More carbon dioxide, a major greenhouse gas in the atmosphere linked with global warming, will stimulate the growth of poison ivy and make it more irritating, a study released on Monday said.

After a six-year study at the Duke University, scientists found that higher atmospheric carbon dioxide increases photosynthesis, water use efficiency, growth, and population biomass of poison ivy, whose scientific name is Toxicodendron radicans.

These findings appeared in the May 29 issue of the Proceedings of the National Academy of Sciences (PNAS).

Contact with poison ivy is one of the most widely reported ailments at poison centers in the United States. Approximately 80 percent of humans develop dermatitis upon exposure to urushiol, a carbon-based active compound in the poison ivy, the researchers said.

Now the plant is widely distributed in North America, Central America, parts of Asia, Bermuda, and the Bahama Islands. It has also been introduced in Europe, South Africa, Australia and New Zealand, where it has become invasive and caused reported cases of contact dermatitis.

In Duke University's Free-Air Carbon Dioxide Enrichment experiment from 1999 to 2004, the researchers found that poison ivy's photosynthesis rose by 77 percent and its water usage efficiency rose by 51 percent when the atmospheric carbon dioxide concentration went up by 20 parts per million (ppm).

Although the average plant biomass in 1999 did not differ significantly between treatments, poison ivy grew faster with carbon dioxide enrichment, the researchers found.

By year 2004, ambient plants averaged some 5.0 grams of dry weight, while elevated carbon dioxide plants averaged 8.1 grams, representing an average annual growth increase of 149 percent in elevated compared to ambient plants, they said.

"This increase is notably larger than the 31 percent average increase in biomass observed for woody plants grown at two times the ambient carbon dioxide concentration under controlled conditions," the researchers added in the paper.

Plants growing in higher carbon dioxide concentration also produce a more allergenic form of urushiol, according the team led by James Clark, a professor at the Duke University.

"Our results indicate that Toxicodendron taxa will become more abundant and more 'toxic' in the future, potentially affecting global forest dynamics and human health," they concluded.

"If Toxicodendron becomes both more abundant and more irritating to sensitive individuals, which include 80 percent of the human population, it is likely that this plant will become a greater health problem in the future."

Source: Xinhua