Foliar injury symptoms of Saskatoon serviceberry (Amelanchier alnifolia Nutt.) as a biological indicator of ambient sulfur dioxide exposures

Saskatoon serviceberry or Saskatoon (Amelanchier alnifolia Nutt. cv. Smoky) seedlings were planted at five study sites within a 35,000 km2 airshed, that is influenced by a number of isolated stationary sources of sulfur dioxide (SO2), oxides of nitrogen and hydrocarbons, among others. The locations of the five sites were based on the results of a meteorological dry deposition model for the oxides of sulfur and nitrogen. Visible foliar injury responses of Saskatoon were used as a biological indicator of SO2 exposures, through monthly field surveys. During late July 1998, unifacial, interveinal chlorosis was observed on some 12% of the seedlings at one study site. By September, the chlorosis had become more severe (necrosis) on some 70% of the plants at that site. Site specific ambient SO2 levels were relatively low (maximum 5-min concentration of 52.8 ppb). Similar data were unavailable for all, but one other site. Therefore, foliar total S and SO42−-S concentrations were analyzed in September at four of the five study sites. Previously soil SO42−-S at these sites had been analyzed. There were spatial variabilities among these parameters. Based on the overall examination of these data, it is concluded that the observed visible injury symptoms were due to chronic SO2 exposures, exacerbated by the presence of ozone (O3). Independent of this literature based speculation, visible foliar injury responses of Saskatoon can be used as a biological indicator for acute or chronic ambient SO2 exposures, in the presence of other phytotoxic air pollutants.