2/11/2011
Nutrients, biology and elemental stoichiometry
•Subtropics and tropics: oligotrophic = low nutrient, low biomass.
biomass
•Equatorial upwelling regions: Elevated nutrients (1‐10 M NO3‐) and biomass (relative to surrounding )
waters).
•High latitude: High nutrients (10‐30 M NO3‐), elevated biomass.
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2/11/2011
Nutrients make things grow…
Where do ocean nutrients come from?
Air
Rivers
Recycling
Deep Sea
Deep Sea
1)
2)
3)
4)
Deep ocean (physics)
Recycling (biology)
River runoff (mostly physics)
Air (both physics and biology)
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Distributions of nitrate
-1
Nitrate (mol N L )
0
10
20
30
40
50
60
0
Depth (m)
1000
2000
3000
4000
Physical supply of nutrients to the upper ocean
Upwelling
Mi i
Mixing
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Biology establishes direct linkages between elemental cycles
Gruber and Galloway (2008) Nature 451: 293‐296 Organic matter production
106 CO2 + 16 HNO3 + H3PO4 + 122 H2O  (CH2O)106 (NH3)16 (H3PO4)+138O2
Consumes CO2
Produces oxygen
yg
C
Consumes nutrients
i
Aerobic remineralization of organic matter:
(CH2O)106(NH3)16H3PO4 + 138O2  106CO2 + 122H2O +16HNO3 + H3PO4
Consumes O2
Produces CO2
Recycles nutrients
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Redox states and chemical forms of nitrogen
5 stable oxidation states
Oxidized N
Transformations of N among these different compounds are controlled by microorganism growth.
Reduced N
(Sarmiento & Gruber, 2006)
Pools and pathways of nitrogen in the sea
Nitrogen as a nutrient
(nitrogen assimilation):
NO3‐
NO2‐
NH4+
DON
N2 via N2 fixation
Nitrogen as an e‐ donor (dissimilatory):
NH4+ : ammonium oxidation/annamox
NO2‐: nitrite oxidation
DON : heterotrophic catabolism
Nitrogen as an e‐ acceptor
(dissimilatory):
NO3‐ : denitirification
NO2‐ : denitrification, annamox
NO: denitrification
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• N2 : biologically inert (with a few exceptions); concentrations ~600
concentrations 600 mol L
mol L‐11
• NO3‐ : concentrations range nanomolar (surface ocean) to micromolar (deep sea)
• DON : concentrations typically 4‐6 mol L‐1 in surface ocean, decreasing with depth
• NO2‐ : concentrations typically subnanomolar
i
i ll
b
l
• N2O : concentrations typically nanomolar
• NH4+ : concentrations typically nanomolar
Nitrogen assimilation
• Nitrogen is an essential nutrient found in amino acids, protein, and nucleic acids.
id
t i
d
l i
id
• Nitrogen is assimilated by both autotrophic and heterotrophic plankton.
• Nitrogen in organic matter is reduced to the level of NH4+ (‐3 valence state).
• Most “fixed” nitrogen in the ocean exists as nitrate (most oxidized form) so energy is required to assimilate into biomass.
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Plankton production is supported by 2 types of nitrogen: 1) new production supported by external sources of N (e.g. NO3‐ and N2), 2) recycled or regenerated production, sustained by recycling of N.
‐Why does this generalization apply to the open sea but not near shore environments?
The f‐ratio Assumptions: 1) N2 fixation is low
2) Steady state system
3) Euphotic zone nitrification is low
Note NR includes regenerated forms of N uptake (historically mostly considered urea and NH4+)
Mathematical description linking new production and organic matter export. At steady state, nitrogen input is balanced by nitrogen export.
Under steady state (i.e. nitrate input balanced by export/grazing loss), if export is less than input, biomass accumulates. This biomass must eventually be exported to keep the system in steady state.
f = NO3‐ / ( NO3‐ + ∑NR)
N2
regenerated
Biological production
NH4+
export
NO3‐
NO3‐
NO2‐
NH4+
N export
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Determining the f‐ratio
• Incubate seawater in the presence of trace 15NO ‐, 15NH +, and sometimes 15N‐urea
d
ti
N
3
4
• Calculate NO3‐, NH4+, and “DON” uptake
• What makes this difficult for the oligotrophic
ocean? Duce et al. (2008)
97
Science 320: 893 ‐ 89
Not all “new” nutrients are introduced to the euphotic zone from below…
• Atmospheric deposition (both dry and wet) can form an important source of nutrients.
• Advection: lateral input of nutrients
• N2 fixation
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•N2 fixation is the primary mode of introducing “fixed” nitrogen to the biosphere.
•N2 fixation converts N2 to NH3; process is exclusively mediated by prokaryotes
•Energy expensive to break triple bond i N2
in N
N2 + 8H+ + 8e− + 16 ATP → 2NH3 + H2 + 16ADP + 16 PO43‐
Fritz Haber
Fritz Haber
Carl Bosch
Carl Bosch
• Haber‐Bosch N2 fixation: • 3CH4 + 6H2O → 3CO2 + 12H2
• 4N2 + 12H2 → 8NH3
• Requires high temperatures and pressure
• Provides nitrogen for >30% of the world’s food supply.
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Global estimate of N2 fixation based on N‐DIC drawdown in NO3‐
depleted warm waters is equivalent to 0.8 0.3 Pg C yr‐1
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Each annual cycle at HOT and BATS has significant Dissolved Inorganic Carbon (DIC) drawdown, b
but not enough h
nitrate is present in surface water to support growth. from Karl et al. in
Fasham Ocean
Fasham, Ocean Biogeochemistry
Fasham et al. (2003)
N2 fixation may also play an important role in controlling nutrient stoichiometry in the sea
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2/11/2011
TDN = 14.57(TDP) + 1.5
50
NO3- : PO43-
40
30
2
‐1
Nitrogen (mol L
NO - + NO - (mol) L-1)
TDN : TDP
3
20
Nearly identical slopes, but different intercepts
10
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Phosphorus (mol L
PO43- (mol L-1)‐1)
NO3‐= 14.62 (PO43‐) ‐ 1.08
Let’s look at dissimilatory nitrogen transformations
Oxidized N
Energy to be gained in oxidation
Reduced N
(Sarmiento & Gruber, 2006)
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Dissimilatory nitrogen transformations
NH2OH → NO → N
OH → NO → N2O
Nitrification: NH4+
Denitrification: NO3‐
Denitrification: NO
→ NO2‐
→ NO3‐
→ NO2‐ → NO → N
→ NO
→ NO → N2O → N
O → N2
Anammox: NO2 + NH4+
→ N2 + 2H2O
-1
O2 concentration (mol O2 L )
0
50
100
150
200
250
300
0
Depth (m)
1000
2000
3000
4000
N+N
O2
5000
0
10
20
-
30
-
40
50
-1
NO3 + NO2 (mol L )
(CH2O)106(NH3)16H3PO4 + 138O2 
106CO2 + 122H2O +16HNO3 + H3PO4
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Organic matter production
106 CO2 + 16 HNO3 + H3PO4 + 122 H2O  (CH2O)106 (NH3)16 (H3PO4)+138O2
Consumes CO2
Produces oxygen
yg
C
Consumes nutrients
i
Aerobic remineralization of organic matter:
(CH2O)106(NH3)16H3PO4 + 138O2  106CO2 + 122H2O +16HNO3 + H3PO4
Consumes O2
Produces CO2
Recycles nutrients
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0
De
epth (m)
1000
Pacific
Atlantic
2000
3000
4000
0
10
20
-
30
-
40
50
-1
NO3 + NO2 (mol L )
Aerobic regeneration of nitrogen
Complete decomposition of organic matter
(CH2O)106(NH3)16H3PO4 + 138O2  106CO2 + 122H2O +16HNO3 + H3PO4
Multi‐step process. First step is the breakdown of amino acids to NH4+; this process is mediated by heterotrophic microorganisms
2NH4+ + 3O2

2NO2‐ + 4H+ + 2H2O
2NO2‐ + O2

2NO3‐
These reactions yield energy (but not much…)
Nitrification:
predominately mediated by chemoautotrophic microbes (best studied are Nitrosomonas and Nitrobacter)
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Degradation of organic N to ammonium occurs during heterotrophic metabolism.
Nitrification is a 2 step process that is mediated by different groups of microbes. The first step (termed ammonium oxidation) oxidizes NH4+ to NO2‐, and the second step converts
and the second step converts NO2‐ to NO3‐. Nitrification
•Biological oxidation of NH3 to NO3‐ using yg
p
oxygen as terminal electron acceptor.
•Two step process; ammonia oxidation followed by nitrite oxidation; both reactions yield energy.
•NO2‐ serves as an important intermediate; incomplete nitrification also yields N2O.
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Oxidized N
Energy to be gained in oxidation
Reduced N
(Sarmiento & Gruber, 2006)
Recent isolation and cultivation of an abundant archaeal ammonium oxidizer
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