OUR Ecological Footprint - 131.

13.

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? 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

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:• 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 How did sulfur get incorporated into coal? Of what consequence is its presence?

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.

***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; 8 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?”

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.

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

• 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?