IMPACT OF OZONE ON MILKWEED (ASCLEPIAS) SPECIES
Open Access
- Author:
- Myers, Abigail C
- Graduate Program:
- Environmental Pollution Control
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 15, 2016
- Committee Members:
- Dennis R Decoteau, Thesis Advisor/Co-Advisor
Donald Durwood Davis, Committee Member
Richard P Marini, Committee Member - Keywords:
- ozone
tropospheric ozone
ground level ozone
bioinidicator
asclepias
injury
air pollution
plant injury
milkweed
asclepias syriaca
asclepias curassavica
asclepias incarnata
asclepias speciosa
asclepias sullivantii
asclepias viridis - Abstract:
- Tropospheric (or ground level) ozone in ambient concentrations can damage vegetation and interfere with the human respiratory system. Plants as bioindicators of ozone are commonly used to detect phytotoxic levels of tropospheric ozone where physical/chemical/electrical monitoring equipment cannot be utilized due to expense, electrical needs, or availability of instruments. Asclepias syriaca (Common Milkweed) has been effectively used as a bioindicator for ozone. Visual ozone injury on Common Milkweed is characterized as purple stippling of the upper surface of older leaves as the season progresses, the purple coloration of the upper leaf surface may encompass most of the leaf surface. While sensitivity to ozone has been documented on Common Milkweed, less is known about the ozone sensitivity of other Asclepias species and little is known regarding the concentration dose response of Common Milkweed to ozone and timing of visual symptoms. Of the Asclepias species evaluated Tropical Milkweed (A. curassavica) had the greatest ozone injury throughout the experiment, suggesting that the species might be a more sensitive bioindicator to ozone than Common Milkweed. However, high levels of leaf loss during the season may negate its usefulness as a bioindicator. Levels of ozone injury on Swamp Milkweed (A. incarnata) were not significantly different from the standard Common Milkweed, and with the exception of the afore mentioned, ozone injury values were typically greater than observed on Common Milkweed. This suggests that ozone injury on Swamp Milkweed develops more quickly or at a greater amount than on Common Milkweed. However, because the injury values were not significantly different, Swamp Milkweed may be a useful ozone-sensitive bioindicator species in the field. The other milkweed species Showy Milkweed (A. speciosa), Prairie Milkweed (A. sullivantii), and Spider Milkweed (A. viridis), developed distinguishable ozone injury symptoms (including dark stippling), and non-significantly different injury ratings from Common Milkweed, suggesting that these species are comparable and may be useful as field bioindicators in addition to or in lieu of Common Milkweed. The amount of injury on Common Milkweed rose at an increasing rate over time and with higher levels of ozone (e.g. 60-90 ppb). Plants exhibited phytotoxic injury at 60 ppb, below the current NAAQS of 70 ppb ozone, which may indicate that the current standard may not be strict enough. Plants exposed to 90 ppb ozone developed injury, although less severe, at the same time as those plants exposed to 90ppb ozone. This result combined with the curvilinear relationship described above indicates that Common Milkweed remains a viable indicator at this level of phytotoxic ozone.