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Bacteria are round, oval, or rod shaped single cell organisms generally about 1 micron (1/25,000 inch) in diameter. Although very small, they are abundant- often over a billion per gram of soil and a biomass of over 1 ton per acre. Bacteria immobilize nutrients in their biomass. The Carbon to Nitrogen (C:N) ratio of Bacteria is from 3:1-5:1 the lowest of any organism on the planet. There is a tremendous amount of Nitrogen stored in the biomass of bacteria as well as P, K, Ca, S, and Fe. However, these nutrients only become available when immobilized and mineralized by higher predators in the SFW.
Bacteria are divided in four groups:
Decomposers consume simple carbon compounds such as plant litter and even root exudates. They immobilize in their bodies, nutrients extracted from the organic matter. This is the first step in nutrient cycling, and is especially important in preventing nutrients from being washed away from the root zones of plants. A huge pool of Nitrogen is stored in the bacterial biomass.
Mutualists form beneficial relationships with plants. In exchange for sugars and proteins, these bacteria provide food and protection to roots. The most well known is Rhizobia. This bacterium inhabits the roots of the Pea family (legumes) and fixes nitrogen (N2) from the atmosphere into ammonium (NH4) an available form for the plant. It is thought that up to a third of all plant available nitrogen is the result of the action of Rhizobia.
Pathogens are opportunists that depend on points of weakness in the SFW and plants. They have evolved to generally operate best in reduced oxygen environments; this is because the aerobic organisms that compete or consume the pathogens are unable to adequately function. Where there are voids in the interaction of beneficial organisms in the soil, and on plants, pathogens may find food and habitat. Where there is normal, healthy food web, pathogens are either consumed, or the competition for food and habitat is too great for survival.
Lithotrophs obtain their energy from nitrogen, sulfur, iron, or hydrogen instead of Carbon. They are responsible for the liberation of many crucial nutrients in the parent bedrock, and participate in the formation of soil. Lithotrophs play a crucial role in the maintenance of life on Earth. These bacteria are also able to decompose toxic materials in the soil.
Bacteria Links: http://en.wikipedia.org/wiki/Bacteria
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