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BIOL 215 Lecture Notes - Water Vapor, Heterotroph, C4 Carbon Fixation

Biology (Sci)
Course Code
BIOL 215
Neil Price

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BIOL215 Lecture 25 Notes
Nitrogen cycle is interesting to ecologists because nitrogen is a limiting resource and we've seen how
human activities have modified the natural nitrogen cycle in the plant. Human activities have altered
it in such a way to make nitrogen more available via fossil fuel, practicing agriculture, and crop
fertilizer in fixed nitrogen forms
Humans have exploited the ability to produce nitrogen as a fertilizer to enhance crop production.
Since humans add way more fertilizer then necessary, some of the nitrogen from fertilizer make their
way into waterways
One adverse effect of nutrient additions of nitrogen and phosphorous on freshwater and coastal
marine ecosystems is of oxygen depletion through addition of a limiting resource that stimulates NPP
and therefore should stimulate oxygen production but at ecosystem level, oxygen consumption
exceeds oxygen production and so you get oxygen depletion
What regulates nutrient cycling by decomposers?
One of the most important nutrient fluxes in ecosystems is the conversion of organic nutrients to
inorganic nutrients: Mineralization and it takes place during decomposition
The rate of mineralization reaction largely determines the rate at which nutrients are made
available to primary producers
The mechanical and chemical breakdown of organic matter (such as leaf litter, dead organisms,
etc. collectively known as detritus)
Forms the basis of a detrital food chain
In terrestrial ecosystems decomposition rates are affected by temperature, moisture, and
composition of the detritus and nutrients in the soil
Plant litter is primary basis of terrestrial detritus (dead organic matter) food chains: detritus broken
down more rapidly in tropical soil (right), due to high temperatures, humidity year-round
Once nutrients are released during decomposition, they are rapidly reassimilated by primary
producers thus ecosystems tend to retain nutrients - particularly nutrients that are limiting to primary
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