An empirical model for estimating CO2 exchange of Bouteloua gracilis (H.B.K.) Lag. in the shortgrass prairie.

An empirical model for predicting net photosynthesis (P N ) and dark respiration (R D ) in the field was developed and tested for Bouteloua gracilis (H.B.K.) Lag., the dominant C4 grass of the North American shortgrass prairie. P N is predicted as a function of soil water potential, canopy air temperature, irradiance, and plant age, while R D is expressed as a function of soil water potential and temperature. The model accounted for 85% of the variability in the data base used to estimate parameter values. Results of a validation test showed good agreement between observed and predicted P N rates, suggesting this approach would be useful as a submodel of a grassland ecosystem model.