| Ambient (O3) ozone concentrations were compared to ozone damage on milkweed plants to determine if there was a correlation. Eight survey sites of at least 100 plants each were located within 5 kilometers of Air Quality Index (AQI) stations in southern Ontario. Sites were visited nine times from June-September (2007) and milkweed leaves from 75 plants were assessed using methods pioneered in the United States. Ambient O3 results were calculated into SUM65, seasonal cumulative O3, and total O 3. The O3 exposure indices SUM65 and cumulative O3 were tested statistically to determine which index is biologically relevant to milkweed as an O3 damage indicator species. The milkweed damage indices were incidence of leaves damaged per plant, incidence of plants damaged per site, and total O3. The incidence of plants injured per site was the best damage parameter with an F(1,28)=17.37, p=0.0003 for SUM65 and F(1,28)=7.5, p=0.0106 for cumulative O 3. Milkweed plants showed quantifiable ozone damage with minimal spatial differences in damage and thus have potential use as a biomonitor species in southern Ontario. |
