Will a doubling of atmospheric carbon dioxide concentration lead to an increase or a decrease in water consumption by crops?

Simulations with a soil/vegetation/atmosphere (SVAT) model for normal midlatitude summertime conditions were made for corn and soybeans in order to assess the effect of doubling CO2 concentration on transpiration. A second purpose of this short communication is to emphasize that feedback processes present in the plant canopy but absent in the laboratory can lead to divergence between experimental and simulated results. In contrast with results reported by Cure and Acock (1986), increases in stomatal resistance commensurate with a doubling of CO2 concentration produced negligible changes in simulated transpiration. When we take account of the effect of biomass increases brought about by a CO2 doubling, a small seasonal increase in transpiration is indicated.