Synthesis studies from old-growth tropical forest plot networks indicate a net pantropical carbon sink of more than 1 Pg C/yr, or ~15% of total anthropogenic CO2 emissions. However a number of confounding factors limit our ability to attribute these changes to direct CO2 fertilization of tree growth and forest productivity. Of primary importance is determining if the plots adequately sample natural disturbance and recovery gradients, and the larger landscape successional mosaic. In addition, forest biomass dynamics which include tree growth, recruitment and mortality can interact in complex ways with changes in forest productivity and carbon accumulation. Much can also be gained from studying how tropical forest trees currently metabolize carbon in response to changes in resource supply. This talk will cover these carbon cycle topics in an integrative way, covering 20 years of research in Amazon forests.