Nutrient cycling

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  1. What is Nitrogen Fixation?
    Nitrogen-fixing organisms convert atmospheric nitrogen into ammonia and ammonium (forms of nitrogen that plants can utilize).

    Some are free living (soil and water), while others form symbiotic relationships with plants (Root nodules in legumes) 

    Nitrogen fixers are fungi, bacteria or cyanobacteria.
  2. What is the bacterium that lives on legumes?
  3. Steps of N fixation
    • 1- Spend nrg to break N2 bonds
    • 2- nitrogenase (enzyme in N fixers) reduces N2 to ammonia (NH3)
    • 3- N further reduced to ammonium (NH4), plants can now use
  4. What is Immobilization (N cycle)?
    Plants and microorganisms convert fixed N (inorganic) into organic compounds.

    process by which nutrients are converted from inorganic to organic forms.

    opposite of mineralization.
  5. What is Mineralization (N cycle)?
    process by which nutrients are converted from organic to inorganic forms.

     decomposition as microbes break down dead and decaying organic matter.

    opposite of immobilization.
  6. C:N ratio
    The ratio of carbon to nitrogen

    indicator of litter quality and soil fertility.

    The lower the ratio (higher proportion of nitrogen), the higher the litter quality and the more fertile the soil

    low ratio: quicker decomposition of litter (releases N quicker)
  7. what is Nitrification?
    process in the nitrogen cycle in which microorganisms convert ammonium into nitrates and nitrites.

    most commonly performed by free-living bacteria.

    Done bc it makes nitrogen more usable to broader range of plants (more soluable)
  8. What is Denitrification?
    process in the nitrogen cycle in which denitrifying bacteria convert nitrates and nitrites back into gaseous forms of nitrogen such as nitric and nitrous oxides.

    Convert what plants don't use back into gas
  9. nutrient spiraling
    an atom of a nutrient travels through a cycle, but is displaced downstream by the current as it goes. The faster the current, the more elongated the spiral.
  10. Acid Rain
    pH of 4.5 or lower

    caused by the release of acid-forming gases, primarily sulfur dioxide (SO2) and nitrous oxides (NOx).

    acidification of water habitats 

    initial harm to standing trees, effects forest nutrient cycling over time
  11. Phosphorous Cycling
    exists in sediments and mineral deposits.

    Weathering slowly releases phosphorus to terrestrial and aquatic ecosystems. Since rock weathering is a slow process, most undisturbed terrestrial ecosystems are normally phosphorus-limited.
  12. Carbon Cycling
    >99% of Earth's carbon = rocks, particularly limestone, and cycles very slowly.

    major fluxes of carbon involve less than 1% of the total. most involve CO2.
  13. Importance of phosphorus to life
    • Phosphorus is an integral part of energetics (ATP),
    • genetics (RNA and DNA) and cellular structures (cell membranes)
  14. Importance of nitrogen to living critters
    key element in amino acids, which form structural proteins and enzymes.

    forms nucleic acids and the porphyrin rings of chlorophyll and hemoglobin
  15. What are the N fixers?
    CyanoBacteria - Blue-green alga -freshwater, marine, soil

    Free-living soil bacteria

    bacteria associated w/legume roots (Rhizobium most common)

    Acinomycetes fungi associ8d with roots of some plants
  16. Denitrification facts
    occurs in anoxic environments

    N acts as electron acceptor and is reduced to N2

    May be one of primary reasons N is limiting in Marine systems
  17. What is Ammonification?
    Hydrolysis of Protein and Oxidation of amino acids produces ammonia. 

    we all do this
  18. Importance of carbon to living critters
    • found in all organic molecules including sugars,
    • proteins, nucleic acids, etc.
  19. Sources of Carbon
    atmospheric CO2

    Largest source = oceans

    Large stores in fossil fuels and carbonate rocks, but not actively cycled
  20. C Cycling
    • 1- plants bring it in w/photosynth
    •  and in aquatic systems, it readily combines with carbonate ions = calcium carbonate.(shells)

    2) plants take up about as much as is put back with respiration of plants and animals
Card Set
Nutrient cycling
Taken from SimUtext
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