3. Stickstoffisotope · 2019. 5. 21. · 44 Anaerobic ammonium oxidation NH 4 + + 1.32NO 2--+...
Transcript of 3. Stickstoffisotope · 2019. 5. 21. · 44 Anaerobic ammonium oxidation NH 4 + + 1.32NO 2--+...
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