Cellular injuries in epiphytic lichens transplanted to air polluted areas

Abstract

The epiphytic lichens Hypogymnia physodes (L.) W. Wats, and Bryoria capillaris (Ach.) Brodo & D. Hawksw. growing on spruce branches were transplanted from a clean rural area to the environment of a fertilizer plant and a pulp mill in central Finland. The common major pollutants in these environments are SO2, NOx and ammonia but the fertilizer plant also emits fluorides. In the transmission electron microscope two main types of cellular injuries were observed both in algal and fungal cells in both species and in both environments. The first type, characterized by rapid degeneration of cell organelles, was an apparently acute injury leading to plasmolysis and rapid death of the cells. The second type was considered chronic injury and involved changes in chloroplast shape, swelling of mitochondria and increased density of cytoplasm in algal cells, and increased vacuolization and appearance of dark vacuolar accumulations in fungal cells. The cytoplasmic storage droplets decreased gradually in size both in algae and fungi. The acute injury was mainly seen in the lichens transplanted to sites with higher pollution levels near the sources, and was more usual in algal than in fungal cells. B. capillaris was more susceptible to acute injury than H. physodes. An additional injury type was detected in algal cells of both lichen species in the vicinity of the fertilizer plant. This type was characterized by severe swelling of thylakoids and their interspaces and granulation of thylakoid membranes, and was suspected to be related to the effects of fluorides. The injuries as seen in light microscope, and expressed as increased proportion of dead algae and visible bleaching of thallus, were usually observable simultaneously. The injuries as seen in the electron microscope always preceded other injuries; they were clearly observable already after one week of transplantation in the more polluted sites but developed more slowly in the less polluted ones. The time lack between these injuries and the visible ones was 2–3 weeks in the more polluted sites, but several months or even years in the less polluted ones.