Elevated levels of carbon dioxide in the atmosphere benefit some plants by making them more tolerant to cold temperatures, Cornell researchers have discovered.

"This could mean earlier spring planting dates for some crops in the future," said David Wolfe, Cornell associate professor in the Department of Fruit and Vegetable Science. "It may also affect the mixture of species in natural plant communities, because only certain plants benefit in this way." The researchers' study, "Elevated carbon dioxide mitigates chilling-induced water stress and photosynthetic reduction during chilling," was published recently in the journal Plant, Cell and Environment (1997 20, 625-632). Steve Boese, instructor at the College of Charleston, Charleston, S.C., and Jeff Melkonian, Cornell post-doctoral researcher, co-authored the paper with Wolfe.

Also, Wolfe will present a poster on this topic at the Plant Biology '97 conference cosponsored by the American and Canadian Societies of Plant Physiology, in Vancouver, Canada, on Aug. 3 and 4.

"Our results are another example of how the increase in carbon dioxide and other greenhouse gases will shake up the plant world," Wolfe said. "Our maps of global vegetation zones will inevitably be altered by these sorts of direct effects on plants, whether or not we also have major changes in climate."

The research was supported by the U.S. Department of Agriculture's Special Grants Agricultural Ecosystems Program.

The researchers have focused much of their attention thus far on two crops, beans and cucumbers, that are among a class of plants that tend to wilt when temperatures dip below about 45 degrees Fahrenheit. They knew from prior experiments that elevated carbon dioxide levels often reduce the rate of water loss from leaves, and they suspected this effect would reduce the amount of chilling damage in these species.

This hypothesis was confirmed by their study. Plants grown and chilled at elevated carbon dioxide levels showed less severe wilting and suffered less permanent leaf damage than plants grown and chilled at current atmospheric carbon dioxide concentrations.

"If carbon dioxide in the atmosphere doubles within the next century as we are expecting," Wolfe explained, "these species may be able to withstand temperatures a few degrees cooler than they do now."

The research is the first to fully document that carbon dioxide can have such an easing effect on chilling damage. Most of the work has been conducted in controlled-environment chambers. The researchers plan to follow up with field experiments and test other plant species.

Wolfe points out that the rapid rise in atmospheric carbon dioxide is still a problem from the standpoint of being an important greenhouse gas that may change our climate in unpredictable ways.

Said Wolfe: "I still think that fossil fuel emissions, the primary culprit in the carbon dioxide rise, are not good for the planet. Many of the other gases that are produced, such as sulfur dioxide, ozone and nitrous oxides can have direct negative effects on plants and humans, for that matter."