07/08/1993

Local Research Providing Insight into Global Warming

AUBURN, Ala. - Is the Greenhouse Effect all bad? Maybe not, say Auburn University scientists who are studying the effects of increasing concentrations of carbon dioxide in the atmosphere.

Carbon dioxide is a colorless, odorless gas emitted during respiration and when organic material breaks down. While carbon dioxide is a normal component of the atmosphere, concentrations of this gas have been increasing through the years and may be causing a global warming trend -- also known as the Greenhouse Effect. Some scientists theorize this warming trend will cause great stress to life on Earth.

"Research has shown that since 1958 the amount of carbon dioxide in the atmosphere has been indisputably rising - going up about 1.5 to 2 parts per million per year," said Brett Runion, research associate in Auburn's School of Forestry who has been cooperating on a carbon dioxide study.

"The whole global warming theory is a good hypothesis and needs to be tested, but right now it is just a theory. Most of it is based on computer models, not on hard facts," added Runion. Research conducted at Auburn may provide more concrete facts on this trend.

Runion and other scientists working in the Alabama Agricultural Experiment Station and the U.S. Department of Agriculture-Agricultural Research Service are exploring how rising atmospheric carbon dioxide affects plants.

"Carbon dioxide is essential to plant life," said Runion. "Plants take carbon dioxide out of the air to use with water and sunlight in photosynthesis and turn these ingredients into oxygen and sugar. Because of this, increased levels of carbon dioxide should have some effect on the growth and productivity of plants."

To test this, open-top chambers have been erected at the USDA's National Soil Dynamics Laboratory in Auburn and at other locations. Within these chambers, longleaf pine seedlings, grain sorghum, and soybeans are exposed to different levels of carbon dioxide and the plants' responses are evaluated. The project also includes work in Arizona with cotton and wheat and in the Chesapeake Bay area in a salt marsh where native plant species are being evaluated.

Results suggest that extra carbon dioxide in the atmosphere increases photosynthesis for many plants. "Crop plants tend to grow larger and accumulate more starches and sugars. The plants also are using less water to reach a relative size. On a field-wide basis, plants are using as much water, but they are producing more yield from that water," Runion explained.

Dark respiration is another facet of their study. "Plants take up carbon dioxide during the day through photosynthesis and give off carbon dioxide during the night through respiration. That's called dark respiration," explained Runion. "There is some evidence that dark respiration is reduced in a number of species, which indicates that more of the carbon dioxide they are taking up is remaining in the plant or going out through the roots."

So what does this mean? "In row crops and monoculture situations, these results suggest that elevated carbon dioxide can be viewed as an asset," said Runion. "In other words, there could be something good about the "global warming' effect."

However, Runion noted that in natural plant communities, such as the salt marshes, where several species of plants are growing together elevated carbon dioxide concentrations may be harmful.

"Individual plant species respond very differently to elevated carbon dioxide," he explained. "In a natural plant community, there will be several different species of plants growing in the same area. If carbon dioxide aids the growth of some plants, that may limit the ability of other species to compete in a natural environment."

Runion is quick to note that these results are a long way from deciphering the full effects of carbon dioxide on plant life, and ultimately on animal life. However, the research is expanding scientific understanding of changes in the environment.

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Auburn, AL 36849
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Contact Jamie Creamer, 334-844-2783 or jcreamer@auburn.edu
Contact Katie Jackson, 334-844-5886 or smithcl@auburn.edu

July 8, 1993