Download LECTURE 22 CH 7 PATHWAYS OF ELEMENTS IN

LECTURE 26 CH 23
PATHWAYS OF ELEMENTS IN THE ECOSYSTEM
MAJOR CONCEPTS
1. Energy transformation and element cycling are intimately linked.
2. A model of ecosystems includes linked compartments (pools):
air; organisms; soil/rock; water
3. Nutrients move from source compartments to sink compartments;
the rate of movement = flux
4. The water cycle is physical, not chemical.
5. The carbon cycle is closely tied to the flux of energy through the biosphere.
6. Nitrogen exists in many oxidized and reduced forms in its cycling.
7. The phosphorous cycle involves little change in chemistry; a very large pool
in rock; P is ‘lost’ to inactive sediments in oceans/lakes; its cycle is geological
in time scale.
8. Sulfur exists in many oxidized and reduced forms in its cycling.
9. C, N, and S cycles differ greatly under aerobic vs. anaerobic conditions.
10. Microorganisms assume significant and diverse roles in N, P, S cycles.
Elements and their uses in organisms
CHO: organic compounds and water
N, P, S: proteins, amino acids
Ca, P: bones, exoskeleton, cell membranes
Fe, Mg: pigments, enzymes (e.g. hemoglobin, chlorophyll
K, Na: ionic balance, neural transmission
Matter cycles/is reused; energy flows; not reused
Energy transformations and element cycling are intimately linked 23.1, 23.2
Features of ecosystems
Size; boundaries
Temporal scale
General model of ecosystems 23.3
Linked compartments (boxes) (pools) (air; organisms; soil/rock; water)
Rate of movement between compartments (arrows) (fluxes)
Sinks: boxes with input/output increasing
Sources: boxes with input/output decreasing
Residence time varies among pools and cycles
Water cycle 23.4
Physical model, not chemical
Balance of fluxes
Carbon cycle 23.5
Tied to energy flux; solar-powered
Processes 23.6
Assimilation; dissimilation; redox reactions
Photosynthesis, respiration, methanogenesis
Exchange of CO2 between air and oceans
Sedimentation of carbonates 23.7
Human alterations: fossil fuel burning; tropical deforestation as new fluxes
The “missing sink”: sources>sinks
Elevated CO2 experiments: Are plants limited by [Co2]? pg.493; Fig. 2, 3
Can plants sequester more carbon? Does increased CO2 act as fertilizer?
Geological time scale changes in cycle 23.9, 23.10
Variation in flux and pools among biomes
Nitrogen cycle 23.11
Many oxidized/reduced forms
Importance of microbes
Nitrogen fixation 23.12
Nitrification
Denitrification
Phosphorus cycle 23.14
Little change in chemistry; form = (PO4-3)
Large lithosphere pool; no atmospheric pool
Lost to inactive sediments in oceans/lakes
Cycle is geological in time scale
Importance of mycorrhizae in phosphorus uptake
Sulfur cycle 23.17
Many oxidized/reduced forms
Importance of microbes
Microorganisms assume diverse roles in element cycles
Summary: 1-12, 14, 16-17