To find out, a UC scientist at the Kearney Agricultural Center near Parlier has undertaken a multi-year study aimed not at the effect of ozone on yield or plant vigor, but to determine what happens to plant tissues when they grow in the presence of ozone.

"Ozone is the most important plant damaging air pollutant in the world," said UC Riverside extension air quality effects specialist David Grantz. "There is no question that ozone is damaging plants and reducing agricultural yields, though often we cannot say exactly by how much in any one crop. But if we want to develop ways to understand this damage and to overcome ozone's impact - assuming we can't clean up the air - we have to know what it is doing to plant tissues."

Ozone is a molecule of three oxygen atoms bound together. The ozone in San Joaquin Valley air, for the most part, is created by the combination of automobile and industrial exhaust with heat and sunlight. In lungs, ozone damages air sacs that are important for gas exchange. Repeated exposure to ozone can inflame lung tissues and cause respiratory problems. Grantz, who is also the director of the Kearney Agricultural Center, said while it is clear that ozone inhibits plants' photosynthesis so less sugar is available for plant growth, it also appears to inhibit the movement of sugars from the leaves to the roots.

His current research is evaluating the importance of these two effects on plant growth. To conduct the study, Grantz constructed 10 gazebo-sized plastic and aluminum open-topped chambers on a test plot at the Kearney Agricultural Center. Six chambers house small potted Pima cotton and cantaloupe plants that are irrigated and fed through drip tubing. Three additional chambers -- which monitor the effects of various levels of ozone on a variety of agricultural and landscape plants, such as petunia, grape, peach, plum and pistachio -- are for demonstration purposes and not part of the experiment. One third of the chambers is subjected to ozone levels similar to those experienced on a bad day in the San Joaquin Valley around Parlier, approximately 150 parts per million at the 3 p.m. peak time.

 "These values were picked to match the highest ozone days in recent years," Grantz said.

Another third of the chambers simulates ozone levels that might be in the valley's future. The amount is 1.6 times higher than the current highest ozone days. Control plants are grown with ozone-free air. Grantz and his research assistants are taking detailed measurements on the young Pima cotton and cantaloupe plants. Cantaloupe and Pima cotton were selected because they transport sugar in two distinct ways that are representative of many plants' sugar transport systems.

After several weeks of growth, the plant roots are washed free of the scintered clay (similar to kitty litter) in which they are being grown. The plant and roots are scanned by a computer with software that calculates the plants' root length and thickness and the surface area available to absorb nutrients. Other data is collected using a sophisticated instrument in the field. The scientists clamp on a single leaf to measure the rate of photosynthesis and amount of sugars being made by the leaf. The instrument also indicates how wide the leaf pores are, which helps to control water loss and ozone uptake into the plant. Both are indicators of plant growth and respiration. In addition, root tips are examined with a computerized respiration measurement system to determine the amount of oxygen they use.

These types of mechanistic data can contribute to computer models of ozone's effect on plants. Ultimately, Grantz said, the research results and models can suggest plant management and breeding objectives to improve plant resistance to ozone. The information generated in the Kearney experiments can also be used to understand ozone impacts on forests and other native vegetation, and crop losses in other areas associated with ozone. Grantz' research and educational efforts are funded by grants from the USDA and California Air Resources Board.