RESEARCH Science Agriculture

Increasing carbon dioxide relieves drought stress in corn, researchers say

Jim Barlow, Life Sciences Editor
(217) 333-5802; jebarlow@uiuc.edu

10/7/03

CHAMPAIGN, Ill. — Although rising ozone levels already reduce soybean yields, a study of the crop grown in projected 2030 levels has harvested more troubling results – a 20 percent yield loss – say scientists at the University of Illinois at Urbana-Champaign.

Assuming gradual rises in ozone levels, the findings suggest that the U.S. soybean industry may suffer an additional $21 million loss each year for the next 30 years. However, researchers say, rising carbon dioxide levels may reduce some ozone effects, but other global warming factors cloud their ability to get a clear view of the future.

Findings of a study done in the 2002 growing season were presented today by Patrick B. Morgan, an Illinois doctoral student in the department of plant biology, at Plant Biology 2003, the annual meeting of the American Society of Plant Biologists, in Hawaii. Morgan’s work was specially selected by the society for presentation at the meeting.

Ozone levels in industrialized nations have been rising annually by 0.5 percent to 2.5 percent, with the highest levels occurring in the northern hemisphere. At Illinois, researchers from around the world are conducting the only open-air experiments, exposing crops to anticipated future levels of ozone and carbon dioxide.

Soybean losses begin at ozone concentrations of 40 parts per billion. In Illinois, the average concentration is already 64 parts per billion with occasional daily spikes as high as 120 parts per billion, Morgan said. In his study, experimental soybeans, a cultivar commonly grown in the Midwest, were exposed to an average concentration of 75 parts per billion (coinciding with a 20 percent increase projected by the Intergovernmental Panel on Climate Change), while the average for control soybeans was 62 parts per billion.

Illinois researchers found that soybeans suffer significant losses in leaf photosynthesis as leaves age and, more dramatically, in overall biomass.

The latter damages resulted in fewer numbers of seeds and pods and a reduction in seed weight – factors that translate into reduced harvests, said Morgan, who monitored physiological changes in regular intervals during the growing season.

"What we found was surprising and a bit shocking – with a 20 percent rise in ozone exposure we also saw a 20 percent drop in yield," said Stephen P. Long, a professor in the departments of plant biology and crop sciences at Illinois and Morgan’s doctoral adviser. "Ozone levels are already suppressing soybean yields each year by about 20 percent based on projections of the USDA and the U.S. Environmental Protection Agency.

"Our experiment gives us a good indication of what additional loss we may be seeing over the next few decades," Long said. "It predicts about a 0.4 percent loss each year, which doesn’t sound like very much, but it is enough to steal profits away. Ozone levels are highly variable, depending on weather, so with this variability a 20 percent increase in ozone could occur next year."

Ozone enters plants through stomata (tiny pores in the epidermal layer of leaves) and reduces photosynthesis. Evaporation of moisture also occurs through these pores. Carbon dioxide, researchers theorize, constricts the pores, repelling ozone and maintaining moisture. Illinois researchers are trying to understand the mechanism of damage to photosynthesis so that they could take steps – through breeding, for example – to protect plants.

The findings of the 2002 project concur with 53 previous studies that used laboratory approaches to examine ozone impacts on soybeans, Morgan said. A comprehensive data analysis of the earlier studies showed that ozone’s damage to photosynthesis is not as great as that done to crop biomass. However, the data showed up to 25 percent losses in harvestable yield in ozone concentrations of 60 parts per billion.

Morgan, Elizabeth A. Ainsworth, a doctoral student in crop sciences, and Long performed the analysis, which will appear in the journal Plant, Cell and Environment.

The 2002 study was done by Morgan, Long, German A. Bollero, a professor of crop sciences, and Carl J. Bernacchi, also a professor of crop sciences and scientist with the USDA-Agricultural Research Service.

The research was conducted at the SoyFACE (Free Air Concentration Enrichment) facilities on the south end of campus. Within 70-foot octagon-shaped rings, ABS plastic pipes deliver at crop level a precisely regulated flow of either carbon dioxide and/or ozone from 50-ton solar-powered tanks. Control rings also surround equal amounts of non-altered crops, which grow in normal conditions, without gases, for comparison purposes.

Long is one of the lead researchers of SoyFACE.
Construction began in 2000; research began the next spring. SoyFACE comprises more than 30 research groups with participants from 18 countries. Funding is provided by the Illinois Council for Food and Agricultural Research, the U.S. Department of Agriculture, the Department of Energy’s Argonne National Laboratory, Archer Daniels Midland Co. and Pioneer Hi-Bred International Inc.