Micrometeorological determination of time-integrated stomatal ozone fluxes over wheat: a case study in Northern Italy

Ozone deposition fluxes have been measured over a wheat field in Northern Italy in May-June 2001 with the eddy-correlation method in order to evaluate the amount of ozone taken up by plants during the whole grain filling period, from anthesis to harvest. Ozone uptake by plants is due to its penetration through the stomata; for this reason stomata] ozone fluxes were determined, using the analogy with water vapour fluxes (Penman-Monteith approach), which are easily measured. The total ozone dose was obtained by integrating the stomatal ozone fluxes over time. The observational results showed that ozone fluxes decrease with time, following the maturation and the senescence of plants. On the average, the stomatal flux was found to be 50-60% of the total flux, but this fraction decreased during the senescence, emphasizing the importance of non-stomatal ozone deposition pathways. The approach consisting on evaluating the total ozone dose by integrating stomatal fluxes was then compared to the currently used procedure based on the evaluation of the exposure index AOT40, which uses ozone concentrations. Important differences between these two methods are highlighted. The integration of stomatal ozone fluxes appears more suitable for the evaluation of physiological uptake than the use of the exposure index. (C) 2002 Elsevier Science Ltd. All rights reserved.