Partitioning of ozone deposition over a developed maize crop between stomatal and non-stomatal uptakes, using eddy-covariance flux measurements and modelling E. Lamaud a, *, B. Loubet b , M. Irvine a , P. Stella a , E. Personne c , P. Cellier b a Ephyse, INRA, Villenave d’Ornon, France b Environnement et Grandes Cultures, INRA, Thiverval-Grignon, France c Environnement et Grandes Cultures, AgroParisTech, Paris, France 1. Introduction Tropospheric ozone (O 3 ) is known to damage vegetation, affecting stomatal functioning and several other physiological functions (Fowler, 1992; Lefohn, 1992). To evaluate the impact of O 3 on vegetation, it is not enough to know the ambient concentration to which the plants are exposed, but it is also necessary to determine the amount that is actually absorbed by the plants via their stomatal activity (Fowler et al., 2001; Gerosa et al., 2003, 2004, 2005; Cieslik, 2004). Surface flux of O 3 is also an important variable in air-quality models and must be determined accurately in order to predict the ambient ozone concentration. It is therefore of primary importance to be able to discriminate the rate and amount of ozone which deposits on a vegetal canopy through the various possible pathways: stomatal uptake, cuticular uptake, deposition at the soil surface, or destruction by chemical reactions. To establish the effective exposure of plants to ozone, not all pathways necessarily need to be known. By combining O 3 concentration measurements and estimations of the stomatal conductance, one has obtained knowledge of the dose absorbed by the plants. However, the determination of the O 3 stomatal conductance is not trivial. Whatever the method used, the values are subject to uncertainties. Therefore, a model for the overall ozone canopy conductance, that includes all pathways, is also Agricultural and Forest Meteorology 149 (2009) 1385–1396 ARTICLE INFO Article history: Received 22 June 2008 Received in revised form 15 March 2009 Accepted 19 March 2009 Keywords: Ozone Stomatal and non-stomatal uptakes Soil cuticular and in-canopy aerodynamic resistances Humidity Nitrogen monoxide ABSTRACT Ozone (O 3 ) flux measurements, obtained by eddy-covariance technique, over a developed maize crop were used to partition the overall O 3 deposition between stomatal and non-stomatal uptakes. Data were analysed using a big-leaf model, which was developed from current knowledge on O 3 deposition. The classical parameters used in dry deposition models (i.e. the in-canopy aerodynamic resistance R ac , the intrinsic ground resistance R ig and the cuticular resistance R cut ) were determined for the maize crop from the relationship between the experimental non-stomatal conductance (g ns ) and the friction velocity (u * ) in dry conditions (relative humidity (RH) < 60%). g ns was determined as the difference between the O 3 canopy conductance (g c ) and the O 3 stomatal conductance (g s ), where g s was estimated by a method which combines the Penman–Monteith approach and the use of the CO 2 assimilation flux. Data analysis revealed that chemical reactions between O 3 and nitrogen monoxide (NO) between the canopy top and the O 3 flux measurement level (z m ) could induce high values of the observed O 3 conductance, not representative of ozone deposition to the canopy. The actual O 3 canopy conductance was derived from the observed O 3 conductance by including a correction term function of z m and the NO concentration at this height, based on the previous studies on O 3 destruction above canopies. The estimations of R ac , R ig and R cut given by the non-linear regression of g ns vs u * are in agreement with previously published results. Our analysis also confirms previous studies which have shown that the cuticular conductance (g cut ) increases exponentially with RH, and we propose a new parameterization of g cut as a function of RH, based on experimental evidence. Using our model to partition the total O 3 deposition to the canopy, we showed that the relative contributions of stomatal and non-stomatal uptakes varied strongly with the physiological activity of the maize and the meteorological conditions. This point is of major importance for studies dedicated to the impact of ozone on plant physiology, since it emphasizes the necessity to determine accurately the amount of O 3 actually absorbed by the plants via their stomatal activity. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +33 5 57 12 24 14; fax: +33 5 57 12 24 20. E-mail address: lamaud@bordeaux.inra.fr (E. Lamaud). Contents lists available at ScienceDirect Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet 0168-1923/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agrformet.2009.03.017