phenology. Globally vegetation is classified into 13 types and soil texture is classified into 6 types. The estimated NPP for different vegetation types at 1637 sites are validated with the observed d ata provided by EMDI. The main results of NPP estimation show that global a veraged NPP is 405.13 g C m(-2)yr(-1), varying from 99.58 g C m(-2)yr(-1) ( tundra) to 996.2 g m(-2)yr(-1) (rainforest). Global total annual NPP is abo ut 60.72Gt C yr(-1), in which the maximum part, about 15.84 Gt C yr(-1), ac counting for 26.09% of the total is contributed by tropical rainforest. The maximum carbon sink occurs in the temperate region of the Northern Hemisph ere. The global spatial and seasonal distribution of terrestrial NPP is est imated reasonably.