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BIOL215 Lecture 25 Notes.pdf

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Biology (Sci)
BIOL 215
Neil Price

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 Decomposition: • 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 reassimila
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