Elevated Carbon Dioxide Creates Noticeably Different Results in Soybean Diseases

With more CO2, plants grow faster and pores close more frequently. Elevated ozone results in weaker plant tissue.

Published on: Jul 5, 2010
Whether or not you agree with climate change, researchers are moving forward with studying how the environment will respond to an atmosphere filled with significantly higher levels of carbon.

One such experiment is the University of Illinois' soybean-free air-concentrating enrichment (SoyFACE) facility in Champaign. Researchers are studying the impact of elevated carbon dioxide, elevated ozone and higher atmospheric temperatures on plant diseases that could challenge crops in these changing conditions.

Darin Eastburn, U of I associate professor of crop sciences, evaluated the effects of elevated carbon dioxide and ozone on three economically important soybean diseases under natural field conditions within the SoyFACE atmosphere.

The diseases downy mildew, Septoria brown spot, and sudden death syndrome were observed from 2005 to 2007 using visual surveys and digital image analysis. While changes in atmospheric composition altered disease expression, the responses of the three pathosystems varied considerably, Eastburn notes.

Elevated carbon dioxide levels are more likely to have a direct effect on plant diseases through changes to the plant hosts rather than the plant pathogens.

"Plants growing in a high carbon dioxide environment tend to grow faster and larger, and they have denser canopies," Eastburn adds. "These dense plant canopies favor the development of some diseases because the low light levels and reduced air circulation allow higher relative humidity levels to develop, and this promotes the growth and sporulation of many plant pathogens."

At the same time, plants grown in high carbon dioxide environments also close their stomata, pores in the leaves that allow the plant to take in carbon dioxide and release oxygen, more often. Because plant pathogens often enter the plant through the stomata, the more frequent closing of the stomata may help prevent some pathogens from getting into the plant.

In elevated ozone, plant growth is inhibited and results in shorter plants with less dense canopies. This can slow the growth and reproduction of certain pathogens. However, ozone also damages plant tissues that can help pathogens infect the plant more easily.

"Elevated levels of carbon dioxide and ozone can make a plant more susceptible to some diseases, but less susceptible to others," Eastburn said. "This is exactly what we've observed in our climate change experiments."

U of I's SoyFACE was the first facility to expose plants to elevated ozone under completely open-air conditions within an agricultural field.

"The SoyFACE facility allowed us to evaluate the influence of natural variability of meteorological factors such as drought and temperature in conjunction with imposed atmospheric composition (elevated carbon dioxide and ozone) on naturally occurring soybean diseases across several growing seasons," Eastburn says.

He believes rising temperatures and changes in rainfall patterns will also affect development of plant disease epidemics.

"In some cases, changes of only a few degrees have allowed plant diseases to become established earlier in the season, resulting in more severe disease epidemics," Eastburn explains. "The ranges of some diseases are expanding as rising temperatures are allowing pathogens to overwinter in regions that were previously too cold for them."

For example, warmer winters may allow kudzu to expand its range northward. Because kudzu is an alternate host for the soybean rust pathogen, one result of rising temperatures may be that soybean rust arrives in Illinois earlier in the soybean growing season.

This research was funded by the National Science Foundation, an SJU Sigma Xi grant, the Illinois Council on Food and Agricultural Research, the Soybean Disease Biotechnology Center, the Illinois Soybean Association, USDA Hatch funds, and the Office of Science, Department of Energy Grant.

Eastburn will share his latest research on global climate change and the implications for future plant disease epidemics at the 2010 U of I Agronomy Day on Thursday, Aug. 19. For more information on Agronomy Day, go to agronomyday.cropsci.illinois.edu.