Bio171-F10-lec 6 - Biology 171 Monday, September 20, 2010...

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Lecture 6: Cycling of Matter & Climate Change Biology 171 Monday, September 20, 2010 Today’s Topics: Announcements This week in Discussion: Your carbon footprint Exam I: Wed. Sep. 29 Text Reading: Lecture 6: 4 th : Chapter 54 (1098-1102) 3 rd : Chapter 54 (1238-1241) Lecture 7: 4th: Chapter53 (1058-1062) 3rd: Chapter 53 (1196-1202) Productivity (end) The Water Cycle Nitrogen Cycle Carbon Cycle Greenhouse Gases Dif±cult Choices 1
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Decomposition of detritus limits the rate at which nutrients move through an ecosystem. Decomposition rate is influenced by abiotic conditions ( Figure 54.12 ) and the quality of the detritus as a nutrient source. 37
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Decomposition rate is influenced by abiotic conditions. In tropical wet forests, highly diverse decomposer communities quickly break down litter; abundant rain leaches remaining nutrients out. 38
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Primary production is the engine that drives most of the ecosystems on earth. Most primary production occurs as photosynthetic organisms (cyanobacteria, plants, algae) convert CO 2 into sugar Gross Primary Production (GPP) : The amount of light energy converted to chemical energy (organic compounds) by autotrophs in an ecosystem during a given time period (energy/area/time: grams of carbon/m 2 /year) Net Primary Production (NPP) : The gross primary production of an ecosystem minus the energy used by the producers for respiration (R) NPP = GPP - R 39
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The Earth’s Energy Budget • Net primary production is the earth’s energy budget, or “allowance” • Globally, it totals about 170 billion tons of organic carbon per year • We usually measure primary production as grams of carbon fixed per square meter per year (g C m -2 yr -1 ) • This carbon “allowance” can “buy” a lot of life 40
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Primary Productivity is Limited by: Light Intensity Temperature Precipitation Rates (terrestrial environments) Nutrient limitations, esp. Nitrogen, Phosphorous, Potassium, Iron (marine environments) 41
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Nitrogen limits plant growth (and phosphorus uptake) in this marsh 42
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Except for the world’s major deserts, terrestrial productivity declines from the equator toward the poles. Marine productivity is highest in coastal waters and lowest in the open ocean, without respect to latitude ( Figure 54.8 ). Global Patterns in Productivity 43
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NPP also varies among ecosystems by biome ( Figure 54.9 ). 44
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June Satellite Image of Global Marine Chlorophyll Concentration during Northern Hemisphere Summer Bloom ( red highest conc., purple lowest conc.; black no data). Tropical offshore waters have very low productivity due to low
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Bio171-F10-lec 6 - Biology 171 Monday, September 20, 2010...

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