NE1013: Mechanisms of Plant Responses to Ozone in the Northeastern US
Statement of Issues and Justification
Surface level (tropospheric) ozone (O3) is all-pervasive and is considered to be the most important phytotoxic air pollutant across many parts of the US and rest of the world (Krupa et al. 2001). This O3 is also a "greenhouse or atmosphere warming gas", a component in the observed and/or predicted global climate change. Despite the national air quality regulations aimed at controlling surface level O3 pollution, it continues to be of major concern for crop production and forest health in the northeastern US and elsewhere (US EPA 1996). In the northeast, during 1996-2001, there were as many as 8 yearly violations of the US EPA's one-hour National Ambient Air Quality standard for O3 of 120 ppb. Although that standard has been revised to an average 8-hour 80 ppb value, the one-hour standard is still in place for monitoring non-attainment areas. In the application of the one-hour standard, based on the influence of meteorology in the production of O3, the second daily maximum hourly O3 value is used as an indicator of air quality attainment versus non-attainment and in examining the multi-year trends. The range of second maximum hourly concentrations in Pennsylvania, Massachusetts, New Jersey, New York and Maryland were respectively 78-129, 78-136, 80-137, 81-139 and 107-144 ppb. California long considered to be the area in the US with the most smog (includes O3) problems, exhibited a second highest maximum of 74-144 ppb, with a minimum value lower than Maryland (74 versus 107 ppb). Thus, the northeast clearly represents a geographic region of concern regarding O3 pollution. In comparison, the ranges of second maximum hourly values in the other participating states, Oregon, Virginia, Alabama, North Carolina and Minnesota were 70-136, 93-130, 84-118, 87-114 and 74-93 ppb (http://oaspub.epa.gov/airsdata/adaqs.trends?geo=01&cnty=&geoin).Ozone sensitive crops in the northeast and in other participating states include: alfalfa (Medicago sativa), bean (Phaseolus vulgaris), corn (Zea mays), cotton (Gossypium hirsutum and G. barbadense), grape (Vitis vinifera), potato (Solanum tuberosum), soybean (Glycine max), tobacco (Nicotiana tabacum), wheat (Triticum aestivum) and melon (e.g., Cucumis melo and Citrullus lanata). Among the 80 major tree species in the eastern US, black cherry (Prunus serotina), eastern white pine (Pinus strobus), green ash (Fraxinus pennsylvanica), sassafras (Sassafras albidum), sweetgum (Liquidambar styraciflua), quaking aspen (Populus tremuloides), willow (Salix spp.) and yellow or tulip poplar (Liriodendron tulipifera), are all known to be O3 sensitive (Krupa et al. 1998). In addition to causing visible foliar injury on sensitive plant species as reported from some 38 countries across the world, chronic exposures to O3 can result in reductions in crop yield and quality and in forest growth and productivity (Krupa et al. 2001). For example, ambient O3 exposures in Long Island, New York, in North Carolina and in California can be high enough to cause respectively a 25%, 39% and >50% biomass reduction in sensitive versus tolerant clones of white clover (Trifolium repens) (McGrath 2000; Heagle et al. 1995). Similarly, on Long Island, New York, a 21% yield reduction was observed in sensitive versus tolerant cultivars of snap bean (Phaseolus vulgaris) (McGrath 2000). Nutritive quality of bahiagrass (Paspalum notatum) and sericea lespedeza (Lespedeza cuneata) was decreased by 6% and 7%, respectively, as a result of chronic exposure to O3 (Powell et al. 1999; Muntifering et al. 2000). Independent of these limited efforts, there is need for a much broader conduct of these types of studies to assess O3 impacts at the regional (e.g., NE) and national level to validate crop loss estimates. During 1996, the US EPA estimated that O3 alone causes > $1 billion in crop loss annually.
Similar estimates are not available at the present time for forests and native vegetation, although the adverse effects of O3 on our national parks and forests are evident (McLaughlin and Percy 1999). For example, in Acadia National Park in Maine, black cherry, quaking aspen, white ash (Fraxinus americana), jack pine (Pinus banksiana), big-leaf aster (Aster macrophyllus) and spreading dogbane (Apocynum androsaemifolium) are sensitive, exhibiting foliar injury (Kohut et al. 1997). Similarly, widespread O3-induced foliar injury was observed on the native black cherry and tall milkweed (Asclepias exaltata) in the Great Smoky Mountains National Park (Chappelka et al. 1997, 1999). Foliar injury on black cherry was also widespread in Pennsylvania and many other eastern states (Skelly et al. 1997).
An intriguing aspect of O3 is its mechanism of action. Ozone is highly reactive, unstable and does not accumulate in plant tissue. Ozone is an oxidant, thus it can serve as an excellent model in understanding the mechanisms of action of oxidative stress caused among others, by biotic pathogens, herbicides such as paraquat, drought and increased ultraviolet (UV)-B radiation (part of global climate change) (Sandermann 1996). It is important to note that oxidative stress also occurs in humans.
Based on the current state of our knowledge, there are many issues that clearly require significant attention. They include, (1) spatial and temporal distribution of O3-induced adverse effects on growth and productivity of crops and forests in the northeast and elsewhere in the US; (2) comparison of those results to other temperate regions such as Canada and the European countries; (3) mechanisms of O3 toxicity and tolerance in plants; (4) interactive effects of O3 with other growth regulating factors such as increases in carbon dioxide or changes in climatic factors (climate change) and incidence of pathogens and pests; (5) scaling the patterns of seedling responses to mature trees and forests; (6) effects of O3 in altering biological diversity and plant community structure within the context of climate change and (7) establishing biologically meaningful numerical relationships between ambient O3 and adverse plant responses.
No single institution can fulfill the stated needs nor function in isolation, because many of the components from molecular to whole plant responses are inter-related. Addressing these issues has direct relevance to air quality regulatory policies and protection of the food supply and natural resources. Target audiences include, the US EPA, US National Park Service and USDA Forest Service, crop growers, members of the horticulture and forest production/management sectors, urban planners and industries contributing to the air emissions of O3 precursors. At the local level, audiences include: home and Master Gardeners, landscape and nursery managers, arborists and managers of public parks and recreational lands and individual crop producers. However, the underlying effort requires multi-disciplinary input and collaboration. With regard to the effects of O3 on plants, the NE-176 Multi-state Project represents the single largest cooperative work among the academic institutions and their scientists in the northeast and the US. In addition to experiment stations, program scientists include those from governmental agencies in the US and in Canada. Other linkages include scientists from the Commission of the European Communities (CEC) that have similar collaborative research programs. Regarding O3, NE-176 scientists (members of academic institutions, USDA-ARS, USDA Forest Service, etc.) bring together a unique diversity of expertise and interests that vary from molecular biology to plant physiology to field studies to numerical modeling. They have a demonstrated record in O3 research and a strong sense of collaboration and scientific integration (see for example, Krupa et al. 2001). Those are the real technical strengths of the project.
Back to Top