| MAESTRA2, a species specific mechanistic model, was parameterized to estimate water use, carbon accumulation and organ specific respiration of five deciduous tree species under both irrigated and water stressed conditions. The model was validated using temporally and spatially explicit ecophysiological data to account for seasonal changes in species physiology. The following tree species: Acer rubrum L. 'Summer Red' (A. rubrum ), Betula nigra (B. nigra), Paulownia elongata (P. elongata), Quercus nuttallii (Q. nuttallii), and Quercus phellos (Q. phellos) were intensively measured and organ specific destructively harvested samples were compared to modeled estimates of carbon accumulation. Among species, we observed variability in carbon dioxide exchange rates under well watered and water stressed conditions. A. rubrum carbon sequestration under water deficit was 29% less than the well watered treatment. The species other than A. rubrum were similar to each other (56%-63% less carbon sequestered as compared to the well watered). A. rubrum root biomass was higher in the drought treatment as compared to the well watered control, possibly explaining its carbon sequestration characteristics. Modeling validation results indicated that the model does have the capability to down regulate photosynthetic capacity on a per species basis. Differences between measured values and modeled estimates were within 6% for A. rubrum, 12% for B. nigra, 8% for P. elongata, 2% for Q. nuttallii, and 7% for Q. phellos. Therefore, seasonal carbon accumulation estimates adequately represented field observations in both well watered and drought treatments. Moreover, sap flux measurements confirmed the models ability to estimate diurnal gas exchange under both well watered and water stressed conditions. The work provides evidence that MAESTRA2 is a process-based model capable of accurately quantifying spatially explicit carbon dioxide exchange rates at the species level and in response to water stress. |
