Benefits of the Phytotoxic Ozone Dose (POD) index in dose-response functions for wheat yield loss

Abstract

A central topic of recent research in ground-level ozone (O3) effects on plants is the shift from exposure based on concentrations to a physiologically more realistic approach based on O3 uptake. Critical test of the evidence for the benefits of the latter approach is of utmost importance for the development of O3 risk assessment. We explored the variability in O3 sensitivity in the wheat response function used for risk assessment by the Convention on Long-Range Transport of Air Pollution (LRTAP). The variation in O3 sensitivity among individual experiments was a factor of six larger when using the concentration-based index AOT40 compared to stomatal O3 uptake based Phytotoxic Ozone Dose (POD). Thus, consideration of environmental variables affecting stomatal conductance, such as solar radiation, air humidity and temperature, explained a substantial part of the variation in O3 response among experiments regardless of cultivar differences. Response-functions based on daytime O3 concentrations for the experiments of the POD response function was compared with the corresponding response function including available global data for O3 effects on field grown wheat yield. On average, there was no difference in O3 sensitivity between the two data sets, although the variation in response was substantially larger for global data. We conclude that POD represents a strong improvement over AOT40. The strength and representativeness of the POD approach highlighted is significant for the development and application of models used for risk assessment of ozone impact on crops.