Sulfur dioxide effects on plants exhibiting Crassulacean acid metabolism

Abstract The effects of SO 2 on species exhibiting Crassulacean Acid Metabolism (CAM) were determined with short term-high concentration ‘acute’ greenhouse exposures (0·6 to 3·0 μl liter −1 (ppm) SO 2 for 2 and 8 h), and long term-low concentration ‘chronic’ field exposures (0·35 to 0·90 μl liter −1 SO 2 for 32 to 79 h periodically over 7 to 13 days). In the acute greenhouse exposures, visible injury was observed on Opuntia basilaris Engelm. & Bigel., exposed to 2·0 μl liter −1 SO 2 , but no injury was observed on Ananas comosus (L.) Merr., Bryophyllum blossfeldiana Poelln., Bryophyllum pinnata (Lam.) Pers., or Bryophyllum tubiflora (Harv.) Hamet, exposed to up to 2·8 μl liter −1 SO 2 for 8 h. Stomatal conductance during the exposures averaged 0·067 ± 0·021 mol m −2 s −1 for Opuntia basilaris , 0·029 ± 0·008 mol m −2 s −1 for Ananas comosus , and 0·029 ± 0·008 mol m −2 s −1 for Bryophyllum pinnata. Opuntia basilaris was injured early during the day, but not at night; with the injury appearing as a white necrotic banding across just fully expanded pads. Moderately injured pads would regreen beginning 1 to 2 weeks after exposure. In chronic field exposures, no visible injury from SO 2 was observed on Opuntia basilaris, Dudleya arizonica Rose or Agave deserti Engelm. plants, grown either with supplemental irrigation or natural rainfall. In addition, in the field SO 2 had no effect on CO 2 uptake, total sulfur content, transpiration, or tissue acidity in either the light or the dark, or in irrigated vs natural rainfall plots.