Effects of ozone and sulfur dioxide on four epiphytic bromeliads

Plants of Tillandsia balbisiana, T. paucifolia, T. recurvata and T. utriculata exposed to 0.15, 0.30 or 0.45 ppm O 3 or to 0.30, 0.60 or 1.20 ppm SO 2 for 6 hr or sequentially to 0.30 ppm O 3 (2 hr), 0.30 ppm O 3 plus 0.60 ppm SO 2 (2 hr) and 0.60 ppm SO 2 (2 hr) did not exhibit visible injury. Fumigations also had no effect on foliar conductance or on ΔH + associated with Crassulacean acid metabolism. Characteristics responsible for plant tolerance to short exposures to these two gases probably included low stomatal conductance, the insulating indumentum of absorbing foliar hairs and inherently slow metabolism. Reasons for postulating that Tillandsia is a better indicator for technological metals and certain other pollutants than for brief exposures to O 3 and SO 2 are discussed. We also conclude that epiphytic Tillandsia spp. offer advantages over lichens for air quality assessments under appropriate conditions. As vascular plants they exhibit sensitive, easily measured responses to stress and can be transplanted with ease to areas where neither they nor lichens occur naturally.