Aquatic Nitrogen Cycle

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Aquatic Nitrogen Cycle

Dy, Manalaysay, Nasser, Son

BS BIO 4



Aquatic Nitrogen Cycle

Overall cycle is similar to terrestrial nitrogencycle, but has different players and modes of transfer of nitrogen

Nitrogen cannot be utilized by phytoplanktonso it must undergo nitrogen fixation w/c isperformed by cyanobacteria

Phytoplankton need nitrogen in biologicallyavailable forms for the initial synthesis of organic matter



What is Aquatic Nitrogen Fixation?

Aquatic nitrogen fixation is the process by w/c

nitrogen is converted bet. its various chemical

forms



Aquatic Nitrogen Fixation

fixed nitrogen a.k.a. reactive nitrogen

Cyanobacteria diazotrophs (able to fixatmospheric nitrogen)

All known nitrogen-fixing organisms areprokaryotes

N2 from the atmosphere is fixed by the enzymenitrogenase into ammonium using ATP as a

source of energy One of the most metabolically expensive

processes (requiring 16 ATP for each molecule of N2 fixed)



Ecological Function

Nitrogen is essential for many processes; crucialfor many life on earth

It is the component in all amino acids

(incorporated into proteins) It is present in the bases that make up nucleic

acids (such as DNA and RNA)

Chemical processing or natural fixation arenecessary to convert gaseous nitrogen into formsusable by living organisms (makes nitrogen acrucial component of food production)



AQUATIC NITROGEN CYCLE

BASIC PROCESSES GOVERNING THE CYCLE:1. NITROGEN FIXATION conversion of nitrogen gas (N2)

to ammonium (NH4+) by nitrogen-fixing bacteria; or by

energy from lightning; usable by some autotrophs

2. NITRIFICATION conversion of ammonium (NH4+) to

nitrate (NO3-) by nitrifying bacteria; usable by most

autotrophs

3. DENITRIFICATION conversion of nitrate (NO3-

) tonitrogen gas (N2) by denitrifying bacteria

4. ASSIMILATION uptake of usable nitrogen by

autotrophs (phytoplankton, algae, sea plants);




BASIC PROCESSES GOVERNING THE CYCLE:incorporation into organic matter via metabolism;

transfer of nitrogen in biomass to heterotrophs

(herbivory, predation, detritus feeding)

5. AMMONIFICATION/MINERALIZATION conversion of

nitrogen in organic matter (waste products/dead

organisms) to ammonium

6. SINKING/MIXING sinking of nitrogenous matter intothe substrate; re-enrichment of upper trophic layers

due to upwelling processes




FACTORS AFFECTING THE CYCLE:1. ANTHROPOGENIC nitrogen loading, pollution,

terrestrial erosion, combustion, industry

2. TERRESTRIAL RUN-OFF natural washing-off of soil,

water, and organic matter to the aquatic environment

3. DIAZOTROPHS nitrogen-fixing organisms: key to

converting unusable nitrogen into usable form

4. AUTOTROPHS incorporation of nitrogen into organicmatter (biomass)

5. WEATHER CONDITIONS lightning (high energy causes

conversion of nitrogen gas to nitrate)




FACTORS AFFECTING THE CYCLE:6. RATE OF TURN-OVER disturbances to the water

column that cause upwelling of nutrients

7. AQUATIC FLORA AND FAUNA balance of various

groups of organisms that convert nitrogen from one

form to another



Effects of Nitrogen Fixation to

the marine ecosystem



Nitrogen (N) is an essential macronutrient thenon-availability of which in suitable form orconcentration often limits biological

production both in the terrestrial and marineenvironments.

Generally, it is used to synthesize structuralcomponents, or to gain energy for growth.



Others are:

Increased plant biomass

Increased oxygen demand and hypoxia or anoxia Shifts in benthic community structure caused by anoxia and

hypoxia

Changes in phytoplankton community structure causeddirectly by nutrient enrichment

Stimulation of harmful algal blooms (HABs)

Degradation of seagrass beds

Coral reef destruction



Few microorganisms have the capability to utilize (fix) N2,

converting it to the more easily utilizable combined

nitrogen forms initially ammonia (NH3), or its protonated

species, ammonium (NH4+) that is terminally oxidized tonitrate (NO3-) by nitrifying bacteria.

Nitrification, a chemoautotrophic process, is carried out by

a consortium of bacteria and involves production of

intermediates such as nitrite (NO2-), and nitrous

oxide (N2O) as a byproduct.



The Nitrogen Cycle

Governs the primary productivity of the marine

ecosystems.

The assimilation of nitrogen by phytoplankton is

strongly linked to the photosynthetic fixation of

carbon, because both elements are needed in order

to build living organic tissue. Thus, giving us

implications for how carbon is cycled through the

system and what fraction of it is exported.



Of particular concern is the likely decrease of

the ocean interior oxygen concentration,

which is bound to increase denitrification, and

through the resulting decrease in the oceanic

nitrogen inventory will lower marine

productivity.



This would cause a release of natural CO2 from theocean, thereby accelerating the CO2 increase in theatmosphere and the resulting warming.

In addition, a decrease in the ocean interior oxygencontent will also likely increase the production andrelease of nitrous oxide, which is a much more

powerful greenhouse gas than CO2.



This is because organic nitrogen is seldom

completely converted to NO3- or N2 during

either nitrification or denitrification. Some

small fraction ends up as nitrous oxide, N2O.

Nitrous oxide acts as a greenhouse gas that is

more than 200 times more potent than CO2.



Deficiency of Nitrogen

May cause changes in the community

structure since primary and secondary

producers are dependent on CO2, NO3-, and

PO3^4¯as requirements for building living

organic tissue.



References

http://www.gcrio.org/ozone/chapter4.pdf

http://www.ciesin.org/documents/UNEParticl

e_worrest.pdf http://www.soest.hawaii.edu/oceanography/c

ourses/OCN621/Spring2011/Gruber_et_al._2

008_N_Book.pdf

http://www.eoearth.org/article/Marine_nitro

gen_cycle



Algae Capable of Nitrogen

Fixation

Cyanobacteria (Blue-Green Algae)



Cyanobacteria

Blue-green algae

Presently classified as Eubacteria; formerlythought to be closely associated w/ true algae

Photosynthetic and contain chlorophyll a

May be unicellular or multicellular

May be non-filamentous or filamentous

Have the ability to fix nitrogen ± Widespread; often more active than other nitrogen-

fixing eubacteria



Cyanobacteria

Heterocysts

± Larger than vegetative cells

± Appear empty under light microscope

±Where nitrogen fixation occurs

± Surrounded by thick cell walllimits ingress of

atmospheric gasesvirtually anoxic (ideal for

nitrogenase, an oxygen-sensitive enzyme)



Cyanobacteria

Heterocysts

Nostoc



Cyanobacteria

Heterocysts

± Develops from vegetative cells

If ammonium is present: no heterocyst formation

If available nitrogen is depleted: heterocysts develop

± Fix nitrogen and pass it to surrounding cells

through microplasmodesmata (i.e. fine holes in

their walls)



Cyanobacteria

Heterocysts

Anabaena



Cyanobacteria

Often store remaining nitrogen compounds as

cyanophycin granules in cytoplasm

± Composed of a simple polymer of aspartic acid,

each molecule of which has an attached molecule

of arginine

±When cell needs large amounts of nitrogen,

cyanophycin is depolymerized



Cyanobacteria

Examples:

± Anabaena

Grows w/ water fern Azoll a & roots of many cycads

Azoll a infected w/ Anabaena are grown in rice

paddiessome fixed nitrogen dissolves in water of

paddy, becoming available to rice plantsrice crops can

be grown in nitrogen-deficient soils



Cyanobacteria

Examples:

± Anabaena



Cyanobacteria

Examples:

± Nostoc

in parts of the body of liverworts such as Bl asi a and

Anthocer os

± in Bl asi a: occupy auricles w/c are almost spherical structures

on ventral surface of thallus

± in Anthocer os: occupy slime cavities w/in thallus that open to

ventral surface via slit-like pores



Cyanobacteria

Examples:

± Nostoc

Blasia pusilla:

globular yellow

masses of gemmae

borne on elongate

stem-like podia;dark rounded lumps

on the thallus are

colonies of Nost oc

Aquatic Nitrogen Cycle

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