Stomatal numbers, leaf and canopy conductance and the control of transpiration

De Boer et al. (1) concluded that doubled atmospheric CO2 concentration ([CO2]), by reducing both leaf stomatal density and conductance, would decrease modeled annual transpiration by approximately 60 W m−2 in Florida's subtropical vegetation. This remarkable result was accompanied by statements that current Floridian annual evapotranspiration (ET) is approximately 120 W m−2 and that transpiration is approximately 50% of current ET (i.e., ∼60 W m−2). (The remainder of ET is accounted for by evaporation from soil and interception water.) Because 60 minus 60 W m−2 equals 0 W m−2, modeled transpiration in subtropical Florida would therefore cease with CO2 doubling, implying …