ENVIRONMENTAL-CONTROL OF OZONE UPTAKE IN LARIX-DECIDUA MILL - A COMPARISON BETWEEN DIFFERENT ALTITUDES

We studied ozone (O-3) uptake by European larch (Larix decidua Mill.) needles under ambient conditions at both a low and a high elevation si te. At a given ambient O-3 concentration, the rate of O-3 uptake by ne edles was effectively controlled by stomatal conductance and, hence, b y factors such as light, humidity and water status, which control stom atal conductance. At both study sites, atmospheric water vapor pressur e deficit (VPD) was the climatic factor most closely correlated with a mbient O-3 concentration. Thus, when ambient O-3 concentrations were h ighest, O-3 flux into the needles tended to be restricted by narrowing of the stomata. Mitigation of potential O-3 stress by stomatal closur e was most marked at the low elevation site where both soil water stre ss and atmospheric VPD were greater than at the high elevation site.