'Ozone Puts New Wrinkle in CO2 Yield Projection' was published in the April 2000 issue of Agricultural Research magazine. stimulates growth and increases yield in a variety of food and fiber crops. But will yields surge enough to feed the world's population of 9 billion expected by 2050? To find out, scientists have developed computer models for each of the major crops—mainly grains. 'We use models to project the effects of both rising CO and projected climate changes on world food supply,' says Cynthia Rosenzweig. She heads the project at NASA's Goddard Institute for Space Studies at Columbia University in New York City. enrichment will stimulate growth. The scientists are proposing that another gas be included in the models: the air pollutant ozone. This oxidizing agent damages plant tissue and decreases crop yield. and the negative effects of ground-level ozone on crop yield have traditionally looked at each gas separately,' says plant physiologist Joseph E. Miller. He is the head of ARS' Air Quality-Plant Growth and Development Unit in Raleigh, North Carolina. Miller and colleagues Allen S. Heagle, Edwin L. Fiscus, and Fitzgerald L. Booker have been combining the two gases in various concentrations on several crops throughout the growing season. The results suggest that much of the CO So far, the researchers have seen this interaction in field tests of soybeans, winter wheat, rice, and cotton and in greenhouse tests of snap bean and white clover—a forage crop. Each crop or variety responds to a greater or lesser degree, depending on its sensitivity to each gas, but the trend is always the same. Soybeans are quite sensitive to ozone, as is cotton, Miller notes. And some varieties of wheat and rice also suffer damage and yield loss under high ozone. partially closes the leaf pores, or stomates, through which plants exchange gases. This reduces the ozone that gets in and the water vapor that gets out. 'So if plants are under ozone or water stress, you'll get a greater response to CO researcher Bruce A. Kimball scratching his head. Kimball, who heads ARS' Environmental and Plant Dynamics Research Unit in Phoenix, Arizona, says that many of the studies reporting yield increases from CO stimulation [the Raleigh researchers] are getting in low ozone is generally lower than what is reported in the literature,' says Kimball. Steven J. Britz, who heads the Climate Stress Laboratory in Beltsville, Maryland, adds, 'The Raleigh experiments are a good example that the field of CO Source.