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
***Elements and their uses in organisms
• CHO:
• N, P, S:
• Ca, P:
• Fe, Mg:
• K, Na:
• Green: focus on these cycles for macronutrients.
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
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?
• 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
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
Global BGC cycles: Water cycle: a physical model
***Start at * and trace the water cycle. How do the numbers add up?
*
Figure 3
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,• uses energy (reduction)• Reducer = electron donor
• Dissimilation processes: organic to inorganic,• gets energy (oxidation)• 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.
CO2 + H2O->H2CO3 -> H+ + carbonate ions->Carb. ions + Ca++ ->CaCO3 (calcium carbonate)
***Carbon cycle: What are 2 new fluxes due to human activities? What pools are being altered?
Figure 5
***Carbon cycle: What are 2 new fluxes due to human activities? What pools are being altered?
The missing C sink
Figure 6
ORNL FACE experiment
Figure 7
Duke FACE experiment
18 year-old forest; 6, 30-m plots; ~100 pine trees/plot; ~50 woody species; 10 years of CO2
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
G
• Generate an ‘if-then’ to answer the ?:
• “Is plant productivity CO2-limited?”
*** 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
Nitrogen cycle: N assumes many oxidation states; microbes play essential roles.
NH4 1 3b2a
2b
3a
4
5
-3
+3
i
Figure 11
Nitrogen fixation using nitrogenase (anaerobic): convert N2 to NH4
• Blue-green algae• Bacteria• e.g. Rhizobium (symbiotic with legumes)• lightning; volcanoes
Figure 12
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:• penetrate large volume of soil
• secrete enzymes/acids - increase
solubility of nutrients, especially P (N?)
• consume large amount of plant C
Figure 14
***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.
1
2 345
-2
+6
Figure 17
• 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?
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