Isotopengeochemie

3. Stickstoffisotope

Stickstoff (N) ist unerlässlich zum Aufbau von allen Lebens. In

organischen Material tritt es vornehmlich in folgenden Formen auf:

• Nukleinsäuren

• Aminosäuren

• Proteinen

• Adenosintriphosphat (ATP)

Stickstoffgas (N2) hat mit 78% den größten Anteil am

Stickstoffreservoir der Atmosphäre und den Ozeanen. Für Leben

nutzbarer Stickstoff umfasst NO3-, NO2, N2O, NH4

+, Harnsäure,

DON und PON.

Die Verfügbarkeit dieser biologisch-verfügbaren

Stickstoffmodifikationen kontrolliert die Primärproduktion in den

Ozeanen.

Stickstoff (N)

C

14.007

Stickstoff

7

14

N

14.007

Stickstoff

7

15

Elemente des Periodensystems

14N = 99,936%; 15N = 0.364%

Elemente des Periodensystems

Rnitrogen = 15N 14N

Isotopenverhältnis

15N/14Nsample – 15N/14Nstandard

15N/14Nstandard δ15N (‰) = x 103

δ-Wert

N2

Mariner Stickstoffkreislauf

….in den 80‘ Heutiger mariner Stickstoffkreislauf

80 Tg N / yr.

10 Tg N / yr.

Mariner Stickstoffkreislauf

6

Form Formula Function Pathways Habitats

Nitrate NO3- Electron acceptor,

nitrogen source Nitrogen assimilation, dissimilatory nitrate reduction and denitrification

Coastal upwelling zones, deep ocean

Ammonium NH4+ Electron donor, energy

source, nitrogen source Nitrogen assimilation, ammonia oxidation (aerobic), and anaerobic ammonia oxidation

Important, rapidly recycled pool in open ocean, intermediate in decomposition of organic matter

Nitrite NO2- Electron donor and

acceptor, energy source, nitrogen source

Nitrification (nitrite oxidation), denitrification

Found at margins of oxic/anoxic regions, intermediate in oxidation and reduction pathways

Dinitrogen N2 Nitrogen source - High concentration in equilibrium with atmosphere, available to N2-fixing microorganisms

Nitrous oxide N2O Trace gas, electron acceptor, electron donor

End or by-product of nitrification and denitrification

Intermediate in reductive pathway, also formed in nitrification and at oxic/anoxic interfaces and anoxic or suboxic zones

Dissolved organic nitrogen

Multiple compounds, including, e.g., amino acids

Nitrogen source, nitrogen-containing organic matter, mostly poorly characterized

Remineralization (ammonification)

Complex organic matter found throghoutoceans but with varying, not well-known composition

Urea (NH2)2CO Nitrogen source Nitrogen assimilation Decomposition product, potentially important nitrogen source in water column

Stickstoffspeziationen in den Ozeanen

N2

N2 94% of all N (1x 107 Tg N)

88% of bio N

12% of bio N

PON

NO2

NH4

N2O

0.3%

Mariner Stickstoffkreislauf

N Species Surface (0-100m)

Deep (>100m)

Coastal waters

Estuarine waters

Nitrate 0.2 35 0-30 0-350

Nitrite 0.1 <0.1 0-2 0-30

Ammonium <0.5

<0.1 0-25 0-600

Dissolved organic N 5 3 3-10 5-150

Particulate Organic N 0.4 <0.1 0.1-2 1-100

N2 gas 800 1150 700-1100 700-1100

All abundances are given in μmol kg-1

Stickstoffspeziationen in den Ozeanen

Mariner Stickstoffkreislauf

N2

Mariner Stickstoffkreislauf

N2-Fixierung

N2-Fixierung Flusseintrag

Atmosphärische Deposition Brandes et al. (2007)

76 Tg N/Jahr

30 Tg N/Jahr 125-200 Tg N/Jahr

Stickstoffquellen im offenen Ozean

Biologische N2-Fixierung

Stickstofffierung tritt nur in Prokaryoten auf (grau markiert)

1. Unizellulär

2. Filamentös, nicht-heterozystös

• Chroococcales

• Pleurocapsales

• Oscillatoriales

• Nostocales

• Stigonematales

3. Filamentös, heterozystös

Cyanobakterien

Biological nitrogen fixation is the microbially mediated reduction of

N2 to NH3

N2 + 8H+ + 8e- → 2NH3 + H2

• The fixation of N2 is an energy expansive process

• Biological N2 fixation is exclusively carried out by prokaryotes

• Cyanobacteria are the predominant N2 fixers in contemporary

global oceans

Biologische N2-Fixierung

15

Nitrogenase

Nitrogenase ist ein Eisen/Molybdänproteinkomplex, dass die

Reduktion von N2 zu NH3 ermöglicht

NO3- NH4

+ N2

ε

15

10

5

20

25

Nitrogen isotopic fractionation associated with N uptake

0 (N

H4) =

15 to

25‰

(NO

3 ) = 1

to 1

0‰

(N2 ) =

0 b

is -2

‰

Nitrogen isotopic fractionation associated with N uptake

-6

-4

-2

0

2

4

δ15N

(‰

)

N2-fixing cyanobacteria NO3--utilizing species

• Diazotrophic (N2-

fixing) cyanobacteria

are characterized by

δ15N values ranging

from 0 and -2‰

• NO3--utilizing

cyanobacteria exhibit

δ15N values that are

more variable and vary

between +4 to -6%

Biologische N2-Fixierung

Trichodesmium

Trichodesmium - ein filamentöses, nicht-

heterozystöses Cyanobacterium -, das in

tropischen bis suptropischen Breiten vorkommt, in

denen die Wassertemperaturen im Mittel höher

als 23 °C sind

Tuff

Puff

„Vast quantities of little

substances….floating upon the

water in large lines a mile or so

long…either immediately upon

the surface or not many inches

under it. The seamen….began

to call it Sea Sawdust“ Joseph

Banks (1770)

Stickstofffixierung durch

Trichodesmium für 50% der

Primarproduktion im

Nordwest Pazifik

verantwortlich

Synechococcus häufig im marinen Milieu

Weit verbreitet in temperierten und tropischen

Ozeanen

Die Größe variiert zwischen 0.8 μm und 1.5 μm

Vermutlich nicht diazotroph

Crocosphaera häufig in tropischen Ozeanen

Die Größe kleiner als <1.5 μm

Diazotroph – fixiert N2 in der Nacht und CO2

am Tag

Unizelluläre Group A-B Cyanobakterien

(Group B = Crocosphaera watsonii)

Unizelluläre Cyanobakterien

• Heterocystous cyanobacteria form

symbiotical relationships with diatoms of

the genera Rhizosolenia and Hemiaulus

• Heterocystous cyanobacteria may play an

important role in the contemporary

marine nitrogen cycle

Diatom diazotroph association (DDAs)

© ESA

Aphanizomenon spp.

Nodularia spp.

Anabaena spp.

Heterozystöse Cyanobakterien

Biologische N2-Fixierung

Stickstofffixierer in den Ozeanen

Stickstofffixierer in den Ozeanen

N2 Fixierung

Stickstoffisotope in marinen Sedimenten

Nitrogen isotopic fractionation associated with N uptake

N2-Fixierung führt:

• Verringerung des δ15N Signals

• Erhöhung der biologisch-verfügbaren

Menge an Stickstoff

N2

Mariner Stickstoffkreislauf D

en

itirifikatio

n

Denitrifikation

Thiobacillus denitrificans

Denitrifikation (Nitratatmung) ist die Umwandlung

des im Nitrat gebundenen Stickstoffs zu Stickoxiden

und molekularen Stickstoff (N2) als Endprodukt zur

Energiegewinnung. Ein Prozess der unter

anoxischen/hypoxischen Bedingungen abläuft.

Denitrifikation

1. NO3+ + 2H+ + 2e- → NO2+ + H2O

2. NO2- + 2H+ + e- → NO + H2O

3. 2NO + 2H+ + 2e- → N2O + H2O

4. N2O + 2H+ + 2e- → N2 + H2O

Substrat (Elektronendonator):

• Organische Stoffe

• Molekularer Wasserstoff (H2)

• Schwefelwasserstoff (H2S)

• Ammonium (NH4+)

• Eisen(II)-Ionen (Fe2+)

• Methan

Denitrifizierung

Denitrifizierung

Nitrogen isotopic fractionation associated with N uptake

Nitrogen isotopic fractionation associated with N uptake

Nitrogen isotopic fractionation associated with N uptake

Nitrate in den Ozeanen

Stickstofffixierer in den Ozeanen

N2

Mariner Stickstoffkreislauf

Nitirifikation

39

The Redfield Ratio

The Redfield ratio is the molecular ratio of carbon, nitrogen, and phosphorous in

plankton. This empirically developed stoichiometric ratio is found to be C:N:P =

106:16:1 and is named after the American oceanographer Alfred C. Redfield.

40

The Redfield Ratio

The Redfield ratio is the molecular ratio of carbon, nitrogen, and phosphorous in

plankton. This empirically developed stoichiometric ratio is found to be C:N:P =

106:16:1 and is named after the American oceanographer Alfred C. Redfield.

41

Oceanic Nitrogen Budget

Bedeutende Cyanobakterien in den Ozeanen

A. Verteilung von

UCYN-A

Cyanobakterien

in den Ozeanen

B. Verteilung von

Crocosphaera sp.

In den Ozeanen

43

Nitrification

Nitrobacter, Nitrospina

Nitrosomonas

Nitrification is the biological oxidation of ammonium

(NH4+) with oxygen into nitrite (NO2

-) followed by the

subsequent oxidation of these nitrites into nitrates (NO3-).

Nitrification is a bacterially mediated process, in which

the first step the oxidation of ammonium to nitrite by

bacteria, usually Nitrosomonas. Nitrification continues

with the further oxidation of nitrite to nitrate by

Nitrobacter and other genera.

1. NH3 + 1.5O2 → NO2- + H2O + H+

44

Anaerobic ammonium oxidation

NH4+ + 1.32NO2

- + 0.066HCO3- + 0.13H+ →

0.26NO3- + 1.02N2 + 0.066CH2O0.5N0.15 + 2.03H2O

In the anaerobic ammonium oxidation (Anammox), nitrite and ammonium are

converted directly into dinitrogen gas.

Until the discovery of anammox in the oceans, denitrification was thought to be the

only substantial sink of combined nitrogen in the marine combined nitrogen budget.

N2 gas production in the three major oxygen deficient zones (ODZ) of the ocean

accounts for 30-50% of the total marine denitrification.

Anammox bacteria belong to the order Planctomycetes, and to date, three genera

of anammox bacteria have been identified “Candidatus Brocadia”, “Candidatus

Kuenenia” and “Candidatus Scalindua”. All marine anammox bacteria that have

been identified so far were of the genus Scalindua.

45

Anaerobic ammonium oxidation

46

Anaerobic ammonium oxidation

47

Anaerobic ammonium oxidation