SIMULATION OF ELEVATED CO2 EFFECTS ON DAILY NET CANOPY CARBON ASSIMILATION AND CROP YIELD

Three formulations for estimating the impact of elevated CO2 on daily net canopy carbon assimilation (A) are compared. The formulations are all physiologically based but vary in the detail with which A is repre sented. When implemented in two crop models, all formulations predict increased yield under elevated CO2, with the formulation incorporating the most detailed representation of A predicting the smallest yield i ncrease. In the crop model with more complex representations of growth and yield, and where increased photoassimilates under elevated CO2 ar e allowed to affect processes such as leaf area development, yield pre dictions under elevated CO2 can be substantially greater than the pred icted increase in A for each formulation. These results indicate that the representation of A and assumptions regarding adaptation to elevat ed CO2 of A, crop growth and carbon partitioning will have large impac ts on simulation model predictions of crop yields at elevated CO2. (C) 1998 Elsevier Science Ltd. All rights reserved.