Effects of SO2, O3, and SO2 and O3 in combination on photosynthesis and ultrastructure of two lichen species

Abstract

Flavoparmelia caperata (L.) Hale and Umbilicaria mammulata (Ach.) Tuck, were exposed to 262 μg SO₂ m⁻³, 59 μg O₃ m⁻³, and 262 μg SO₂ m⁻³ in combination with 59 μg O₃ m⁻³ for 20 h over a 5-day period. Photosynthesis and ultrastructural observations were made after 12 and 20 h. At these low concentrations of pollutants, ultrastructural changes preceded and accompanied decreases in photosynthesis rates. Ozone was more phytotoxic than SO₂. Ultrastructural damage was least with SO₂ and greater and very similar with O₃ and the combination of O₃ and SO₂. Photosynthetic data showed that SO₂ ameliorates effects of O₃. Electron micrographs showed increased accumulation of starch and cavity space around starch grains in the chloroplast and increased lipids in the cytoplasm in F. caperata; there was some increased starch in U. mammulata, but alterations were primarily in increased chloroplast opacity. Photosynthesis of U. mammulata was more sensitive to the pollutants than that of F. caperata. Ultrastructural damage was greater when samples were stored in the light than when they were stored in the dark between fumigations. The study shows that species vary in their responses to pollutants and that combinations of pollutants may give results different from those obtained with single pollutants.