Cory Cleveland and Alan Townsend have completed a study of tropical forest soils showing that even small changes in nutrients could have a profound impact on the release of CO2. The new study, which took place in 2004 and 2005 in Costa Rica's Golfo Dulce Forest Reserve, included a series of 25 meter-square plots that were fertilized with phosphorus, nitrogen, or a combination of the two. Soil respiration was measured using plastic tubes in the ground running into vented, closed chambers. The fertilized plots yielded surprisingly large releases of CO2 to the atmosphere. The new results have global implications because human activity has changed the availability of both phosphorus and nitrogen over many parts of the tropics. Moreover, Earth's soils are believed to store several times more carbon than all of the planet's vegetation.
Phosphorus and many other nutrients are regularly transported around the Earth by global wind patterns, sometimes riding on huge transcontinental dust clouds. There is strong evidence that humans are increasing the size of these dust clouds as both land-use patterns and climate change, which in turn can change the availability of nutrients to forests. Nitrogen pollution also is increasing around the world, including in tropical forests, a result of fossil-fuel combustion and crop fertilization activities. Human activity has changed the availability of nitrogen all over the world, especially in the last 50 years.
This research was funded by the National Science Foundation (NSF) and featured on the NSF News website on 20 June.