Increasing carbon dioxide relieves drought stress in corn

Increasing carbon dioxide in the atmosphere will benefit photosynthesis in U.S. corn crops in the future by relieving drought stress, say researchers at the University of Illinois at Urbana-Champaign.

According to preliminary findings of a new study — being released this week in Hawaii during Plant Biology 2003, the annual meeting of the American Society of Plant Biologists — photosynthesis of maize on average increased by 10 percent under projected carbon dioxide conditions in the year 2050.

“Carbon dioxide in isolation is good news for the farmers, but unfortunately such conditions won’t be in isolation from other factors, so it isn’t known how significant these findings may be,” said Stephen P. Long, a professor of plant biology and crop sciences.

Long is a lead researcher of SoyFACE (Free Air Concentration Enrichment), a long-term project and the only open-air experiment in the world looking at the effect of future levels of ozone and carbon dioxide gases on agricultural crops.

The corn photosynthesis findings are being exhibited by Andrew Leakey, a Fulbright scholar from Scotland who is conducting research in the SoyFACE fields with Long and with Carl Bernacchi and Donald Ort, both professors of plant biology at Illinois and scientists with the USDA/Agricultural Research Service.

Corn is among the 1 percent of plants that use the carbon-dioxide efficient photosynthesis system known as C4. Scientists had theorized that C4 plants would not respond to more carbon dioxide in the air, because the gas is internally concentrated by the leaf – essentially a fuel-injected photosynthesis, Leakey said.

However, Leakey found that in a carbon dioxide concentration of 550 parts per million, carbon fixation in the leaves indeed rose in association with greater intercellular carbon dioxide and enhanced water use efficiency.

The 2002 growing season, when the research was conducted, was considered a typical one in terms of weather. However, at the end of a dry spell in June, Leakey found, carbon fixation increased under elevated carbon dioxide as much as 41 percent.

Since carbon dioxide serves to close the stomata, which are tiny pores in the epidermal layer of leaves, the jump in photosynthesis likely resulted from the plant maintaining higher water content in the leaves during the dry period, Long said.

The improvement in corn growth could be offset by the effects of rising ozone levels and other global warming factors, the researchers are quick to point out. While elevated ozone is part of the SoyFACE technology, corn has not yet been exposed to it. In soybeans, initial exposure to carbon dioxide led to increased yields that were later dramatically reversed by the effects of ozone.

The SoyFACE research area on the south end of campus features 70-foot octagon-shaped plots in which 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 surround equal amounts of control crops, which grow in normal conditions, without gases, for comparison purposes.

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 International Arid Lands Consortium of Astra-Zeneca, United Kingdom, the U.S. Department of Energy’s Argonne National Laboratory, Archer Daniels Midland Co. and Pioneer Hi-Bred International Inc.