ARS | Publication request: EFFECTS OF CO2, N, AND CLIMATE ON ENERGY EXCHANGE OF WHEAT: MODEL TESTING WITH A FACE EXPERIMENT

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 2001
Publication Date: October 21, 2001

Technical Abstract: Changes in mass and energy exchange by crops under rising CO2 may be affected by N and weather. CO2 interacts with weather on latent heat flux (LE) through stomatal conductance, which is affected by CO2, vs. aerodynamic conductance, which is affected by weather. The basis for this interaction was examined with the ecosystem model ecosys. Simulation results were tested with energy flux data from a FACE experiment in which wheat was grown under 548 vs. 363 umol mol-1 CO2 and fertilized with 7 vs. 35 g N m-2. Both model and experimental results indicated that rasing CO2 reduced midday LE by CO2. 50 W m-2 for wheat fertilized with 35 g N m-2, and by CO2. 100 W m-2 for wheat fertilized with only 7 g N m-2. These reductions were smaller under low wind speeds (less than 5 km h-1) and stable boundary conditions when aerodynamic conductance became the dominant constraint to transpiration. At a seasonal time scale, raising CO2 from 363 to 548 umol mol-1 reduced simulated (measured) ET of wheat by 9% (7%) when fertilized with 35 g N m-2, and by 16% (19%) with 7 g N m-2. Changes with CO2 in mass and energy exchange used in climate change studies should therefore reflect the site-specific availability of N, as well as climate attributes such as wind speed.