The study showed when either phosphorus or nitrogen -- both of which occur naturally in the rain forest soils -- were added to forest plots in Costa Rica, they caused soil microbes to increase their CO2 emissions to the atmosphere by about 20 percent annually, said Cory Cleveland of CU's Institute of Arctic and Alpine Research.

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 CO2, the primary greenhouse gas that has increased by roughly 33 percent since the Industrial Revolution began about 1760.

A paper on the subject by Cleveland and CU-Boulder Associate Professor Alan Townsend of INSTAAR is being published the week of June 19 in the Proceedings of the National Academy of Sciences. The National Science Foundation funded the study.

"One big question is how tropical rain forests are responding to climate change," said Cleveland, an INSTAAR research associate who led the study. "What we have demonstrated is that even small changes in nutrients could have a similarly profound impact on the release of CO2 from tropical forest soils."

Tropical forests contain up to 40 percent of the carbon stored on Earth's continents and account for at least one-third of the annual exchange of CO2 between the biosphere and the atmosphere, said Cleveland. Earth's soils are believed to store several times more carbon than all of the planet's vegetation.

"This is the first time anyone has taken a close look at how changes in key nutrients may alter soil CO2 emissions in tropical forests," said Clevel
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Contact: Cory Cleveland
cory.cleveland@colorado.edu
303-735-7926
University of Colorado at Boulder
19-Jun-2006