Transcript 26 Nutrient Cycles 2009

OUR Ecological Footprint - 13
1.
13.
Pathways of Elements in the Ecosystem:
Bio-geo-chemical (Nutrient) Cycles
Objectives:
• 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
***Elements and their uses in organisms
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CHO:
N, P, S:
Ca, P:
Fe, Mg:
K, Na:
• Green: focus on these cycles for
macronutrients.
Nutrients and their uses in organisms
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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
The fate of matter in ecosystems:
Energy flows through the system once.
Chemicals (nutrients) cycle = reused.
Figure 1
Ecosystems can be large or small. Ecosystem
boundaries can be arbitrary, but must be
defined.
Can be large spatial and temporal scales.
***What are the four compartments of
the global ecosystem?
For C, identify 4 natural processes
that contribute to flux.
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Atmosphere (air)
Biosphere (all organisms)
Lithosphere (soil, rock, minerals)
Hydrosphere (water)
• Hence: bio-geo-chemical cycles
Ecosystems modeled as linked
compartments (box = pool; arrow = flux).
Figure 2
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
Human alterations affect cycles:
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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
Global BGC cycles: Water cycle: a physical
model
*
Figure 3
How did sulfur get incorporated into coal?
Of what consequence is its presence?
***Start at * and trace the water cycle.
How do the numbers add up?
Figure 3
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
Classes of chemical transformations:
• Assimilation processes: inorganic to organic,
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uses energy (reduction)
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Reducer = electron donor
• Dissimilation processes: organic to inorganic,
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gets energy (oxidation)
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Oxidizer = electron acceptor
Redox reactions
Transformations of compounds in
the carbon cycle.
(GH gas)
Microbes
(GH gas)
Figure 4
Most of the earth’s C is in sedimentary
rock as precipitated calcium carbonate.
***Carbon cycle: What are 2 new fluxes due to
human activities? What pools are being
altered?
Figure 5
Figure 6
***Carbon cycle: What are 2 new fluxes due to
human activities? What pools are being
altered?
The missing C sink
ORNL FACE experiment
Figure 7
Duke FACE experiment
18 year-old forest; 6, 30-m plots;
~100 pine trees/plot; ~50 woody
species; 8 years of CO2
Carbon budget for pine and sweetgum forests
exposed to elevated carbon dioxide
Units: gC m-2 y-1; Open bubbles, ambient plots; closed
bubbles, fumigated plots. E. DeLucia, unpub.
G
• Generate an ‘if-then’ to answer the ?:
• “Is plant productivity CO2-limited?”
The C-cycle in a semi-arid grassland. How
will rising CO2 affect its productivity?
Why are there 3, not 2, treatments?
What is the conclusion?
Figure 8
Do all species respond similarly to elevated
CO2? Qualify the earlier results.
Figure 9
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
*** What caused the large drop in CO2?
Predict what happened to earth’s temperature
from the peak to the dip in CO2.
Figure 10
Carboniferous forest: a huge sink for C
Fossil soils reveal changes in the biosphere.
Nitrogen cycle: N assumes many
oxidation states; microbes play essential
roles.
4
-3
NH4
3a
1
3b
2a
2b
i
5
+3
Figure 11
Nitrogen fixation using nitrogenase
(anaerobic): convert N2 to NH4
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Figure 12
Blue-green algae
Bacteria
e.g. Rhizobium (symbiotic with legumes)
lightning; volcanoes
Many legumes are N-limited unless
infected by Rhizobium.
Phosphorus cycle includes few chemical changes of
PO4-3. Solubility less with low + high pH. Losses to
sediments.***What are consequences?
Figure 13
Mycorrhizae: symbiosis
(mutualism) of fungi/plant roots
How mycorrhizae work:
Figure 14
• penetrate large volume of soil
• secrete enzymes/acids - increase
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solubility of nutrients, especially P
• consume large amount of plant C
***What is one basic
hypothesis/prediction being tested?
Do the data support the prediction?
Figure 15
Sulfur cycle: used in 2 amino acids
Sulfur exists in many oxidized and
reduced forms; many microbes.
-2
2
5
4
3
1
+6
Figure 17
How did S get incorporated into coal?
• 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.