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Unformatted text preview: The Phosphorus Cycle The phosphorus cycle is a sedimentary cycle (unlike carbon, oxygen, and nitrogen), the atmosphere is not a reservoir for phosphorous nor do microorganisms fix phosphorus as they do nitrogen. Phosphorus enters the biosphere almost entirely from the soil through absorption by plant roots. Weathering of rocks containing phosphate minerals, chiefly apatite [Ca 5 (PO 4 ) 3 OH], results in the relatively small pool of inorganic phosphorus available for organismal use. In most soils the major amount of phosphorus absorbed by plants comes from organic molecules that undergo decomposition releasing phosphorus in plant-available inorganic forms. The release of organically bound nutrients to plant-available forms is termed mineralization , a process important in the release to the soil of sulfur and nitrogen as well as phosphorus. Phosphorus is used by organisms in energy to the soil of sulfur and nitrogen as well as phosphorus....
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- Fall '08