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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