S. Grossman et al., SIMULATED RESPONSES OF ENERGY AND WATER FLUXES TO AMBIENT ATMOSPHERE AND FREE-AIR CARBON-DIOXIDE ENRICHMENT IN WHEAT, Journal of biogeography, 22(4-5), 1995, pp. 601-609
Increased ambient carbon dioxide has been associated with CO2-induced
stomatal closure which affects growth and evapotranspiration of crop c
anopies. This results in changes of the energy balance components of t
he soil-plant-atmosphere system. The agroecosystem wheat model DEMETER
was linked to a soil-vegetation-atmosphere-transfer module which incl
udes the energy balance of the crop canopy and the energy balance of t
he soil surface. Thus, it was possible to calculate evapotranspiration
, canopy temperature and the changed ratio of sensible and latent heat
fluxes in response to elevated atmospheric CO2 concentrations. The fr
ee-air carbon dioxide enrichment (FACE) technique provided a largely u
ndisturbed regime for atmospheric exchange. During the FACE wheat expe
riment at Maricopa in 1992-93, the effects of elevated atmospheric CO2
concentrations on energy balance and evapotranspiration of the wheat
canopy at about 350-370 mu mol/mol (control) and 550 mu mol/mol (FACE)
were investigated. The recorded data were used for model validation.
Diurnal trends of all energy balance components and the canopy tempera
ture were simulated for FACE and control conditions using hourly weath
er data. Results were compared with the observed data on 16 March 1993
. Simulated cumulative seasonal evapotranspiration was found in good a
ccordance to the observed one. Consistent with observations, the simul
ations suggest that there was a small reduction in evapotranspiration
of about 4%. Of course, with the observed increases in growth, there w
ere even larger increases in water use efficiency.