Atmospheric ozone causes formation of various highly reactive intermediates (e.g. peroxyl and superoxide radicals, H202, etc.) in plant tissues. A plant's productivity in environments with ozone may be related to its ability to scavenge the free radicals formed. The effects of ozone on photosynthesis and some free radical scavengers were measured in the fifth emergent leaf of poplars. Clonal poplars (Populus deltoides x Populus cv caudina) were fumigated with 180 parts per billion ozone for 3 hours. Photosynthesis was measured before, during, and after fumigation. During the first 90 minutes of ozone exposure, photosynthetic rates were unaffected but glutathione levels and superoxide dismutase activity increased. After 90 minutes of ozone exposure, photosynthetic rates began to decline while glutathione and superoxide dismutase continued to increase. Total glutathione (reduced plus oxidized) increased in fumigated leaves throughout the exposure period. The ratio of GSH/GSSG also decreased from 12.8 to 1.2 in ozone exposed trees. Superoxide dismutase levels increased twofold in fumigated plants. After 4 hours of ozone exposure, the photosynthetic rate was approximately half that of controls while glutathione levels and superoxide dismutase activity remained above that of the controls. The elevated antioxidant levels were maintained 21 hours after ozone exposure while photosynthetic rates recovered to about 75% of that of controls. Electron transport and NADPH levels remained unaffected by the treatment. Hence, elevated antioxidant metabolism may protect the photosynthetic apparatus during exposure to ozone.All organisms that have evolved in aerobic environments have a variety of enzymatic and nonenzymatic mechanisms to prevent oxidation of cellular components. It is quite probable that existing mechanisms for detoxifying oxyradicals are invoked in response to ozone since it causes the formation of some highly reactive oxyradicals in aqueous solutions, a major product being the superoxide anion (I1). The superoxide anion can be metabolized by several isozymes of superoxide dismutase found in plants (14). The hydrogen peroxide formed by this reaction is toxic. It can inactivate -SH containing enzymes (5, 13) or react with superoxide to form the hydroxyl radical, which can attack many macromolecular

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Much of the information on the effects of air pollutants on plant life has been derived from studies with controlled‐environment, greenhouse, and field fumigation equipment. Each of these is important for the gaining of conditional information on the response of plants to air pollutants, but none of them can simulate ambient environmental conditions. Portable and fixed field fumigation chambers have perhaps come the closest to providing the ambient milieu, but the usual closed design alters normal conditions of light intensity and quality, temperature and humidity fluctuations, precipitation, and free access of insects and plant pathogens.A simple, relatively inexpensive, and light‐weight open‐top chamber of modular design has been built and tested. Each module is 1.22 m (4 feet) high and 2.74 m (9 feet) in diameter, and can be stacked vertically in combinations of 1, 2, or 3 modules. The modules are fabricated from corrugated fiberglass panels attached to aluminum hoops and the air‐delivery plenum from lay‐flat polyethylene tubing. A mobile air filter and blower assembly provides air that has passed through a dust filter and an activated‐charcoal filter. An open plastic mesh placed across the top of the chamber reduces the influence of wind on the air distribution system, but it does not impede the entrance of precipitation or of insects.The chamber was tested in several ways: (i) efficiency of the chamber and filter‐blower assembly for exclusion of ambient oxidants was tested by monitoring the atmosphere and by growing susceptible plants in chambers with or without charcoal filters and in outside plots; (ii) distribution and concentration of an introduced pollutant within the chamber were measured by a dynamic air monitoring method; and (iii) accumulation of an introduced pollutant was studied with both plants and a static monitoring method.

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SUMMARYThe contact angle method was used to determine the wettability of red spruce {Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] foliage in subalpine sites (1010-1400 m above sea level) at three locations in northern New England, USA (Camels Hump in Vermont and Mt. Moosilauke and Mt. Washington in New Hampshire).The dependence of contact angle {()) on foliage age {t, in months) could be expressed in the form 6 = 6, + 6^ e-"'. The value of the decay constant {k) ranged from 0-02 to 0-12 (month"'), depending upon location, but was independent of elevation, canopy position, and, in most cases, species. The asymptotic value of the contact angle ((9j), i.e. that approached by very old foliage, did not differ between species at some sites but was greater in fir than in spruce at others. The value of 6^ decreased with elevation in both species and tended to increase with an increase in height within the canopy. The value of the component which affected contact angle variation with age {6^) was always greater in fir than in spruce, but was unaffected by elevation; in fir, it appeared to increase with height in the canopy. Thus, the estimated value ofthe initial {t = 0) contact angle (0^ + 6.,) was greater in fir, increased with height in the canopy, and decreased with elevation. The overall pattern found was that (1) young foliage of spruce is more wettable than young foliage of fir, but the difference becomes smaller in older age classes; (2) young foliage near the bottom of the canopy is more wettable than near the top; and (3) foliage from a given age class and species is more wettable at higher elevations.The treatment of foliage with xylene to remove epicuticular wax decreased contact angles of fir but increased them in spruce. Scanning electron microscopy revealed that wax removal by xylene did not mimic natural wax removal. Contact angles obtained with acidified water did not vary significantly from those obtained with deionized water.