Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2005
Publication Date: 5/1/2006
Citation: Souza, L., Neufeld, H., Chappelka, A.H., Burkey, K.O., Davison, A.W. 2006. Seasonal development of ozone-induced foliar injury on tall milkweed (asclepias exltata) in great smoky mountains national park. Environmental Pollution. 141 (1):175-183. Interpretive Summary: Ozone is an air pollutant that is toxic to plants, causing visible injury to foliage and a reduction in the growth and yield of both crops and natural vegetation. Ground level ozone is formed by the action of sunlight on volatile hydrocarbons and nitrogen oxides produced during fossil fuel combustion. Although frequently considered an urban problem, ozone is actually a regional problem because weather systems transport the pollutants into agricultural areas and forests. One approach to assess and compare ozone effects on vegetation in different locations is to identify ozone-sensitive plants that can be used as bio-indicators. Tall milkweed, an understory, perennial wildflower, is known to be extremely sensitive to tropospheric ozone. In this study, tall milkweed populations in Great Smoky Mountains National Park were assessed throughout the growing season in 2000 and 2001. Ozone-sensitive and insensitive individuals were identified based on leaf injury symptoms. A key finding was that ozone causes premature leaf loss that is not accompanied by foliar injury symptoms in sensitive plants, suggesting that foliar injury assessments may underestimate ozone impacts.
Technical Abstract: The goals of this study were to document the development of ozone-induced foliar injury, on a leaf-by-leaf basis, and to develop ozone exposure relationships for cohorts of leaves and individual tall milkweeds (Asclepias exaltata L.) in Great Smoky Mountains National Park. Plants were classified as either sensitive or insensitive based on the amount of foliar injury. Older leaf cohorts were more likely to belong to high injury classes by the end of each of two growing seasons. In addition, leaf loss was more likely for older cohorts (2000) and lower leaf positions (2001) than younger cohorts and upper leaves, respectively. Most leaves abscised without prior ozone-like stippling or chlorosis. Failure to take this into account can result in underestimation of the effects of ozone on these plants.