Feb. 15, 2017
The Tropics are typically considered the areas of land within the Tropics of Cancer (23° 28’N) and the Tropics of Capricorn (23° 28’S); basically places where is no winter. This region encompasses a range of different types of tropical ecosystems: deserts, grasslands, savannas, and perhaps most iconic, rainforests (Osborne, 2000).
“Tropical rain forests: ‘the greatest celebration of life on Earth’ – Norman Myers
Tropical forests contain about two-thirds of all terrestrial biomass (Pan et al., 2013), meaning that they store a lot of carbon and act as like a sponge for CO2. However, in climate models they are among the most poorly represented. The mission of the Next Generation Ecosystem Experiment – Tropics project (NGEE-Tropics) and also the Amazon Free Air CO2 Enrichment project (Amazon FACE) is to understand what factors influence the exchange of CO2 between tropical rainforests and the atmosphere. Essentially, we cannot and should not model everything so what are the physiological, biological, and geochemical factors that are most important to determining how much CO2 goes into tropical forests and how much goes out?
Free Air CO2 Enrichment (FACE) experiments involve infusing parts of the forest encircled by gigantic towers with CO2. This figure is showing that wood increment is increasing with CO2, up to a certain point. Then we see that plots that wee fertilized with nitrogen continued growing but plots without declined in growth.
The Smithsonian Tropical Research Institute (STRI) in Panama exists to understand biological diversity in all tropical ecosystems in many different parts of the world. In tropical rainforests there can be an average of 20-86 tree species per acre versus about four tree species in a temperate forest (Smithsonian Tropical Research Institute). The evidence that nutrients can limit growth means that we need to be better understand what controls how trees get nutrients if we are going to accurately predict how much CO2 tropical forests take in.
At the heart of my research at STRI is the idea that tree species and their associated microbial communities acquire nutrients (N and P) using different strategies. These strategies can be understood in terms of characteristics (aka traits) that we can measure such as the diameter of a root or the activity of an enzyme (phosphatase). What we will be doing is growing different tree species in native Panamanian soil in greenhouses with 800 ppm CO2 and another at 400 ppm CO2 (the control). By measuring these traits in roots and corresponding microbial activity, I hope to understand how nutrient acquisition affects the way tropical trees grow in elevated CO2.
- Mommer, L., & Hinsinger, P. (2016). Advances in the rhizosphere : stretching the interface of life. Plant and Soil. http://doi.org/10.1007/s11104-016-3040-9
- Norby, R. J., Warren, J. M., Iversen, C. M., Medlyn, B. E., & McMurtrie, R. E. (2010). CO2 enhancement of forest productivity constrained by limited nitrogen availability. Proceedings of the National Academy of Sciences of the United States of America, 107(45), 19368–73. http://doi.org/10.1073/pnas.1006463107
- Osborne, P. L. (2000). Tropical Ecosystems and Ecological Concepts. Tropical Ecology. http://doi.org/10.1017/CBO9781139057868
- Pan, Y., Birdsey, R. a., Phillips, O. L., & Jackson, R. B. (2013). The Structure, Distribution, and Biomass of the World’s Forests. Annual Review of Ecology, Evolution, and Systematics, 44(1), 593–622. http://doi.org/10.1146/annurev-ecolsys-110512-135914
- Smithsonian Tropical Research Institute. Rainforests – Diversity and Survival. February 2017 <http://www.stri.si.edu/sites/rainforest/diversity_and_survival.html>.