Tropical Rainforest

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The tropical rainforest is a biome located across the earth on land on and around the equator. It has the highest biodiversity of all the earth's ecosystems, both in flora and fauna as well as microbes. This high diversity is due to the optimal growing conditions at equatorial locations: Abundant rainfall and warm temperatures, as well as intense sunlight. There is no seasonality in the rainforest(meaning it is evergreen) so the native flora have evolved their own flowering and fruiting seasons. Although sunlight is intense, the lower levels of the rainforest are highly lacking in it due to the thick canopy layer blocking out the sky. As a result, forest floor conditions are dark and moist, which is the optimum condition for decomposition. Nutrient cycling is extremely vital in the rainforest, and because microbes drive nutrient cycling, they are key to sustaining this ecosystem. The huge biodiversity of bacteria and fungi in the rainforest is not due to nutrient rich soils. In fact, the rainforest's soils are quite nutrient poor. What powers the recycling in this ecosystem is the constant thick layer of leaf litter atop the forest floor. This is where the decomposition occurs, and is the home for a wide range of microorganisms like bacteria, fungi, and even protozoa in all different shapes and sizes.

Physical environment

Physical Characteristics

As mentioned above, the rainforest is at an optimum location for growth in terms of physical characteristics. The sunlight is direct at the equator and more intense than anywhere else on the planet. Not only is this great for photosynthesis, but it also keeps the climate at a steady high temperature all year round (between 20°C - 30°C (68° - 86°F). Annual temperature flux is pretty low, usually not higher than 4 degrees. The humidity is also extremely high, with dew points being between 15°C - 20°C (59°F- 68°F), making the high temperatures even more oppressive and sticky. There is no dormant period due to the lack of seasonality, and the trees are green year round. As aforementioned, this provides for a constant source of carbon for the microbes working to decompose. Precipitation often exceeds 100 inches per year, so there is always plenty of excess water to keep the soil and pretty much everything else damp or simply moist.

Chemical Characteristics

Most of the world’s rainforests grow on red, clayey soils called laterite. Laterite is poor in nutrients and acidic. Tropical forests are old growth forests, and tend to be at areas of lower elevations (such as the Amazon baisin). These locations have little or no volcanic activity that would bring up new nutrients from the earth’s crust. Because of this, rainforest soils are very weathered of minerals that come from rock, such as K, Ca, P, and Mg. What they are rich in is metal oxides like aluminum and iron due to the lateralization process, giving rainforest soils the red and yellow colored oxisol they are known for.

Biological interactions

The overwhelming majority of carbon and nutrients is in the vegetation and dead wood of the rainforest, not the soils. Organic matter decay occurs so rapidly in the litter of the forest floor that barely any nutrients reach the soil. This leaves the soil practically sterile. While it may seem strange that sterile soils create the most lush vegetation on earth, the key to the extensive foliage is the microorganisms that dominate the forest floor, constantly working to recycle nutrients for new growth, whether it be through the leaf litter, dead and rotting wood, animal feces, etc.

Anthropological Issues with Rainforest Soil

From early on, people have had issues interacting with rainforest soil. Settlers didn’t realize how different this ecosystem was from the temperate forests they were used to, in which all the nutrients were within the soil. Much of the rainforest was cleared due to this misconception. When crops were planted in attempts at agriculture in these tropical climates, the people were at a loss when they died. Sadly, while we know better today, rainforest is still deforested and degraded at an alarming rate. Profits on goods such as wood, exotic species and other things are still enough incentive for companies to continue taking what they want of the ecosystem far beyond a sustainable level. Slash and burn agriculture is also an issue because much of the rainforest lies in third world countries, where people are simply trying to survive and using any resources they have.

Microbial processes

Microbial processes occur at a tremendous scale. There is a great abundance of different decomposers present on the forest floor, including bacteria, fungi, and even termites. Organisms such as these take up nutrients in the organic matter lying on the forest floor (leaves, wood, dung, carcasses, etc). In the most productive areas, it is simply a matter of minutes before a pile of dung is found and used by different insect species. Insects use feces not only as an energy source but also for the calcium salts present. When vegetation dies, it is broken down and taken up by other living plants quite quickly. This process is aided by mycorrhizae fungi, which form a mutualistic bond with the plant. Mycorrhizae attach to plant roots and help uptake nutrients more efficiently and from a wider spectrum. The plants provide the fungi with sugars and starch they have produced in return for this service, so both organisms benefit. It is also thought that mycorrhizae may aid in resistance to disease and/or drought.

Key Microorganisms

There are more types of microorganisms found in the tropical rainforest then we know or have come close to studying. As an advancing scientific and technological community, we have much to learn in terms of this subject. Some types of microorganisms that we know are found in the rainforest are:

Acidophilic bacteria

High amounts of water moving through the soil make it acidic, so acidophiles would prefer this environment


Very diverse and prevalent: Their role has been studied but still so much remains in understainding these complex bacteria. Their ecological value as an antimicrobial compound creater makes them quite important to the forest, and a potential light to future biotechnology.


Very diverse and prevalent:They function as a benefactor to plants by attaching to roots and assisting in the efficiency of nutrient uptake, as well as expanding the rhizosphere.


Very diverse and prevalent, along with countless other saprophytic flowering plants. Function primarily as nutrient cyclers through the process of decomposition. Rainforest fungal species are well adapted for fast, efficient decomposition.


Little is known due to lack of research, but thought to be very diverse and beneficial in stimulating bacterial activity and nutrient cycling

Examples of organisms within the group

Actinomycetes: Streptomyces, Micromonospora, Actinoplanes, Actinomadura, Nonomuria, Nocardia and Streptosporangium, etc.

Protists: Foraminifera, etc. (more data needed)

Mycorrhizal fungi

Bluegreen algae (cyanobacteria) – grow under cuticle of tropical leaves

Current Research

(At right)Scanning electron microscope photo of Gliocladium roseum - in red

Diesel fungi.jpg Even though the rainforest has the highest microbial diversity of any biome on earth, we know very little about it. Because it is under great threat, University of Massachusetts Amherst microbiologist Klaus Nusslein has undertaken a microbial observatory project in order to catalog the microorganisms of the tropics and study effects of agricultural practices in Brazil. The observatory will target three habitats: pristine rainforest, burned and cleared grazing areas, and secondary growth rainforest. A unique and valuable fungus had been discovered living on the trees of the tropical rainforest in South America. This fungus, called Gliocladium roseum, can make diesel compounds, and is the only organism known that produces compounds so close to fuel. It could potentially be an entire source of biofuel. Microbiologist Kristen DeAngelis has started a venture in advancing biofuel for future sustainability. Funded by the U.S. Department of Energy Joint BIoEnergy Institute (JBEI), she leads a group of scientists in searching tropical microbial communities for especially potent deconstructive enzymes. She was struck with the idea after witnessing how quickly a tropical storm’s debris was decomposed on the forest floor. This work is key to JBEI’s mission in advancing the next generation of biofuel: Liquid fuels derived from the solar energy stored in plant biomass.


Ahlberg, Pam, ed. “Amazon Rainforest Observatory to Catalog, Study Soils.” University of Massachusetts Amherst. Lab Manager Magazine. 16 July 2009. <>.

Bamforth, Stuart S. 2007.“Protozoa from aboveground and ground soils of a tropical rainforest in Puerto Rico.” Pedobiologia. Vol. 50(6) 515-525.

Bentley, Barbara L. 1987. “Nitrogen fixation by Epiphylls in a tropical rainforest.” Annals of the Missouri Botanical Garden. Vol 74(2) 234-241.

Krotz, Dan. “Rainforest holds clues for more efficient biofuel production.” Lawrence Berekely National Laboratory News Center. 22 April 2009. <>.

Michael E. The Physical Environment: an Introduction to Physical Geography. 2006. 11 April 2010. <>.

Milton, Ysabel, and Michael Kaspari. “Bottom-up and top-down regulation of decomposition in a tropical forest.” Oecologia. 2007. Vol. 153: 163-172.

“Rainforest fungus makes diesel.” Science News. 3 November 2008. <>.

Strobel, Gary A. 2002. “Rainforest endophytes and bioactive products.” Critical Reviews of Biotechnology. Vol. 22(4) 315-333.

“Tropical Broadleaf Evergreen Forest: The Rainforest.” Radford University. 1997. <>.

Wang, Y, et al. September 1999 “Investigation of actinomycete diversity in the tropical rainforests of Singapore.” Journal of Industrial Microbiology and Biotechnology. Vol. 23(3) 178-187.

Edited by student of Angela Kent at the University of Illinois at Urbana-Champaign.