On the response of two populations of Quercus coccifera to ozone and its relationship with ozone uptake

Ozone (O3) effects on the growth and gas exchange-related parameters of two ecotypes of Quercus coccifera L. presenting different traits in the field were assessed during a 2-years exposure experiment. One-year-old seedlings grown from the acorns collected at a rock (rock ecotype) or at a well-developed soil (garrigue ecotype) were continuously exposed in open-top chambers to three different O3 treatments: charcoal filtered air, non-filtered air and non-filtered air supplemented with 40 nl l−1. Above-ground relative growth rate (RGR) and gas-exchange-related parameters were measured during each growth season. Above- and below-ground biomass were also measured at the beginning and the end of the experiment. Ozone exposure did not induce any significant effect on RGR or any biomass-related parameters. However, the two populations differed in their sensitivity to O3 regarding gas-exchange-related parameters. The observed responses were related with accumulated O3 exposure or cumulative O3 uptake. Although the re-parameterisation of the existing European Monitoring and Evaluation Programme O3 uptake model improved its performance by 30%, O3 accumulated exposure was a better predictor of the observed responses than O3 uptake. The results of the present experiment indicate the need of taking into account the intraspecific variations in plant sensitivity to O3 when assessing the potential risks or impacts of this pollutant.