Validity of usual dose-response functions in the case of wheat exposed to free-air fumigation in the Paris region

Abstract

Two wheat varieties (Premio and Soissons) were grown in the field in the Paris region and exposed to moderate levels of ozone through a 50m long linear free-air fumigation device. Plants were ozone-fumigated daily for 56 days (from 12 May to 6 July 2009). O3 exposures at 3 different distances from the fumigation source: 2 m, 3.5 m and 5 m downwind of the source, were compared to control located 15m upwind of the linear source. Hourly average concentrations and cumulative exposure index (AOT40) were calculated. Stomatal conductance measurements and modelling allowed the calculation of the Phytotoxic Ozone Dose (POD06) absorbed by the upper leaves of the canopy. The results show strong correlations between grain yield and both ozone exposure (AOT40 or POD06) indicators. However, there are differences in the dose-response relationship obtained for each variety. Moreover, these relationships are also quite different from the dose-response relationships found in the literature. This can be partly explained by the fact that the use of free-air fumigation systems does not allow to achieve a true control treatment (plants exposed to ozone-free air). The highest production values that could be achieved in an atmosphere without ozone must therefore be extrapolated from experimental data, and this may increase the inaccuracy of calculations of relative yield losses