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Mailed 7/30/95


Trees Increase Their Rate of Photosynthesis

Upton, NY - Scientists at the U.S. Department of Energy's Brookhaven National Laboratory and at Duke University report that loblolly pine trees grown in a 21st century atmosphere of increased carbon dioxide (CO2) show a marked increase in their rate of photosynthesis.

In a season-long experiment, the researchers found that the rate of photosynthesis in pines growing in elevated CO2 was 65 percent higher than in pines growing in the present CO2 environment. They also found that the trees' water consumption did not change in response to the elevated CO2, unlike the decrease typically seen in crops and herbaceous plants.

David Ellsworth, tree physiologist with Brookhaven Lab, said, "Ours is the only study of this sort that has ever been conducted in a forest, yet one-third of Earth's land mass is covered by forests. Up to now, we have not been able to study how an entire forest would respond to increased CO2."

Principal researchers in the study also include tree physiologist Ram Oren, of Duke University, and ecologist George Hendrey, also of Brookhaven. Their work is reported in a paper soon to be published in the journal Oecologia. Ellsworth is scheduled to present the findings on August 1, at the annual meeting of the Ecological Society of America in Snowbird, Utah.

About FACE

The forest experiment was the first use of FACE technology in a forest environment. FACE, which stands for free-air carbon-dioxide enrichment, was developed by Dr. Hendrey and colleagues at Brookhaven to study effects of enhanced CO2 on plants in their natural environment. Only such experiments, conducted in open air rather than in greenhouses or any other types of enclosures, can mimic "real world" conditions in order to simulate how entire ecosystems will cope with the predicted higher-CO2 atmosphere of the next century.

Levels of CO2 in the atmosphere have risen from 280 parts per million (ppm) at the beginning of the Industrial Revolution in the late 18th century to 355 ppm today, an increase of over 25 percent, primarily because of increased fossil-fuel combustion. Scientists expect that the current level will double some time in the next century.

Dr. Hendrey and colleagues have previously used FACE to evaluate effects of increased CO2 on agricultural crops in Mississippi and Arizona, and on grassland in Switzerland.

In the FACE system, an array of vertical pipes encircling the test area releases CO2 in a computer-controlled mixture with ambient air. The computer measures wind direction, wind speed and the CO2 concentration in the center of the array, and uses this information to adjust the rate of gas to be released on a second-to-second basis. The resulting environment is as close as practical to the atmosphere expected to prevail in the middle of the 21st century.

In the Duke Forest

The forest experiment was carried out on mature loblolly pine trees in North Carolina, in a forest owned by Duke. Used for timber, loblolly pines are the mainstay of the lumber industry in the Southeast.

While increased photosynthesis may result in faster-growing trees and, hence, more wood, the researchers caution against viewing their results as entirely good news. It is not yet clear that the extra photosynthesis will be reflected in faster growth. Said Dr. Ellsworth, "These are early findings, and there are many questions still unanswered. What about competition from other trees? Will the forest outstrip the soil's capacity to support enhanced growth? Would faster-growing wood be more brittle? It's not so simple."

The Experiment Ahead

Already begun is a much broader, multi-year experiment. Besides continuing the tree physiology work, this next experiment will include soil and atmospheric studies. Dozens of ecologists and plant biologists will work at the Duke forest site, collecting data not only on loblolly pines, but also on sweetgums, dogwoods, honeysuckle, junipers, and microbes and soils. Results from the study will be used in global computer models to predict the role of vegetation in future CO2 exchange with the atmosphere.

The FACE approach gives many scientists access to a large facility that encompasses hundreds of individual plants in an intact ecosystem. This reduces the cost per scientist dramatically. The net effect is an economical way to build an understanding of how a particular ecosystem will respond to rising levels of CO2.

FACE research is supported by the Department of Energy's Office of Health and Environmental Research, Ecological Research Division. Brookhaven National Laboratory carries out basic and applied research in the physical, biomedical and environmental sciences and in selected energy technologies. Brookhaven is operated by Associated Universities, Inc., a nonprofit research management organization, under contract to the Department of Energy.