Fundamentals of Nitrogen Cycle

8/4/2019 Fundamentals of Nitrogen Cycle

1/19

4/21/12

Click to edit Master subtitle style

FUNDAMENTALS OFNITROGEN CYCLE


2/19

4/21/12

The nitrogen cycle is the set ofbiogeochemical processes by whichnitrogen undergoeschemical reactions, changes form,and moves

Nitrogen is required for all organisms

to live and grow because it is theessential component ofDNA, RNA,and protein. However, most

organisms cannot use atmosphericnitro en, the lar est reservoir.
http://www.visionlearning.com/library/pop_glossary_term.php?oid=2179&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=1547&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2171&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=1604&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=1605&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=1594&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2171&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2171&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=1594&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=1605&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=1604&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2171&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=1547&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2179&l=%27,%27Glossary


3/19

4/21/12

The five processes in the nitrogencycle -- fixation, uptake,mineralization, nitrification, anddenitrification -- are all driven bymicroorganisms.
http://www.visionlearning.com/library/pop_glossary_term.php?oid=2180&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2181&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2182&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2182&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2181&l=%27,%27Glossaryhttp://www.visionlearning.com/library/pop_glossary_term.php?oid=2180&l=%27,%27Glossary


4/19

4/21/12

NITROGEN

CYCLE

Nitrogen (N) is

an essentialcomponent of
http://www.visionlearning.com/library/pop_glossary_term.php?oid=1605&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1604&l=


5/19

4/21/12

The inert nature of N2 means thatbiologically available nitrogen is often

in short supply in natural ecosystems,limiting plant growth and biomassaccumulation.

Nitrogen is an incredibly versatileelement, existing in both inorganicand organic forms as well as manydifferent oxidation states. The

movement of nitrogen between theatmosphere, biosphere, andgeosphere in different forms is

described by the nitrogen cycle(Fi ure 1), one of the ma or
http://www.visionlearning.com/library/pop_glossary_term.php?oid=4221&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2174&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2175&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1510&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2176&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2177&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2178&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2178&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2177&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2176&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1510&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2175&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2174&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=4221&l=


6/19

4/21/12

Nitrogen Cycle:

Figure 1:Thenitrogen

cycle.Yellowarrowsindicate

humansourcesofnitrogento the


7/194/21/12

Five mainprocesses cycle

nitrogen throughthe biosphere,atmosphere, andgeosphere:

nitrogen fixation,nitrogen uptake(organismalgrowth), nitrogen

mineralization

As microbiallymediated

processes, thesenitrogentransformationstend to occur

faster thangeologicalprocesses likeplate motion, a

very slow, purely
http://www.visionlearning.com/library/pop_glossary_term.php?oid=2177&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2183&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2180&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2180&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2183&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2177&l=


8/194/21/12

Figure 2:

Part of aclover rootsystembearingnaturallyoccurringnodules ofRhizobium,bacteria thatcan fixatmospheric

nitrogen.Each noduleis about 2-3mm long.


9/194/21/12

Nitrogen fixationN2 NH4+ Nitrogen fixation is the

process wherein N2 is converted toammonium, essential because it is the

only way that organisms can attainnitrogen directly from the atmosphere.Certain bacteria, for example thoseamong the genusRhizobium, are the

only organisms that fix nitrogen throughmetabolic processes. Nitrogen fixingbacteria often form symbiotic

relationships with host plants. Thiss mbiosis is well-known to occur in the
http://www.visionlearning.com/library/pop_glossary_term.php?oid=2183&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2171&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=886&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2184&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2184&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=886&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2171&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2183&l=


10/19

4/21/12

In addition to nitrogen fixing bacteria, high-energynatural events such as lightning, forest fires, and

even hot lava flows can cause the fixation ofsmaller, but significant amounts of nitrogen(Figure 3). The high energy of these naturalphenomena can break the triple bonds of N2molecules, thereby making individual N atoms

available for chemical transformation.

Within the last century, humans have become asimportant a source of fixed nitrogen as all naturalsources combined. Burning fossil fuels, using

synthetic nitrogen fertilizers, and cultivation oflegumes all fix nitrogen. Through these activities,humans have more than doubled the amount offixed nitrogen that is pumped into the biosphereevery year (Figure 3), the consequences of whichare discussed below.
http://www.visionlearning.com/library/pop_glossary_term.php?oid=1497&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1518&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1509&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2177&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2177&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1509&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1518&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1497&l=


11/19

4/21/12

Figure 3: Recent

increases inanthropogenic Nfixation in relationto natural Nfixation. Modified

from Vitousek, P. M.and P. A. Matson(1993). Agriculture,the global nitrogencycle, and trace gasflux. TheBiogeochemistry ofGlobal Change:Radiative TraceGases. R. S.Oremland. New

York, Chapman andHall: 193-208.


12/19

4/21/12

Nitrogen uptake

NH4+ Organic N The ammoniaproduced by nitrogen fixing bacteriais usually quickly incorporated into

protein and other organic nitrogencompounds, either by a host plant,the bacteria itself, or another soil

organism. When organisms nearerthe top of the food chain (like us!)eat, we are using nitrogen that hasbeen fixed initially by nitrogen fixing

bacteria.


13/19

4/21/12

Nitrogen mineralization

Organic N NH4+ After nitrogen isincorporated into organic matter, it isoften converted back into inorganic

nitrogen by a process called nitrogenmineralization, otherwise known asdecay. When organisms die,

decomposers (such as bacteria andfungi) consume the organic matter andlead to the process of decomposition.During this process, a significant

amount of the nitrogen contained
http://www.visionlearning.com/library/pop_glossary_term.php?oid=2180&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2171&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2171&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2180&l=


14/19

4/21/12

Nitrification

NH4+ NO3- Some of the ammoniumproduced by decomposition isconverted to nitrate via a process

called nitrification. The bacteria thatcarry out this reaction gain energy fromit. Nitrification requires the presence ofoxygen, so nitrification can happen

only in oxygen-rich environments likecirculating or flowing waters and thevery surface layers of soils andsediments. The process of nitrificationhas some im ortant conse uences.


15/19

4/21/12

Denitrification

NO3- N2+ N2O Through denitrification,oxidized forms of nitrogen such asnitrate and nitrite (NO2-) are converted

to dinitrogen (N2) and, to a lesserextent, nitrous oxide gas.Denitrification is an anaerobic process

that is carried out by denitrifyingbacteria, which convert nitrate todinitrogen in the following sequence:NO3- NO2- NO N2O N2.

Nitric oxide and nitrous oxide are both


16/19

4/21/12

Human alteration of the N cycle andits environmental consequences:

Early in the 20th century, a Germanscientist named Fritz Haber figured outhow to short circuit the nitrogen cycle

by fixing nitrogen chemically at hightemperatures and pressures, creatingfertilizers that could be added directly

to soil. This technology has spreadrapidly over the past century, and,along with the advent of new cropvarieties, the use of synthetic nitrogen

fertilizers has led to an enormous boom


17/19

4/21/12

Not all of the nitrogen fertilizer appliedto agricultural fields stays to nourish

crops. Some is washed off ofagricultural fields by rain or irrigationwater, where it leaches into surface orground water and can accumulate. Ingroundwater that is used as a drinkingwater source, excess nitrogen can leadto cancer in humans and respiratory

distress in infants. The U.S.Environmental Protection Agency hasestablished a standard for nitrogen indrinking water of 10 mg per liter

nitrate-N. Unfortunately, many systems
http://www.visionlearning.com/library/pop_glossary_term.php?oid=3904&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2119&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=3900&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=3904&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=3904&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=3900&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2119&l=


18/19

4/21/12

Reactive nitrogen (like NO3- and NH4+)present in surface waters and soils, can

also enter the atmosphere as thesmog-component nitric oxide (NO) andthe greenhouse gas nitrous oxide(N2O). Eventually, this atmosphericnitrogen can be blown into nitrogen-sensitive terrestrial environments,causing long-term changes. For

example, nitrogen oxides comprise asignificant portion of the acidity inacid rain which has been blamed forforest death and decline in parts of

Europe and the Northeast United
http://www.visionlearning.com/library/pop_glossary_term.php?oid=2188&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2190&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2190&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=2188&l=


19/19

4/21/12

Currently, much research is devoted to

understanding the effects of nitrogenenrichment in the air, groundwater, andsurface water. Scientists are also

exploring alternative agriculturalpractices that will sustain highproductivity while decreasing thenegative impacts caused by fertilizer

use. These studies not only help usquantify how humans have altered thenatural world, but increase ourunderstanding of the processesinvolved in the nitro en c cle as a

Fundamentals of Nitrogen Cycle

Documents

Transcript of Fundamentals of Nitrogen Cycle