soilmiddle

SOIL ORGANISMS
(Middle School Level)
by Mrs. Eilisha Joy Bryson

What is soil, and what are all of the organisms that live in it? What do they do in the soil?
Sometimes people call soil dirt, but that may lead you to believe that it should be swept-up and thrown away, as if it is not valuable. In fact, soil is very complex and very valuable and there are many reasons why.

Have you ever dug-up the soil in your yard or garden or in the woods? Maybe you never did because you didn't want to get creeped out from all of the bugs. How many different types of bugs can you recall?????? Well, there are literally billions of organisms that live within the soil. They are often grouped into two major categories, microorganisms and macro fauna. Microscopes are needed to see the microorganisms, and macro fauna are the larger organisms that you can see with the naked eye. Even those are small though. (There are also mega fauna, which include larger animals like tigers, elephants, but they won't be included in this discussion.)

The first thing we will look at are the microorganisms that live in the soil, and what they do in the soil. Again, they are mainly too tiny to see without the aid of a microscope, but they hold a great importance to the soil and to other organisms around them. Pictures are included.
After that, the larger soil dwellers, the macro fauna, will be described. These are the little bugs that may scare you, but don't be too quick to try to kill them off. They are equally important to the soil and to larger animals as well, including you and me! Pictures are included.
Finally, there is a food web shown so that you can see how these organisms are all connected and dependent on each other. Humans are not shown, but we fit into this food web too!

Micro-Organisms
Bacillus http://biochem.ultraevil.com/bio/ Images/bioloskoorozje/ anthrax/BacillusAnthrax.jpg	Bacteria are organisms that have only one cell and are therefore microscopic. But don't let their size fool you! There are anywhere from 100 MILLION to 1BILLION bacteria in just 1TEASPOON of soil!!!! They are decomposers, eating dead plant material and organisms' waste. By doing this, the bacteria release nutrients that other organisms could not access. The bacteria do this by changing the nutrients into a form that can be used. Do you know what soil smells like? Well actinomycetes, a unique type of bacteria, cause that smell, and it is a good sign of healthy soil. Actually, people have been smelling soil for many, many years as a way to judge if the land is good for planting.	Actinomycetes http://www.blm.gov/nstc/soil/bacteria/ Actinomycetes http://soils.usda.gov/sqi/concepts/ soil_biology/images/SSSA14_LR.jpg
http://www.emlab.com/app/fungi/ Fungi.po?event=fungi&type= primary&species=12&name=Chaetomium Mycorrizae http://bio1100.nicerweb.com/ doc/class/bio1100/Locked/ media/ch28/mycorrhizal.jpg	Fungi are organisms. They are not plants, nor are they animals. They group themselves into strings called hyphae. The hyphae then form groups called mycelium. They are less than an inch wide but can get as long as several meters. They are helpful but could also be harmful to soil organisms. Fungi are helpful because they have the ability to break down nutrients that other organisms cannot. Fungi release them into the soil, and other organisms get to use them. Fungi can attch themselves to plant roots. Most plants grow much better when this happens. This is a good relationship called mycorriza. The fungi help the plant by giving it those needed nutrients, and the fungi get food from the plant, the same food that plants give to humans. On the other hand, fungi can get food by being parasites, attaching themselves to plants or other organisms, but for selfish reasons. There are beautiful mushrooms, shown below. This is only one part of the fungus; its mycelium are growing underground. The mushrooms form when the fungus is trying to reproduce. Mushroom Click here for more information on fungi. Click here for more information on mycorrhizae.	Mushrooms http://www.namyco.org/photography/ MWood/index.html
Testate amoebae http://purgatorio1.com/ wp-content/nov05/41g.jpg Naked amoebae http://purgatorio1.com/wp-content/ nov05/41e.jpg	Protozoa are organisms that have only one cell, and are microscopic, but larger than bacteria. They behave like animals in how they move, but they are not animals. They are a type of simple organism. There can be millions found in a square meter of soil. They are grouped by the ways they move: amoebae use a psuedo (fake) foot, ciliates have cilia (short hair) and move them very fast, and flagellates have one or more flagella (whips) and move them very fast. Protozoa eat bacteria which actually helps keep the bacteria population growing. Protozoa help other soil organisms and plants by releasing a usable form of nitrogen into the soil. These other organisms and plants cannot do this by themselves. Testate amoebae (oval) with bacteria (beside amoebae) and clay (largest) http://soils.usda.gov/sqi/concepts/soil_biology/protozoa.html	Ciliate http://research.plattsburgh.edu/ Ciliates/images/144small.jpg Flagella http://www.blm.gov/nstc/soil/protozoa/ images/flagellate.jpg
Macro Fauna
http://www.simplyhydroponics.com/ predator_nematods.htm	Nematodes are worms that do not have any segments in their body. You may have seen these before, but there are actually 22,000 differnt species of nematods. There are LOTS of them living in the soil, about 10 to 20 MILLION in a square meter! They are small, microscopic even, but they can grow up to a meter long. Nematodes can be helpful and sometimes can become pests in the soil. They eat plants, fungi, and bacteria. This can be good or bad. It is good because when the small nematods eat bacteria and fungi, they release some of the bacteria's and fungi's good nutrients into the soil. When there are too many nematodes they can over-eat and will throw-off the natural balance of the bacteria's and fungi's population. Predatory nematodes help with this by eating some of the smaller nematodes. Although it sounds strange, this keeps the populations in check.	Nematode http://en.wikipedia.org/ wiki/Nematoda
Arthropods are bugs that have jointed (arthro) legs (pods) and an exoskeleton. They include insects, mites, spiders, ants, termites, beetles, cockroaches, all the bugs that creep many of us out! There are over a MILLION different species.They can be microscopic to several inches long. In a square meter, there could be 500 to 200,000 arthropds (not close to the number of nematods). Some arthropds feed on plants (herbivores), some on dead plants (decomposers), some on other animals (carnivores), some on fungi and bacteria. The more the fungi and bacteria are eaten, the more they continue to grow. It is a strange idea, but it is true. They release nutrients from the bacteria and fungi into the soil and air. Without them, other organisms would not have acccess to the nutrients. They help bacteria get around in the soil by transporting them on their exoskeletons. They also feed the bacteria and fungi when they give off waste. Click to learn more about these insects: caddisflies butterflies dragonflies	Difference between millipedes and centipedes http://mkat.iwf.de/mms/images/ 02000018210220000000_hi.jpg	Ant http://www.foogle.biz/ants/ ants_Pseudomyrmex_apache.jpg Plant mite http://www.sel.barc.usda.gov/acari/ frames/plantfeed.html Wiremorm http://mint.ippc.orst.edu/ symphadult_lg.htm
Slug http://www.samford.edu/schools/artsci/ biology/zoology/invertzoo-05	Mullusks include slimy snails and slugs, and many shellfish. There are over 100,000 species. Many, obviously live in water environments, but they are special in the soil because they are able to digest a material in plants, cellulose, that most other organisms cannot. Therefore, they eat living and dead plants. Did you know that sea snails provide the seashells that wash-up at the beach. Those shells then become the homes of hermit crabs, who live in several seashells throughout their lives. Snails only use one shell for their entire lives. They just keep adding more chitin to make it bigger. When they roll into their shell they give-off material that creates a door so no predators can get in.	Snail http://webpages.charter.net/teefile/ biognomen/Mollusca.html
Earthworm burrowing http://pt.wikipedia.org/wiki/ Imagem:Suelos136.jpg	Oligochaeta are segmented worms. There are about 7000 species of eathworms, which can be anywhere from 1 inch to about 2 meters long. Imagine seeing a worm that long! In a square meter, there could be anywhere from 50 to 500 worms depending on the climate. If there are earthworms in your garden, then you are in luck! We discussed why it is good for soil organisms to eat bacteria and fungi, and earthworms feed on them too. Earthworms mainly help the soil when they burrow through it. While doing this, they create tunnels. Other organisms use that space to travel, making it easier for them to get around and do their business. These tunnels also give the rain somewhere to go, which gives the plants' roots more access to the water. While burrowing, the earthworms steadily eat and process soil and dead plant material. They release their waste throughout the soil, but it is so rich with nutrients and bacteria that their waste is like a fertilzer. Actually, you can buy wormcasts form plant stores to put into your own garden! Click here to learn: fun facts about earthworms how earthworms breathe	Enchytraeids http://mkat.iwf.de/mms/images/ 02000018210220000000_hi.jpg

Soil Food Web
The following diagram shows how all of the organisms that are discussed above are dependent on each other for survival. Even though some of them are microscopic, they still need food, even plants. This is called a food web. Can you figure out where the humans would fit into this food web? What do humans eat in order to survive? Don't forget that people from other parts of the world may eat different things that you don't eat!

http://soils.usda.gov/sqi/concepts/soil_biology/sbclipart.html
foodweb

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Last Updated August 21, 2006