The proposed research on the influence of leaf surface wetness on photosynthetic CO2 exchange and transpirational water loss will provide a ground-breaking study of a widespread phenomenon in nature. Because a water-film will curtail CO2 uptake dramatically, terrestrial plants must repel water from leaf surfaces. This is despite the frequent occurrence of natural leaf wetting events such as rain, dewfall, ground fog, cloudmist and spray deposition. Preliminary evidence suggests that leaves of numerous species have evolved extreme water- repelling characteristics to prevent stomatal pores from being covered with a water film. This water-repelling capability appears to have co-evolved with structural and orientation features that interact to strongly influence water retention. In some cases, a high water repellency in the form of water bead formation coincides with a high retention. This combination may result in water use efficiencies much higher than previously reported, as will as enhanced CO2 uptake due to higher humidity and, thus, greater stomatal opening. The above results for native plant species may also have substantial applied significance for production in agricultural species. For example, the common practice of spray irrigation during midday to prevent stomatal closure may only be effective for species with non-wettable leaf surfaces. The specific effects of spray-type irrigation on CO2 uptake and yields has not been investigated for crop species. A more fundamental understanding of leaf wetness effects on CO2 exchange in native plants, and corresponding adaptations could lead to a more strategic system of matching irrigation systems to species- specific traits for leaf water-repellency, or artificial selection for certain leaf traits that could enhance water use efficiency as well as carbon gain. **//
