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

Surface deposition is an important sink that removes ozone from pollut ed air basins, and leads to crop damage and ecosystem decline. Physiol ogical and physical processes controlling deposition to vegetated surf aces are incompletely understood. We investigate the relationship betw een ozone flux to trellised grape, F, and canopy stomatal conductance to ozone, g(c), under dew-wetted and dry conditions. Empirically measu red stomatal conductance was scaled to g(c) using empirical measuremen ts 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). Surfa ce wetness substantially increased V-d and g(surf). Under all conditio ns, g(c) < g(surf), suggesting a significant non-stomatal (residual) p athway for ozone deposition, g(r). This residual term, g(r), was incre ased 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(su rf) were dominated by g(c), which may be used effectively to predict o zone deposition to physiologically active vegetated surfaces. Dew form ation enhanced ozone deposition to the hypostomatous leaves of this gr ape canopy by a nonstomatal pathway.