Emissions Scavenging by Fog, Dew, and Foliage: Foliage Uptake and Consequences for Plants

摘要

Laboratory and field experiments were conducted to test the hypothesis that acidic emissions from space shuttle launches at Vandenberg AFB, or exposure to ambient acid wet deposition, could deplete foliar nutrients in nearby vegetation. The pH of ambient wet deposition in Indianapolis declined in the order dew > rain > fog. Fog was most effective, and dew least effective, in scavenging chemicals from the atmosphere. However, preexisting leaf surface aerosol contamination, and chemical exchanges between leaf tissues and surface moisture, had a substantial effect on rain and dew chemistry following deposition. These effects, which included increased pH and increased or decreased ion concentrations, were most pronounced for dew because it formed as pure water. Exposure to ambient rains and dews did not measurably influence leaf tissue element concentrations. Simulated acid mists were applied to several crop species in the laboratory. All species slightly affected leaf surface droplet acidity. Droplets on pinto bean leaves were enriched in potassium, calcium, and magnesium. Tomatoes were raised hydroponically at three different levels of nutrient availability, under conditions where aerosol deposition was minimal. Efflux or ions into whole-plant leachates was observed and did not change with time during pH 4.0 and 5.6 mistings. At pH 2.5, efflux of several ions increased dramatically over time, and the rate of increase was positively related to foliage element concentrations. Measureable depletion of foliar nutrients occurred only after single exposures to pH 1.0 mists or after several days of repeated misting at pH 2.5. (AW)