Effects of Ozone or Sulfur Dioxide on Annual Plants of the Mojave Desert

Abstract

Annual plants (47 spp.) from the Mojave Desert were grown in pots and were exposed in open-top field chambers located at Riverside, California to test their relative sensitivity to SO2 and O3. Exposures were 8 h/day, for 4 or 5 days, at 0, 0.05, 0.1, 0.2, 0.3 and 0.4 ppm O3 or 0, 0.2, 0.5, 0.6, 0.8, 1.0 and 1.5 ppm SO2. Species differed widely in their response to the pollutants. Three spp, Camissonia claviformis, Ca. hirtella and Cryptantha nevadensis, were sensitive to both pollutants, exhibiting leaf injury when exposed to 0.1 ppm O3 or 0.2 ppm SO2. Two spp, Festuca octoflora and Lepidium lasiocarpum, were tolerant to both pollutants, exhibiting no leaf injury with concentrations of 0.3 ppm O3 or 1.5 ppm SO2. The other species were intermediate in sensitivity, with O3 sensitivity not always corresponding to SO2 sensitivity. Total S concentration analysis indicated that for 8 of 11 spp. tested, plants exposed to 0.2 ppm SO2 had a higher S concentration than nonexposed plants. Baileya pleniradiata and Perityle emoryi had the greatest increases in S concentration for exposed vs. control plants. To test for effects of the environmental and exposure system on plant sensitivity, 29 spp. exposed in the open-top chambers were grown in the ground and exposed with a modified chamberless zonal air pollution (ZAP) system to SO2 in the Mojave Desert area near Daggett, California. Exposures were for 37 h, over 6 days, to 0, 0.4, 0.8 and 1.0 ppm SO2, with exposures only during periods with due west winds. Most species were not injured with any SO2 exposure concentration used with the ZAP system; only C. claviformis showed injury at 0.8 ppm SO2 and Oenothera californica exhibited injury at 1.0 ppm SO2.