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Ozone exposure-response relationships parametrized for sixteen tree species with varying sensitivity in the United States
Citation:
Lee, E., C. Andersen, P. Beedlow, D. Tingey, S. Koike, J. Dubois, S. Kaylor, K. Novak, R. Rice, H. Neufeld, AND J. Herrick. Ozone exposure-response relationships parametrized for sixteen tree species with varying sensitivity in the United States. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, , 119191, (2022). https://doi.org/10.1016/j.atmosenv.2022.119191
Impact/Purpose:
Tropospheric ozone (O3) is the ambient air pollutant most detrimental to agricultural and terrestrial forested ecosystems in the Northern Hemisphere. Exposure to ambient O3 levels can decrease stomatal conductance and photosynthetic rates which can lead to reductions in biomass production depending upon tree species. However, how tree species with different anatomical, hydraulic and functional traits respond to O3 in terms of whole plant biomass is unclear. EPA scientists modeled whole plant biomass responses to elevated O3 exposure for 16 North American tree species based on experimental data from outdoor open-top chamber seedling studies conducted by EPA air pollution scientists and their collaborators from 1988 to 1995. PESD scientists developed a reference set of parameters for these seedling exposure-response relationships using a 3-month (92 day) 12-hr W126 O3 metric used by US EPA and other agencies to assess risk to trees from O3 exposure. PESD scientists show that: 1) O3 sensitivity is highly variable ranging from sensitive (black cherry, tulip poplar, ponderosa pine, American sycamore, winged sumac, quaking aspen, and red alder) to intermediate (red maple and sweetgum), and lastly to insensitive (Virginia pine, eastern white pine, chestnut oak, Douglas-fir, table mountain pine, and yellow buckeye); 2) conifers except for ponderosa pine are relatively insensitive compared to broadleaves when exposed to 1.0x and 1.5x ambient O3 concentrations; 3) reductions in total plant biomass typically occur after one year of O3 exposure and, for ponderosa pine, are significantly greater after two seasons of exposure (i.e., cumulative O3 effect); and 4) seedlings respond differentially to O3 exposure by varying the diurnal and seasonal patterns of O3 concentrations. Our work is important for Agency regulatory purposes of evaluating the secondary National Ambient Air Quality Standard for O3 to provide protection for vegetation based on empirical data. Our work supports the use of the 12-h W126 metric in risk assessment and scenario analyses in line with CASAC and EPA recommendations. Our work supports the risk assessment frameworks used by EPA, National Park Service, and other researchers to examine the potential risks of tropospheric O3 to terrestrial ecosystems and the services they provide.
Description:
It is well known that exposure to ambient O3 can decrease growth in many tree species in the United States (US). Our study reports experimental data from outdoor open-top chamber (OTC) studies that quantify total biomass response changes for seedlings of 16 species native to western and eastern North America, which were exposed to several levels of elevated O3 for one or more years. The primary objective of this study is to establish a reference set of parameters for these seedling exposure-response relationships using a 3-month (92 day) 12-hr W126 O3 metric used by US Environmental Protection Agency and other agencies to assess risk to trees from O3 exposure. We classified the 16 species according to their sensitivity, based on the biomass loss response functions to protect from a 5% biomass loss. The three-month 12-h W126 estimated to result in a 5% biomass loss was 2.5-9.2 ppm-h for sensitive species, 20.8-25.2 ppm-h for intermediate species, and > 28.7 ppm-h for insensitive species. The most sensitive tree species include black cherry, ponderosa pine, quaking aspen, red alder, American sycamore, tulip poplar and winged sumac. These species are ecologically important and widespread across US. The effects of O3 on whole-plant biomass depended on exposure duration and dynamics and on the number of successive years of exposure. These species-specific exposure-response relationships will allow US Agencies and other groups to better estimate biomass losses based on ozone exposures in North America and can be used in risk assessment and scenario analyses.
URLs/Downloads:
DOI: Ozone exposure-response relationships parametrized for sixteen tree species with varying sensitivity in the United States