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 SO 2 m −3 , 59 μg O 3 m −3 , and 262 μg SO 2 m −3 in combination with 59 μg O 3 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 SO 2 . Ultrastructural damage was least with SO 2 and greater and very similar with O 3 and the combination of O 3 and SO 2 . Photosynthetic data showed that SO 2 ameliorates effects of O 3 . 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.