Environmental limitations to O-3 uptake - Some key results from young trees growing at elevated CO2 concentrations

Elevated carbon dioxide concentrations and limited water supply have been s hown to reduce the impact of ozone pollution on the growth and physiology o f Quercus petraea in a long-term factorial experiment. These responses can be explained by observed reductions in stomatal conductance, and thus poten tial ozone exposure of 28% and 40% for CO2 and drought treatments respectiv ely. However, parameterisation of a stomatal conductance model for Quercus robur and Fagus sylvatica grown under ambient and elevated CO2 concentratio ns in a separate experiment has demonstrated that elevated CO2 also reduces the responsiveness of stomata to both saturation deficit (LAVPD) and soil moisture deficit (psi) in beech, and to a lesser extent, in oak. Season-lon g model simulations of ozone fluxes suggest that LAVPD and psi conductance parameters derived at ambient CO2 concentrations will lead to these fluxes being underestimated by 24% and 2% for beech and oak respectively at 615 pp m CO2.