Nutrient Cycling

***The following notes are taken directly from –Nutrient cycling and retention, Chapter 19 of  Ecology:  Concepts and Applications, 5th edition, by Manuel C. Molles Jr.***

CHAPTER 19:  NUTRIENT CYCLING & RETENTION


*Exchange of nutrients between organisms and their environment is one of the essential aspects of ecosystem function.

*Elements such as phosphorus (P), nitrogen (N), potassium (K), and iron (Fe) are used over and over again in an ecosystem.

*Nutrients are elements that are required for the development, maintenance, and reproduction of organisms.

*Nutrient cycling is the use, transformation, movement, and resue of nutrients in ecosystems.*Nutrient cycles involve the storage of chemical elements in nutrient pools, or compartments, and the flux, or transfer, of nutrients between pools.*A nutrient pool  is the amount of a particular nutrient stored in a portion, or compartment, of an ecosystem.

*Nutrient flux refers to the dynamic process by which nutrients move between pools of an ecosystem.
*A nutrient source is a portion of the biosphere where a particular nutrient is released faster than it is absorbed.*A nutrient sink is a part of hte biosphere wherea particular nutrient is absorbed faster than it is released.
PHOSPHORUS CYCLE
*”Phosphorus is slowly released to terrestrial and aquatic ecosystems through the weathering of rocks.  As phosphorus is released from mineral deposits, it is absorbed by plants and recycled within ecosystems. Mycorrhizae generally play a key role in the uptake of phosphorus in terrestrial ecosystems.  However, most phosphorus is washed into rivers and eventually finds its way to the oceans, where it will remain in dissolved form until eventually finding its way to the ocean sediments.  Ocean sediments will be eventually transformed into phosphate-bearing sedimentary rocks that through geological uplift can f
*Phosphorus is essential to the energetics, genetics, and structure of living systems.orm new land.”*Phosphorus forms part of the ATP, RNA, DNA, and phospholipid molecules.*Phosphorus is not very abundant in the biosphere, andthe phosphorus cycle does not include a substantial atmospheric pool.*The largest quantities of phosphorus occur in mineral deposits and marine sediments.

*Sedimentary rocks which are especially rich in phosphorus are mined for fertilizer and applied to agricultural soils.

THE NITROGEN CYCLE

* “Nitrogen fixing organisms break the strong bonds of the molecular nitrogen found in the atmosphere, and make it available to other organisms within the system.  Upon the death of an organism, the nitrogen in its tissues can be released by fungi and bacteria involved in the decomposition process.  The nitrogen in dead organic matter can also be used directly by mycorrhizal fungi, which can be passed on to plants.  The nitrogen in bacterial, fungal, and plant biomass.”
*Nitrogen forms part of key biomolecules such as amino acids, nucleic acids, and the porphyrin rings of chlorophyll and hemoglobin.ay pass on to populations of animal consumers or back to the pool of dead organic matter, where it will be recycled again.”*The Nitrogen cycle includes a major atmospheric pool in the form of molecular  nitrogen (N2)

*Nitrogen may exit the organic matter pool of an ecosystem through denitrification.

*Denitrification is an energy-yielding process that occurs under anaerobic conditions and converts nitrate to molecular nitrogen which moves into the atmosphere and can only reenter the organic matter pool through nitrogen fixation.

THE CARBON CYCLE*
* “Carbon moves between organisms and the atmosphere as a consequence of two reciprocal biological processes:  photosynthesis and respiration.  Photosynthesis removes CO2 from the atmosphere, while respriartion by primary producers and consumers, including decomposers, returns carbon to the atmosphere in the formof CO2.”
* In aquatic ecosystems, CO2 must first dissolve in water before being used by aquatic primary producers.  Once dissolved, carbonate may precipitate out of solution as calcium carbonate and may be buried in ocean sediments.  While some carbon cycles rapidly between organisms and the atmosphere, some remains sequestered in relatively unavailable forms (fossil fuels) for long periods of  time before returing to the atmosphere.”

*Carbon is an essential part of all organic moleculres, and, as constituents of the atmosphere, carbon compounds such ans carbon dioxide and methane substantially influence global climate.

*The massive burning of fossil fuels has increased concentrations of atmospheric CO2.

ALTERING AQUATIC AND TERRESTRIAL ECOSYSTEMS

*Eutrophication–a process where water bodies receive excess nutrients that stimulate excessive plant growth.

*Runoff containing nitrate and phosphorus rich fertilizers contributes greatly to increased nutrients in aquatic ecosystems.

*Nutrient enrichment of ecosystems, particularly with nitrogen, may be causing massive local exinctions of fungis–which results in increased primary production and reduced biodiversity.

*The loss of mycorrhizal fungi may threaten the longterm survival of entire forest ecosystems.

*The main factors affecting phosphorus concentration in lakes include geology, land use, precipitation, hydrologic budget, lake morphometry, and human population density.

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