Long-Term Symptoms Due to Metal and Acid Precipitation Treatments in Scots Pine (Pinus sylvestris) Needles in the Subarctic

AbstractIn naturally harsh environments, such as arctic-alpine regions, even low levels of anthropogenic pollution appear to have detrimental impacts on plants. We studied the symptoms induced by metal and acid rain treatments in the ultrastructure of Scots pine (Pinus sylvestris) needles in one of the northernmost pine stands in the world at the Kevo Subarctic Research Station, Finland. Adult Scots pines at their natural growing site were irrigated during 1991–1996 with (1) water, (2) acid (pH 3), (3) copper and nickel (below CuNi), (4) Cu and Ni combined with acid, or (5) left unirrigated. The two youngest needle age classes were sampled in September 1996 for microscopy and elemental analyses, and the three youngest needle age classes for an evaluation of visible injuries. The CuNi treatment increased significantly both Ni and Cu concentrations. The accumulation of Cu in C + 1 needles was enhanced by acid addition. CuNi addition did not increase visible injuries, but significantly more ultrastructural dark accumulations and swollen thylakoids were seen in CuNi-treated C + 1 needles. The results show that, even in a seemingly harsh environment, pines are able to resist acid and metal-induced stress for a few years. However, tree growth is likely to suffer in the long run because the injuries seen in older needles suggest that the total capacity of the photosynthetic machinery is likely to decrease.