OUR Ecological Footprint - 13 1. 13.. Pathways of Elements in the Ecosystem: Bio-geo-chemical...
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Transcript of OUR Ecological Footprint - 13 1. 13.. Pathways of Elements in the Ecosystem: Bio-geo-chemical...
![Page 1: OUR Ecological Footprint - 13 1. 13.. Pathways of Elements in the Ecosystem: Bio-geo-chemical (Nutrient) Cycles Objectives: Elements and their uses Spatial.](https://reader036.fdocuments.net/reader036/viewer/2022062408/56649f1f5503460f94c37a4d/html5/thumbnails/1.jpg)
OUR Ecological Footprint - 131.
13.
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Pathways of Elements in the Ecosystem: Bio-geo-chemical (Nutrient) CyclesObjectives:
• Elements and their uses
• Spatial and temporal scales of ecosystems
• General model of cycles in ecosystems
• H2O, C, N, P, S cycles
• Sources, sinks, pools
• Chemical changes
• Microbes involved
• Human changes
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***Elements and their uses in organisms
• CHO:
• N, P, S:
• Ca, P:
• Fe, Mg:
• K, Na:
• Green: focus on these cycles for macronutrients.
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Nutrients and their uses in organisms• CHO - organic compounds and water• N, P, S - proteins, nucleic acids• Ca, P - bones, exoskeletons, cell membranes• Fe, Mg - pigments, enzymes - hemoglobin, chlorophyll• K, Na - ionic balance, neural transmission
• Physiological ecology and ecosystem ecology linked
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The fate of matter in ecosystems:Energy flows through the system once.Chemicals (nutrients) cycle = reused.
Figure 1
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Ecosystems can be large or small. Ecosystem boundaries can be arbitrary, but must be defined.Can be large spatial and temporal scales.
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***What are the four compartments of
the global ecosystem? For C, identify 4 natural processes that contribute to flux.
• Atmosphere (air)
• Biosphere (all organisms)
• Lithosphere (soil, rock, minerals)
• Hydrosphere (water)
• Hence: bio-geo-chemical cycles
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Ecosystems modeled as linked compartments (box = pool; arrow = flux).
Figure 2
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What is measured in a nutrient cycle?
• Pool: compartment (box);• (storage reservoir)
gaseous (C, N, O) sedimentary (P, S, C)• Flux: amount / time / area or volume of movement between compartments (arrow)
• Sink: pool with input/output increasing• Source: pool with input/output decreasing• Residence time = pool size/flux
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Human alterations affect cycles:• size of pools, sources and sinks
• rates of flux
• residence time
• disturbances cause nutrients loss from one
• ecosystem pool and gain in another
• introduced species, e.g. N-fixing species
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Global BGC cycles: Water cycle: a physical model
***Start at * and trace the water cycle. How do the numbers add up?
*
Figure 3 How did sulfur get incorporated into coal? Of what consequence is its presence?
Figure 3
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Carbon cycle
• closely tied to global energy flux • solar-powered
• principal classes of C-cycling processes: 1) assimilation/dissimilation processes in plants/decomposers
2) exchange of CO2 between air and oceans 3) sedimentation of carbonates
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Classes of chemical transformations:
• Assimilation processes: inorganic to organic,• uses energy (reduction)• Reducer = electron donor
• Dissimilation processes: organic to inorganic,• gets energy (oxidation)• Oxidizer = electron acceptor
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Redox reactions
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Transformations of compounds in the carbon cycle.
(GH gas)
Microbes
(GH gas)
Figure 4
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Most of the earth’s C is in sedimentary rock as precipitated calcium carbonate.
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***Carbon cycle: What are 2 new fluxes due to human activities? What pools are being altered?
Figure 5
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***Carbon cycle: What are 2 new fluxes due to human activities? What pools are being altered?
The missing C sink
Figure 6
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ORNL FACE experiment
Figure 7
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Duke FACE experiment
18 year-old forest; 6, 30-m plots; ~100 pine trees/plot; ~50 woody species; 8 years of CO2
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Units: gC m-2 y-1; Open bubbles, ambient plots; closed bubbles, fumigated plots. E. DeLucia, unpub.
Carbon budget for pine and sweetgum forestsexposed to elevated carbon dioxide
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G
• Generate an ‘if-then’ to answer the ?:
• “Is plant productivity CO2-limited?”
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The C-cycle in a semi-arid grassland. How will rising CO2 affect its productivity?
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Why are there 3, not 2, treatments?What is the conclusion?
Figure 8
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Do all species respond similarly to elevated CO2? Qualify the earlier results.
Figure 9
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Additional mechanisms that arise with elevated CO2…• Needle grass under elevated CO2 was less digestible by
grazers than under ambient CO2. • What’s the ‘take-home’ message about future plant
productivity and food available to cattle and other
grazers?
• Needle grass had greater productivity. Why?• Plots with elevated CO2 had more soil water. • Create a scenario that accounts for the increase in soil
moisture.• Include: acclerated CO2 assimilation, stomates,
transpiration, WUE, withdrawal of water from soil
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*** What caused the large drop in CO2?Predict what happened to earth’s temperature
from the peak to the dip in CO2.
Figure 10
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Carboniferous forest: a huge sink for C
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Fossil soils reveal changes in the biosphere.
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Nitrogen cycle: N assumes many oxidation states; microbes play essential roles.
NH4 1 3b2a
2b
3a
4
5
-3
+3
i
Figure 11
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Nitrogen fixation using nitrogenase (anaerobic): convert N2 to NH4
• Blue-green algae• Bacteria• e.g. Rhizobium (symbiotic with legumes)• lightning; volcanoes
Figure 12
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Many legumes are N-limited unless infected by Rhizobium.
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Phosphorus cycle includes few chemical changes of PO4
-3. Solubility less with low + high pH. Losses to sediments.***What are consequences?
Figure 13
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Mycorrhizae: symbiosis (mutualism) of fungi/plant roots
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How mycorrhizae work:• penetrate large volume of soil
• secrete enzymes/acids - increase
• solubility of nutrients, especially P
• consume large amount of plant C
Figure 14
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***What is one basic hypothesis/prediction being tested?Do the data support the prediction?
Figure 15
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Sulfur cycle: used in 2 amino acids
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Sulfur exists in many oxidized and reduced forms; many microbes.
1
2 345
-2
+6
Figure 17
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• When non-decomposed plants got buried in swamps, allowing these anaerobic processes to proceed.
Of what consequence is its presence?
• strip-mine - sulfuric acid into streams. • burn high-S coal, increase acid rain --> both lower Ca in soils, lower forest productivity.
Also lower pH in lakes disrupts aquatic community.
How did S get incorporated into coal?