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United States Department of Agriculture

Agricultural Research Service

You are here: ARS Home / Research / National Programs / National Program 203 : Air Quality / Component IV: Ozone Impacts
National Program 203: Air Quality
Component IV: Ozone Impacts
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1 - Introduction
2 - Effects of Ozone on Yield and Product Quality
3 - Mechanisms of Ozone Response
4 - Ozone-Tolerant Crops
5 - Effects of Ozone on Pests and Parasites


The air pollutant ozone is toxic to plants and occurs at sufficiently high concentrations in many parts of the country to cause visible symptoms of injury and to suppress the growth of many common crops. Ozone is a secondary pollutant that forms from nitrogen oxides and hydrocarbons that originate mostly in populated and industrialized areas, but can be transported hundreds of miles before reacting to form ozone. Some of the most productive agricultural areas in the U.S. are exposed to elevated ozone, and concentrations in rural areas are projected to increase. Data on emissions of precursors and their reaction in the atmosphere to form ozone and its subsequent transport in the atmosphere, as well as measurement of ambient ozone concentrations nationally, are readily available from other agencies such as EPA and NOAA.

Tropospheric ozone, that is, ozone occurring in that part of the atmosphere that is within 7 to 10 miles of the earth=s surface, disrupts processes that can significantly suppress photosynthesis of many plant species. It can cause significant yield losses in common crops such as soybean, cotton, and wheat. Estimates indicate ozone-induced yield losses at current concentrations ranging from negligible to approximately 20% or more in some areas, depending on the crop species and environmental conditions during plant growth and exposure.

Plants grown in elevated ozone exhibit extensive biochemical and physiological differences from plants grown at lower concentrations. For example, ozone induces common wound and defense responses. In some cases, compounds are increased that may protect the plants from further ozone-induced injury. Changes in the chemical composition of ozone-stressed plants may affect plant-pest interactions and nutrient cycling from decomposing plant debris as well. Exposure of plants to ozone can alter the extent of infestation by insect pests. Thus, biochemical changes induced in plants by these gases may have impacts on crop systems beyond direct effects on growth. Estimates of the impact of greenhouse gases on agriculture will be inaccurate unless such effects on noncrop organisms and their interactions with crop plants are considered.

Plant response to ozone is controlled genetically. Species and genotypes (cultivars, clones) within a species may exhibit a range of responses. Capitalizing on this genetic variability is one possible way to minimize the negative impacts of ozone on crop production. To incorporate these traits efficiently into crops that are otherwise desirable agronomically, the biochemical and physiological attributes that confer these traits must be determined. Collections of plants exist (e.g., snap bean genotypes and white clover clones) that exhibit a wide range in response to ozone; these will be useful as model systems for such studies. This research will contribute to development of genotypes with improved performance under ozone polluted conditions.

Effects of ozone on plant growth and biochemistry are well-documented, but impacts of this gas on crop production systems in the future currently cannot be predicted with a high degree of confidence. Uncertainties are due to the complexity of interactions among plants, gas concentrations, environmental conditions, and noncrop organisms. Studies of these interactions are at an early stage, but an improved understanding of the effects of the gases in combination and in interaction with other factors in crop systems is required before the net effect on agricultural commodities in the U.S. can be defined.

This research meets a national need for developing agricultural management strategies to respond to atmospheric change. Ozone concentrations in the atmosphere will continue to increase in the foreseeable future. Cost-effective approaches to mitigate negative effects of this gas are not currently available, and economically feasible management options need to be identified. These options are most likely to be identified by developing a thorough understanding of the plant physiological mechanisms of response, establishing the genetic/biochemical basis of stress resistance, and determining the relevant interactions of the gas effects with environment and noncrop organisms. Ozone toxicity resembles oxidative stresses caused by other environmental phenomena of importance to agriculture, such as chilling, high light intensity, herbicides, pathogens, and other pollutants. Thus, the knowledge gained from this work will have a broader application than for ozone pollution alone.

This research will show the degree of impact on agricultural production to be expected from changes in air quality and thus will indicate the level of response needed to ameliorate the effects. The agricultural community, including federal and state extension personnel, the Economic Research Service (ERS), growers, cooperating scientists, and the scientific community are users of the research results. Plant production industries are recognizing increasingly that atmospheric contaminants affect their products. Results of this research will continue to benefit regulatory and action agencies and policymakers. The Federal Clean Air Act (Sections 108 and 109) requires the periodic evaluation of data on air quality effects on public welfare (Secondary Standard) for setting National Ambient Air Quality Standards. This research will respond to that mandate by providing the best available information on ozone effects on crops.

This research also will be a major source of information used by EPA to develop the criteria document 'Air Quality Criteria for Ozone and Related Photochemical Oxidants.' This document is required to evaluate and set the National Ambient Air Quality Standards for protection of public health and welfare from adverse effects of photochemical oxidants. Recent meetingswith EPA staff indicated a continuing need for expanded and updated data for ozone effects on crops. Furthermore, the research will contribute to the information base needed to assess national and international policies for control of anthropogenic emissions.


Quality crop production free of limitations caused by tropospheric ozone


Identify ozone-tolerant crop species and varieties, response mechanisms to select or develop tolerant varieties, and production methods that minimize ozone-induced limitations on crop production and quality; and develop science-based information required for sound policy and regulatory decisions.

Table 5. ARS Research Locations Contributing to Component IV of the Air Quality National Program--Ozone Impacts


Component Problem Areas



Effects of Ozone on Yield & Product Quality

Mechanisms of Ozone Response

Ozone- Tolerant Crop Plants

Effects of Ozone on Pests & Parasites















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Last Modified: 10/28/2008
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