Systematic review of plant sensitivity to ozone: Application to US National Ambient Air Quality Standards

S. Douglas Kaylor, Center for Public Health and Environmental Assessment, US Environmental Protection Agency, Research Triangle Park, NC and Emmi Felker-Quinn, Air Resources Division, National Park Service, Lakewood, CO

Background/Question/Methods
The Clean Air Act calls for EPA to issue and periodically review National Ambient Air Quality Standards (NAAQS) for tropospheric ozone (O3) and five other air pollutants. Effects of O3 on individual plants range from visible foliar injury and stomatal disfunction to reduction of photosynthesis and plant growth. These effects cascade up to alter populations, communities, and ecosystems. Systematic review (SR), a structured and highly documented process for gathering and synthesizing evidence from existing studies to form conclusions, is a useful scientific tool for informing the NAAQS review. Our SR assesses over sixty years of research to determine what vascular plant species in the US are sensitive to O3, in what ways, and at what exposure levels.
Our systematic review started with a published global-scale literature database of peer-reviewed studies that assessed the effects of controlled O3 exposure on plant species, including reductions in biomass, changes in gas exchange measures, and visible foliar injury. Using citation mapping and literature searches, we added other published references that met these selection criteria. We determined species presence and native/introduced status in the United States using the USDA PLANTS database. Population status (rare, threatened, or endangered) was determined using the IUCN redlist. Cultural and economic importance were assessed using several sources.

Results/Conclusions
Currently, our systematic review includes 710 vascular plant species (which represents 0.1% of vascular plants) evaluated in controlled experiments for O3 sensitivity and published in 295 peer-reviewed studies. Of these, 259 species have populations native to the United States (determined by USDA), and 74.5% of these native species display some O3 sensitivity (growth reduction, foliar injury, yield reduction, or stomatal response). Another 310 species are introduced in the United States, with 83.2% of these exhibiting O3 sensitivity. We will present summaries of our findings regarding the prevalence of certain effects of O3 upon native plant species, the exposure levels at which these effects are observed, effects on different plant growth forms (annuals, perennials and trees) and the possible impact of O3 on specific rare or culturally important species. Additionally, we will present how this work supports the NAAQS review as mandated under the Clean Air Act, informing policy with the best available science.




“The findings and conclusions in this abstract have not been formally disseminated by the U.S. EPA and should not be construed to represent any agency determination or policy.”