Research by an international team of environmental scientists from the United Kingdom, Belgium and United States, including Indiana University, has found that plants that associate with one type of symbiotic fungi grow bigger in response to high levels of carbon dioxide, or CO2, in the atmosphere, but plants that associate with the other major type of symbiotic fungi do not. The study, which appears online today in the journal Science, calls into question whether the 'greening of the Earth' that results from carbon dioxide stimulation of plant growth -- often called the "CO2 fertilization effect" -- will persist as fossil fuel emissions continue to rise globally.

"Pumping extra carbon dioxide into a greenhouse is a common tactic to stimulate plant growth, but nature is much more complex than a greenhouse," said Richard Phillips, associate professor in the IU College of Arts and Sciences' Department of Biology, who is a co-author on the study. "So, there is great debate about whether pumping carbon dioxide into the atmosphere through fossil fuel combustion stimulates plant growth in nature, where soil nutrient levels are typically much lower than in a greenhouse."

Fungi that form symbiotic relationships with plants are called mycorrhizal fungi. Over 90 percent of all plant life on Earth associates with mycorrhizal fungi, which provide plants with soil nutrients in exchange for plant carbohydrates. 

"While researchers have long known that mycorrhizal fungi play an essential role in the growth and health of plants, their role in helping ecosystems store carbon has never been investigated on such a broad scale -- until now," said second-year PhD student Cesar Terrer of Imperial College London, who is first author on the paper. "Our analysis is the first to demonstrate that only plants that associate with a certain type of fungal partner - one that helps them acquire nitrogen from soil - are likely to grow bigger as carbon dioxide levels rise."

Other authors are on the study are Colin Prentice of Imperial College London; Sara Vicca of the University of Antwerp, Belgium; and Bruce A. Hungate of the Northern Arizona University.