OZONE UPTAKE IN THE SUN AND SHADE CROWN OF SPRUCE - QUANTIFYING THE PHYSIOLOGICAL-EFFECTS OF OZONE EXPOSURE

The uptake of air pollutants depends both on pollutant concentration a nd on stomatal conductance. This paper deals with the uptake of ozone (O3) from the air into the needles of Norway spruce [Picea abies (L.) Karst.] under ambient climatic conditions. Regulation Of O3 uptake by the stomata is shown and also the difference between the ''physiologic ally active O3 concentration'' and the O3 concentration of the ambient air. Data from the sun and shade crown of spruce trees at 1000 m a.s. l. are presented. Analysis of data from three vegetation periods has s hown that at low ambient O3 concentrations the O3 uptake is largely re gulated by stomatal conductance. Water vapour pressure deficit (VPD) o f the atmosphere is the climatic factor which showed the highest posit ive correlation with O3 concentration. However, a high leaf-air VDP le d to stomatal closure, thus reducing the O3 uptake in the needles desp ite high O3 concentrations in the ambient air. The potential O3 stress caused by high O3 concentrations can be strongly mitigated by this na tural closing of the stomata and the simultaneous occurrence of modera te drought stress.