Carbon Dioxide and Crop Production

By George Grow

This is Bill White with the VOA Special English AGRICULTURE REPORT.

Human activities are producing increasing levels of carbon dioxide and other gases into the Earth's atmosphere. These gases are trapping more heat. Scientists say the rising temperatures will have a major effect on the environment and agriculture.

Rising carbon dioxide levels cause increased production of some crops. Scientists have developed computer programs to show how these changes will affect the world food supply.

However, studies by the United States Department of Agriculture suggest some computer estimates may be wrong. Scientists with the Agricultural Research Service say that another gas -- ozone -- should be included in the computer programs. Ozone in the lower atmosphere is an air pollutant. It has been shown to damage plant tissue and decrease crop production.

Joseph Miller is head of an Agricultural Research Service study group in Raleigh, North Carolina. Mr. Miller notes that earlier studies to measure the effects of carbon dioxide and ozone on crops have examined each gas separately.

He and his team have been combining the two gases in tests on several kinds of crops. Their results suggest that crop production in increased carbon dioxide environments may not be as high as suggested. They say the extra carbon dioxide may, in fact, prevent crop losses caused by ozone.

The researchers found that rising carbon dioxide levels combined with low ozone levels do not always cause increased plant growth. They say extra carbon dioxide causes some added growth because the plants have more food for photosynthesis. Photosynthesis is the natural process that plants use to change sunlight into energy.

The researchers observed this when the two gases were combined in field tests of soybeans, winter wheat, rice and cotton. Mr. Miller notes that soybeans and cotton are affected by ozone. Some kinds of wheat and rice also suffer damage and produce less in tests with high levels of ozone.

The researchers say the extra carbon dioxide partly closes small openings on the leaf through which the plant exchanges gases. This reduces the amount of ozone entering the leaf and water vapor released by the leaf. As a result, they say, carbon dioxide helps plants growing where there is too much ozone or not enough water. The findings are reported in Agricultural Research magazine.

This AGRICULTURE REPORT was written by George Grow. This is Bill White.