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Title: GROWTH AND YIELD RESPONSES OF WINTER WHEAT TO MIXTURES OF OZONE AND CARBON DIOXIDE

Author
item Heagle, Allen
item Miller, Joseph
item PURSLEY, WALT - NORTH CAROLINA STATE UNIV

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: The world's human population is expected to increase from the present 6 billion to over 9 billion by the year 2050. Whether or not world food supply will keep pace with world population is not known. Population increase has been accompanied by increased use of fossil fuels which has affected air quality in ways important to agricultural crops. An apparent positive change is increased atmospheric carbon dioxide (CO2) which is expected to double within the next 100 years. Because CO2 is required for photosynthesis, elevated CO2 is expected to enhance crop yields. A negative change is the dramatic increase in ground level ozone (O3). Elevated O3 stresses plants and decreases crop yield. Research to measure the positive effects of CO2 and negative effects of O3 on crop yield has traditionally considered each gas separately. The possibility that plant response to elevated CO2 might affect response to O3, or vice versa, has mostly been ignored. This question was addressed for wheat by examining effects of simultaneous season-long exposure to a range of O3 and CO2 concentrations. When plants were exposed to elevated O3 alone, leaves were injured and yield was decreased. However, when plants were exposed simultaneously to elevated O3 and elevated CO2, the CO2 protected the plants and O3 did not decrease yield. Moreover, elevated CO2 did not increase wheat yield when plants were grown at the lowest O3 concentration. Our previous research with soybean, cotton, and rice also showed comparatively little or no yield increase due to elevated CO2 in the absence of O3 stress. The results raise concern that inputs to models to predict future food supply might be overestimating the impact of CO2 enrichment. Outputs from these models can be improved by using data corrected for O3 concentration.

Technical Abstract: Current concentrations of ground level ozone (O3) can cause plant stress and decreased yield, whereas elevated CO2 generally enhances growth and yield. Until recently however, few studies have considered whether CO2 enrichment can affect plant response to O3 or vice-versa. We examined effects of simultaneous exposure to O3 and CO2 on growth and yield of soft red winter wheat. Plants were exposed from emergence to maturity in open-top field chambers to all combinations of three CO2 and three O3 concentrations. The CO2 treatments were 380, 540, and 700 uL L-1 for 24 h d-1. The O3 treatments were 27, 45, and 90 nL L-1 for 12 h d-1. In the first year, eight cultivars with widely different genetic background were tested. None of them showed yield increase caused by elevated CO2 when plants were were grown at the lowest O3 level. Coker 9835 was among the most resistant cultivars to O3, whereas Coker 9904 was the most sensitive. These two cultivars were tested in the second year. Foliar injury caused by O3 was suppressed by elevated CO2. Elevated CO2 increased growth and yield for plants grown at 45 and 90 nL L-1 O3 but not for plants grown at 27 nL L-1 O3 . Yield of the sensitive cultivar was suppressed more by O3 than yield of the resistant cultivar. This differential sensitivity to O3, resulted in a greater effect of elevated CO2 on yield of the sensitive than of the resistant cultivar. Significant 3-way interactions (cultivar x O3 x CO2) occurred for all growth and yield measures. The results indicate that elevated CO2 will cause little or no yield increase of winter wheat for plants grown under non-stressed conditions. They also show the need to be aware of possible interactions between O3 and CO2 in studies to determine effects of O3 or CO2 on plant systems.