Tropical Rainforest

From MicrobeWiki, the student-edited microbiology resource

Introduction

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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

Describe the physical and chemical characteristics of the environment, using as many sections/subsections as you require. Look at other topics available in MicrobeWiki. Which involve processes similar to yours? Create links where relevant.

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 20o - 30o C (68o - 86o F). Annual temperature flux is pretty low, usually not higher than 4 degrees. The humidity is also extremely high, with dew points being between 15oC - 20oC (59oF- 68oF), 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

What kind of microbes do we typically find in this environment? Or associated with important processes in this environment? Describe key groups of microbes that we find in this environment, and any special adaptations they may have evolved to survive in this environment. Add sections/subsections as needed. Look at other microbe listings in MicrobeWiki. Are some of the groups of microbes from your environment already described? Create links to those pages. Specific microbial populations will be included in the next section.

Subsection 1

Subsection 1a

Subsection 1b

Subsection 2

Examples of organisms within the group

List examples of specific microbes that represent key groups or are associated with important processes found in this environment. Link to other MicrobeWiki pages where possible.

Current Research

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References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

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