Ica 7 Nutrient Cycles

ICA 6 NUTRIENT CYCLES

1. What are the major macronutrients? CHONPS What are the major micronutrients? Ca, P, Fe, Mg, K, Na

2. For what are these elements (nutrients) used in organisms? CHO – organic compounds (carbos, lipids, proteins, nucleic acids) + water N, P, S – proteins (amino acids), nucleic acids Ca, P – bones, exoskeletons, cell membranes Fe, Mg – pigments, enzymes; hemoglobin (Fe); chlorophyll (Mg) K, Na – ionic balance; neural transmission Explain how physiological and ecosystem ecology are linked. Processes of all individuals’ physiology accumulate to affect entire ecosystem. Ecosystem organic pools and fluxes = sum of what element transformations occur during physiology at the individual level.

3. Figure 1. What does it mean to say “Chemicals cycle in the ecosystem”? Elements move from biotic to abiotic back to biotic pools; they are never lost, but always recyled (eventually).

4. Figure 2. (Thoroughly digest this figure…) What are the four compartments (pools) of our global ecosystem? A. Atmosphere B. Biosphere (all organisms) C. Lithosphere (soil, rock, minerals) D. Hydrosphere (water) Which elements have gaseous pools? C, N, O Which elements have sedimentary pools? P, S Why are these called ‘bio-geo-chemical ‘ cycles? (BGC) Cycles involve chemicals moving between biological and geological pools.

5. How are fluxes related to pools? A flux is the movement of elements between pools. What is the unit of a flux? amount of element moved/time/area or volume What is a sink pool? pool with input/output increasing What is a source pool? pool wth input/output decreasing In which direction between pool types does a flux occur? from source to sink pool What is residence time? pool size/flux = how long element stays in pool

6. WATER CYCLE Figure 3. A. Trace the cycle of a water molecule from a rain cloud back to a rain cloud. B. Account for the numbers on the figure; do they add up? C. What does it mean: “The water cycle is physically, not chemically, based.” Water is not chemically altered; it merely changes phases during the cycle.

7. CARBON CYCLE A. Why is this cycle closely linked to global energy flux? Carbon compounds contains chemical bond energy fixed by photosynthesis. Any transformation of carbon compounds to release energy also alters the form of carbon, results in a flux, and changes the pool in which the carbon is stored. B. What are the principal classes of processes in the C-cycle? 1. assimilation/dissimilation processes in plants/decomposers 2. exchange of CO2 between atmosphere and oceans 3. sedimentation of carbonates C. Process Inorg-Org Use/Get Energy Electron Donor/Acceptor Assimilation I to O Uses (reduction) reducer = electron donor Dissimilation O to I Gets (oxidation) oxidizer = electron acceptor

Figure 4. What is the principal assimilation process in the C-cycle? photosynthesis What is the principal dissimilation process? respiration D. What process ‘kicks in’ under anaerobic conditions? methanogenesis What is its end product? methane gas (CH4) E. What are two principal greenhouse gases generated by the C-cycle? CO2 + CH4 F. Where is the major pool of C on earth? sedimentary rock How did it get there? CO2 dissolves in water + H20  H2CO3  H+ + carbonate ions Carbonate ions + Ca2+  CaCO3 (calcium carbonate); low solubility, precipitates, and forms sediments that eventually are transformed to sedimentary rock (e.g. limestone).

G. Figure 5. What are 2 new fluxes generating more CO2 due to human activities? Fossil fuel burning and deforestation Which is greater? fossil fuel burning H. Figure 6. What 2 sink pools are being altered greatly by these activities? Atmosphere and ocean. What is meant by ‘the missing C sink’? CO2 sinks are absorbing less CO2 than are being generated by sources. Where is the excess CO2 going?

I. Figure 7. Describe the methodology of a FACE experiment. Control + treatment rings of pipes; air is blown into areas of control; CO2 blown into treatment so plants experience elevated levels of CO2 there.

Generate a hypothesis/prediction to answer the ?: Is plant productivity CO2-limited? If…plant photosynthesis + ecosystem NPP are CO2-limited, then…photosynthetic rate + NPP will be higher in areas with elevated CO2 than control areas. Figure 8. Why are there 3, not 2, treatments? The extra treatment is the same as elevated treatment (with enclosure) but at ambient levels of CO2; it controls for any effect the enclosure itself might have on plant growth. What are the results? Production was greater within enclosures + ambient CO2 than controls, but even greater when enclosure had evlated CO2. What is the conclusion? Plant productivity is CO-2 limited; plants provided extra C02 respond with greater productivity, relative to those at ambient levels. Figure 9. Qualify your conclusion. Not all dominant grasses responded to elevated CO2; the greater biomass with elevated CO2 was due to a response by only S. comata (needle grass).

Some additional mechanisms to explain: A. Needle grass under elevated CO2 was less digestible by grazers than grass under ambient CO2. What’s the ‘take-home’ message about future plant productivity and food available to cattle and other grazers? Elevated CO2 has potentially wide-ranging effects; while it may increase productivity, the plants produced may be less digestible to grazers. B. Needle grass had greater productivity because plots with elevated CO2 had more soil water. Create a scenario that accounts for the increase in soil moisture. Include: elevated CO2, accelerated CO2 assimilation, stomates, transpiration, WUE, withdrawal of water from soil Because elevated CO2 led to accelerated CO2 assimilation, plnts closed stomates at higher water potentials, thereby reducing transpiration (increasing WUE) and reducing withdrawal of water from soil.

J. Figure 10.How does the amount of atmospheric CO2 today compare to the past? Today’s levels are substantially lower than most of the past 600 million years. What caused it to drop greatly between 500 to 300 million years ago? The first forests on earth developed, thus fixing abundant C in their biomass. What caused the great increases in coal deposits in the Carboniferous? These forests were in swamping areas with anaerobic conditions causing incomplete decomposition. Sedimentation of this biomass caused conversion to coal.

Predict how the earth’s temperature changed from peak to dip in CO2. Decreased because less temperature-trapping CO2 in atmosphere. What is the concern about elevated CO2 today, given that the concentration is less than in the past. The speed with which it is happening is causing rapid temperature rise. The rate will not allow much evolutionary response; so much loss of species is expected unless migration is possible.

8. NITROGEN CYCLE Figure 11. A. Trace a N atom from the atmosphere into a plant and back to the atmosphere. What chemically happens during: Nitrogen fixation: N2  NH4 (ammonia) Nitrification x2: NH4  NO2 (nitrite)  NO3 (nitrate) Plant assimilation: NO3 organic nitrogen (e.g. amino acids, nucleic acids) Denitrification: NO3  NO2  NO  N2 Which of these processes are aerobic (A)? anaerobic (ANA)? Denitrification and N-fixation are anaerobic; all others are aerobic Which of these processes are microbial-dependent? (M) all except assimilation and ammonification.

B. Figure 12. Describe the chemical interaction between plants and N-fixing organisms. Rhizobium and blue-green algae have enzyme nitrogenase that can break triple bond of N2 and form NH4, thus providing a form of nitrogen that plants can transform into organic compounds. The plants provide the microbes with an energy source in carbohydrates.

9. PHOSPORUS CYCLE Figure 13. A. What is the dominant form of this element? phosphate Does it change chemically? No Where is the major pool? rock Why is this called a ‘geologic cycle’? Bringing P from geologic form (rock) into form that plants can absorb requires geological processes, taking geologic time (e.g. uplift of sediments; rock breakdown \ (weathering) How fast does the cycle occur? Very slowly If an atom goes from land to water, how soon will it be available to organisms on land? Geologic eons.

B. What are mycorrhizae? fungi living on/in plant roots that aid in P uptake Figure 14. Describe how they work to aid the plant. penetrate large volume of soil; secrete enzymes/acids extracellularly; increase solubility of nutrients, especially P, bring in much P for plant to use. What does the plant give to the fungus? An energy source (carbohydrates) vitamins; amino acids

C. Figure 15. What is one basic hypothesis/prediction being tested? If…plant growth is dependent on availability of phosphorus then,..plant dry weight of foliage will increase with increasing P concentration; especially when mycorhhizae are present.than when absent. Do the data support the hypothesis? Yes.

10. SULFUR CYCLE Figure 16. Figure 17. Into what compounds is the sulfate assimilated by a plant incorporated? amino acids By what process is sulfate converted to H2S, FeS? desulhydration; dissimilatory sulfur reduction Is this an aerobic or anaerobic process? anaerobic Where do we smell these products? in mucky soils; swamps; water-logged anaerobic soils and sediments How did sulfur get incorporated into coal? When non-decomposed plants got buried in swamps, allowing these anaerobic processes to proceed. Of what consequence is its presence? When we strip-mine for this coal, sulfuric acid gets into streams, When we burn high-S coal, we increase the amount of acid rain  both lower pH, lower Ca in soils, lower forest productivity. Also lower pH in lakes disrupts aquatic community.