Growth, Radiation Use Efficiency, and Canopy Reflectance of Wheat and Corn Grown under Elevated Ozone and Carbon Dioxide Atmospheres

Es t ima te s of increases in future agricultural production in response to increases in carbon dioxide (C02) concentrations in the atmosphere are often based on the beneficial physiological effect of C02 enrichment on plant growth, especially in Ca plants. However, these estimates fail to consider the negative impact of ozone (03) air pollution on crop production. Increases in tropospheric concentrations of both gases, CO~ and 03, have been observed over the past century, and both are predicted to continue to increase at even higher rates in the near future to levels when they may have a significant impact on agricultural production. Field studies with wheat (Friticum aestivum L.) in 1991 and 1992, and corn (Zea mays L.) in 1991 were conducted using open-top chambers to mimic atmospheric concentrations of CO~ (~ 500 IzL~ C02) and Oa ( 40 nL L1 03 above ambient air [03] during 7 h day1, 5 days week1) that are predicted to occur at the Earth's surface during the first half of the 21st century. Wheat and corn (C3 vs. C4) produced clearly different responses to COe enrichment, but similar responses to 03 exposure. In wheat, 03 exposure led to reduced grain yield, biomass, and radiation use efficiency (RUE, phytomass production per unit of energy received); in both years; but reduction in accumulated absorbed photosynthetically active radiation (AAPAR)