EFFECTS OF STOMATAL CONDUCTANCE AND SURFACE WETNESS ON OZONE DEPOSITION IN FIELD-GROWN

Surface deposition is an important sink that removes ozone from polluted air basins, and leads to crop damage and ecosystem decline. Physiological and physical processes controlling deposition to vegetated surfaces are incompletely understood. We investigate the relationship between ozone flux to trellised grape, F, and canopy stomatal conductance to ozone, g(c), under dew-wetted and dry conditions. Empirically measured stomatal conductance was scaled to g(c) using empirical measurements of leaf area index, L, single leaf stomatal response to photon flux density, I, and bulk canopy radiation extinction coefficient, K. Leaf wetness was determined with surrogate leaves covered with electrical impedance grids. Deposition velocity, V-d, and surface conductance, g(surf), were positively and highly significantly related to g(c). Surface wetness substantially increased V-d and g(surf). Under all conditions, g(c) < g(surf), suggesting a significant non-stomatal (residual) pathway for ozone deposition, g(r). This residual term, g(r), was increased under wet conditions by a constant amount over the full range of g(c). Expected errors of +/- 20% in the single leaf model, in L, or in K, did not influence these conclusions. We conclude that V-d and g(surf) were dominated by g(c), which may be used effectively to predict ozone deposition to physiologically active vegetated surfaces. Dew formation enhanced ozone deposition to the hypostomatous leaves of this grape canopy by a nonstomatal pathway.