Predicting Effects of Atmospheric CO 2 Partial Pressure on Forest Photosynthesis

A mechanistic (i.e. hierarchic or explanatory) model of forest canopy mass and energy exchange that has been previously tested with eddy-correlation measurements in the field albeit only at present ambient CO2 partial pressure was used to predict photosynthetic response of a deciduous Quercus-Acer forest in eastern North America to atmospheric CO2 partial pressure. Four partial pressures of CO2 were used in simulations: 28 (pre-industrial), 36 (present), 54 and 72 Pa. This is (one of) the first set(s) of predictions of forest photosynthetic response to CO2 partial pressure made by a mechanistic forest physiology model shown to accurately predict independent field measurements of whole-forest CO2 exchange at the hourly time scale. The model includes a biochemically based Farquhar-type model of leaf mesophyll CO2 assimilation, which is central to its ability to predict photosynthetic response to different CO2 partial pressures. Whole-forest photosynthesis was positively related to CO2 partial pressure, as expected. This was the case under both