EFFECTS OF OZONE AND SULFUR-DIOXIDE ON 2 EPIPHYTIC ORCHIDS

Plants of Encyclia tampensis (Epidendrum tampense) and Epidendrum rigidum (Orchidazeae) exposed to 0.3, 0.6 and 1.2 ppm SO2 or 0.15, 0.3 and 0.45 ppm O3 for 6 hr as well as sequentially to 0.3 ppm O3 (2 hr), 0.3 ppm O3 plus 0.06 ppm SO2 (2 hr) did not exhibit visible injuries. Exposures to pollutants were also without effect on stomatal conductance and Crassulacean acid metabolism (CAM, i.e. carbon fixation at night). The leaf resistance of the two orchids to these gases may be due to structural factors as well as to the generally lower sensitivity of CAM plants to pollutants. © 1990.