Developing native plants in Eastern United States as Bioindicators of Ambient O3 Exposure
Eight plant species (Black Cherry, White Ash, Yellow-Poplar, Common Milkweed, Black Berry, Dogbane, Big Leaf Aster and Sassafras) were grown in an open top chamber system under full-filtered, half filtered, non-filtered and ambient O3 exposures at the Moshannon State Forest for two growing seasons. Of the eight species tested; Black Cherry proved most sensitive under ambient conditions of O3 exposure; symptoms developed early in the season and became more severe as the season progressed. Symptoms were also negligible in that half filtered chambers and non-exist in the full filtered chambers indicating that this species demonstrates a clear response to elevated ambient ozone exposures.

Common Milkweed and Black Cherry responded similarly to ambient ozone exposures.  It is interesting to note that symptoms developed on Milkweed towards the end of the growing season (exposure) season even within the half-filtered and full-filtered chambers.  This may suggest that Milkweed has a lower overall threshold for season long exposures to ambient ozone.  The ozone exposures of 1996 were considerably lower than several previous years and thus symptoms were much less severe. More severe symptoms would have been noted under higher ozone exposures.  Overall sensitivity ranking would follow as (most sensitive) Black Cherry > Milkweed > Dogbane > Yellow-Poplar > Big Leaf Aster > Blackberry > White Ash > Sassafras; note Sassafras was not fairly tested due to low plant survival following drought in the 1995 season. 

This project was funded by USDA Forest Service and collaborated with Dr. Gretchen Smith, USDA Forest Service, University of Massachusetts, Amherst, MA. 

Diagnosing Ozone Injury
  • Typical upper leaf surface “Stipple”.
  • Stipple does not appear on lower leaf surface.
  • Stipple does not cross over leaf veins.
  • Older leaves will develop earlier and more injury compared to new growth.
  • Ozone exposure and stipple will eventually lead to premature leaf loss.