Results of the research, conducted by Cory Cleveland and CU scientist Alan Townsend, are published this week in the journal Proceedings of the National Academy of Sciences.

"The large change in carbon dioxide emissions from tropical forest soils due to soil nutrients is a new dimension in understanding these important ecosystems," said Martyn Caldwell, program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research.

"Tropical rainforests have received considerable attention related to the global carbon balance, but that has largely revolved around rainforest vegetation and its ability to 'take up' carbon dioxide," said Caldwell. "This is a new look at tropical rainforests and their relationship to carbon dioxide levels on Earth."

The study showed that when phosphorus or nitrogen -- which occur naturally in rain forest soils -- were added to forest plots in Costa Rica, they caused an increase in carbon dioxide emissions to the atmosphere by about 20 percent annually, said Cleveland.

"The study is important because human activities are changing the amount of phosphorus and nitrogen in ecosystems all over the globe, including the tropics," Cleveland said. "Tropical rain forests play a dominant role on Earth in regulating atmospheric carbon dioxide."

One big question, said Cleveland, "is how tropical rain forests are responding to climate change. What we have demonstrated is that even small changes in nutrients could have a profound impact on the release of carbon dioxide from tropical forest soils."

The study, which took place in 2004 and 2005 in Costa Rica's Golfo Dulce Forest Reserve, included a series of 25 meter-square plots t
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Contact: Cheryl Dybas
cdybas@nsf.gov
703-292-7734
National Science Foundation
20-Jun-2006