nitrogen - Converted

SQ questions:

1. According to Pastor & Post 1988, " the carbon & nitrogen cycles are strongly and reciprocally linked." Discuss the linkages.
2. Norby and colleagues grew tulip poplar trees for 3 years at 3 levels of CO2 enrichment. Photosynthetic rate nearly doubled at high CO2 levels, but there was no difference found in aboveground biomass of trees grown at normal or elevated CO2 levels after 3 years.How is this possible?
3. Compare a gaseous vs a non-gaseous cycle ( for example nitrogen vs. phosphorus). What difference does it make that a cycle involves a gaseous component ( or not) in terms of cycling rate, availability in the environment and to organisms, enegetics involved? what is more limiting to organimal growth.. nitrogen or phosphorous and explain in terms of the question. If you think of stability: resistance vs resiliene.. how would this concept fit in with the cycling of the two elements?
4. How does the surrounding environment impact on the cycling of an element.. choose one and explain how pH, temp or whatever parameters would affect it avalibility.
5. This is a theoretical question.. if nitrogen forms are related to energy or energetics and energetics according to West dictates size and age of organisms, can there be a 1/4 or something akin law for nitrogen use in bodies? explain using his theory..
6. Know the stages of the nitrogen cycle, who is involved.

Biogeochemical cycling:

Biogeochemical cycles are quite complex, involving interactions not only between the abiotic compartments but also between the biotic players themselves and interactions between the biotic and abiotic components.

The rates of exchange between the sinks of atoms and molecules are critical to ecosystem functioning, as well as the energy exchanges between the biotic and abiotic compartments. In the diagram below note some of the critical physical donor and recipient compartments: the oceans, the atmosphere, the rocks/sediments and the soil. Exchanges between the biotic compartments ( living as well as fossilized animal and plants) and these physical compartments are generally though not always swifter than between the physical stocks.

Sink
Amount in Billions of Metric Tons
Atmosphere ---------------------------------------------------->578 (as of 1700) - 766 (as of 1999)
Soil Organic Matter--------------------------------------------> 1500 to 1600
Ocean --------------------------------------------------------------->38,000 to 40,000
Marine Sediments and Sedimentary Rocks ----------->66,000,000 to 100,000,000
Terrestrial Plants ---------------------------------------------->540 to 610
Fossil Fuel Deposits -------------------------------------------->4000

Gaseous cycles:

Carbon cycle: First let's review the carbon cycle shown below and decide which are the rate limiting flows ( where the carbon is tied up) and where the fastest transfer flows occur.

The 3 primary carbon flows are in:

a.Carbon exchange involved in photosynthesis and respiration

b.Exchange between oceans, lakes & aquatic bodies and the atmosphere:

CO2 + H₂O <---> H₂CO₃

H2CO3 <--> H⁺ HCO3^-<--> 2 H⁺ + CO3 ^2-

Notice how this is a pH dependent rx; if too acidic what will happen? According to this ENN article, pH effects may have major ramifications

For the last 50 years, scientists may have been leaving out a key element in their research of world climate change. New University of California, Davis research The Spero group suggest that fluctuations in the acid-base balance of the ocean may be this missing importance of link. "If the changes that we see in the fossil record were due to changes in the ocean's pH, it means we'll have to take a hard look at the ocean's carbon-buffering system as a controller of greenhouse gases," says lead researcher Howard Spero, an associate professor of geology. "It will reinforce the notion that oceanic processes drive climate."

c.The precipitation and dissolution between the carbonate rocks ( limestone & dolomite)

Ca²⁺ + CO₃²- <---> CaCO₃

Why is the ocean so critical in terms of carbon cycling? is it possible that the ocean's ability to tie up carbon in the form of carbonates may slow down? how much CO2 is in the ocean relative to our atmosphere?

Why is the level of CO2 building up in our atmosphere ( from man's imput via combustion of fossil fuels & burning of forests if the ocean is a sink?

Below is a more quantitative representation of the carbon cycle- from this diagram we can better assess the sinks and potential sources and the rates of exchange, as we might with a Stella model format.

What proportion of carbon flow is regulated by the oceans?...by terrestrial ecosystems?

Why are we making such a deal about the % contributed by man through combustion? through deforestation?

Nitrogen cycle:
Although the carbon cycle appears complex enough, the nitrogen cycle due to its many forms and biotic interactions is even more complicated, and more rapid in exchange...

Explain the nitrogen cycling based on the following information on how much energy is either given off by the reaction (+) or required (-).

What types of critters mediate each of the reactions? how much do they gain or loss energetically with the chemical process they are involved with?

REACTION ............................ENERGY YIELD...(KILOCALORIES)

DENITRIFICATION

Denitrification - stimulated by anerobic conditions.

Denitrification Involves conversion of NO3- to N2 gas Bacteria responsible = Pseudomonas Through nitrification and denitrification 10 - 20 % of the available N is lost to the atmosphere.. it is no longer fixed.

1 C₆H₁₂0₆+ 6KNO3 --> 6 CO2 + 3H20 + 6KOH + 3N2O +545Kcal
GLUCOSE

2. 5 C₆H₁₂0₆+ 24 KNO3 -->30 CO2 + 18H20 + 24 KOH + 12 N2 +570 kcal/m glucose

3 5S + 6KNO3 + 2CaC03 --> 3 K2SO4 + 2 CaS04 + 2 CO2 + 3 N2 +132 kcal/mole of S

RESPIRATION

4. C₆H₁₂0₆+ 602 --> 6 CO2 + 6 H20 +686 kcal

AMMONIFICATION
Ammonification A. Ammonification is the conversion of organic N (R-NH2) into inorganic ammonia (NH3) R-NH2 ---> NH3 + H+ ----> NH4 + heterotrophic organ. (ammonium)

B. Fates of NH4+ = 1) fixed by clay minerals, 2) lost by soil erosion, 3) used by plants (NH4+), 4) volatilization NH4+---->NH3,

5 CH₂NH₂COOH + 1.5 O2 --> 2 CO2 + H20 + NH3 +176 kcal
GLYCINE/AA AMMONIA

NITRIFICATION
Nitrification 2 - step process 1. 2NH4+ + 3O2 ---> 2NO2- + 4H+ + 2H20 + E Nitrosomonas 2. 2NO2- + O2 --> 2NO3- + Nitrobacter Process is acid causing due to release of 4 H+ 3. Fates of Nitrate *Immobilization ---> Plant uptake of NO3- *NO3- is not held by soil particles and is *Easily leached

6 NH₃ + 1.5 02 --> HNO₂ + H20 +66 kcal
NITROUS ACID

7 KNO₂ + .5 02 --> KNO₃ +17.5 kcal
POTASSIUM NITRITE

NITROGEN FIXATION
Non-Biological Fixation -Air Pollution - nitric acid + rainfall additions from electrical discharge (lightening) 2-5 lbs/acre/year

Biological Fixation

1. Nonsymbiotic (independent organism) - Azobacter - aerobic & Clostridium - anerobic about 5-50 albs/acre/year

2. Symbiotic - mutually beneficial for host organism and bacteria. complex plant -bacteria interaction B. Symbiotic N- Fixation Bacteria = Rhizobia Plant = Legume - peas, clover, alfalfa, cowpeas, peanuts, beans, soybeans..... Alfalfa - 200 lbs/acre/year...... Soybeans - 100 lbs/acre/year...... Beans - 40 lbs/acre/year

8. N₂-->2N "ACTIVATION' OF NITROGEN - 160 kcal *

9. 2N + 3 H2 --> 2NH3 +12.8 kcal

How has man altered this nitrogen flow?

If cars can supply the 160 kcal of energy to split the N from the excess heat of the engine ( or as any combustion appliance):

N₂-->2N "ACTIVATION' OF NITROGEN - 160 kcal *
Since this reaction is occurring in an aerobic environment ,unlike the nitrogen fixation in nodules,

free 2 N can combine with O2 --> NO2 ---> in presence of UV ---> NO + O

O + O2 --> O3 and etc.

Repercussions of this are evident as in this study in Science:

Troubling Tailpipe Fertilizer (article in Washington Post 12/96)

Most people probably don't regard the family sedan as a fertilizer delivery system. But it is: Coming out of the tailpipe, along with hydrocarbons and greenhouse gases, are numerous oxides of nitrogen (NOx).They're a virtually inevitable byproduct of burning fossil fuels in air, which is 80 percent nitrogen and 20 percent oxygen. NOx mixes with water in the atmosphere and hits the dirt as nitrogen-rich rain.

Nitrogen, of course, is a major component of fertilizer. So for years, said University of Toronto ecologist David A. Wedin, some theorists hoped NOx pollution would actually have a "silver lining" because it would encourage plant growth, which would in turn suck more polluting CO2 out of the air. But Wedin and David Tilman of the University of Minnesota report in the Dec. 6 Science that such nitrogen "loading" is in fact "a major threat to grassland ecosystems."

They studied 162 controlled prairie plots in Minnesota for 12 years and found that increasing nitrogen by an amount approximately equal to what hits the soil in the combustion-dense Northeast United States had several adverse effects. Indigenous grasses gave way to nonnative species that store less carbon per unit nitrogen; less nitrogen was retained in soil; and the total number of species dropped.

In parts of northern Europe, Wedin said, NOx from the atmosphere deposits about half as much nitrogen per acre as U.S. Corn farmers use in fertilizer.That poses a substantial threat to ecosystem function and biodiversity, and not only in grasslands (about 20 percent of the world's vegetation) but everywhere NOx emissions are on the rise."The mechanisms, the way the ecosystems work, are generalizable" to many other kinds of growing areas as well, Wedin said.&.;Curt Suplee

What does this mean to all our ecosystems? this should apply only to systems impacted by man, but with increasing population and cars, more systems will be affected.

Phosphorous cycle:

As you can see from the short article below, the cycling of phosphorous can be quite complex....

TOXIC ALGAE RETURNS TO LAKE ERIE

Microcystis, a blue-green algae that is harmful to humans and deadly to plants and fish, has returned to a small area of western Lake Erie after a 10-year absence. Researchers are examining whether the reappearance of Microcystis might be associated with the recent arrival of zebra muscles, a nonnative species that was introduced to Lake Erie from Russia in 1986.

At first, the return of Microcystis baffled many researchers. It was discovered that high phosphorus levels in Lake Erie, caused by fertilizers, laundry detergent and human sewage caused the large outbreak of the algae in the 1970s. Phosphorus, is one of the most vital nutrients necessary for Microcystis growth and, as a result, millions of dollars were spent to destroy the algae by reducing phosphorus levels in Lake Erie.

By the late 1980s, the fearful blooms had ceased. So a recurring Microcystis outbreak in 1995 caught many people by surprise. David Culver, Professor of Zoology and Environmental Studies at Ohio State University, is looking into the matter in collaboration with 12 other researchers. He explains that the reoccurrence of Microcystis could be due to a change in phosphorus levels, or it could be due to the possibility that the Zebra Muscles are recycling phosphorus faster.

Culver believes the Zebra Muscles are using the phosphorus over and over again. "So a little bit (of phosphorus) goes a long way," he said. "Small changes in the reuse oh phosphorus can make it much more available." The zebra muscles may be impacting Microcystis blooms in two ways, Culver says. "By recycling nutrients that normally would have spent more time in sediment, provides more phosphorus for further algae growth." Secondly, "the zoo muscles remove Microcystis from water columns in pseudo feces, which are more readily accessed by bottom dwellers, which are in turn eaten by fish." This possibility would provide the Microcystis with better access to the food chain.

"One of the reasons we are really interested in this is because zebra muscles are continuing to expand their presence in Lake Erie. If zebra muscles are responsible for the blooms of Microcystis, we should expect the blooms to become more frequent." And that could be really bad news as Microcystis causes harm to other populations, especially humans. In people, the algae can cause vomiting, diarrhea and hepatitis-like symptoms, including intestinal cramps and liver problems.

Culver said many cities depend on water from Lake Erie. 'You can't just take water, chlorinate it and remove the toxin from Microcystis. Cities using water from Lake Erie for drinking will have to use special measures to remove the toxin." ............Source: Environmental News Network

On a more global scale......the diagram below represents the flux of P through the ecosystem...

In many ways, P cycling is simpler than that of nitrogen....

a. Has fewer steps: plants take it directly from the soil & water as PO4 and incorporate it into organic molecules. Animals excrete excess P in urine and phosphotizing bacteria released from organic matter.

b. It does not cycle in the environment in the atmosphere except as dust -- not in gaseous form. It does not undergo much oxidation-reductions as with N and C, there is only limited microbial transformations.

c. The acidity of the environment affects it's availability. At low pH it binds to clay particles tightly, and complexes with Fe and Al. At high pH it will complex with calcium. So really it most available in neutral conditions.

In an aquatic system:

Microbial role in biogeochemical cycling:
Without microbes a large proportion of these reactions could not occur. They enhance productivity by releasing these atoms from their organic forms in the process of decomposition or as in the N cycle, by nitrogen fixation.