Nitrogen in the Environment Flashcards
1
Q
Structure
A
- Nitrogen cycle
2.
3.
2
Q
nitrogen cycle - the basics
A
- constant
3
Q
Nitrogen cycle
A
i) fixation
ii) nitrification
iii) assimilation
iv) ammonification
v) denitrification
vi) anammox
4
Q
fixation
A
- N2 + 8H -> NH3 + H2
5
Q
NH3
A
- immobile gas?
6
Q
N2
A
atmospheric
7
Q
NH4+
A
- anhydrous
- sticks
8
Q
nitrification
A
- NH4+ -> NO2- (E0’: +0.34V)
- NO2- -(nitrite oxidoreductase)-> NO3- (E0’: +0.43V)
- oxidation (requires e’ flow x2)
- very small energetic output
- high turnover
- major process in well-drained soils
- inhibited by nitrapyrin
- Nitrosomonas
- Nitrosopumilis (Archaea; outnumber bacteria)
9
Q
assimilation
A
- NO3- -(NAPH, cytosol)-> NO2-
NO3- -(ferrodoxin, chloroplast)-> organic N
10
Q
ammonification
A
- organic N -> NH4+
11
Q
denitrification - the basics
A
- NO3- -> N2/N2O
- anoxic
- bacteria use nitrate reductase in anaerobic respiration
- nitrate is TEA
- E. coli, Bacillus, Paracoccus denitrificans, Pseudomonas stutzen
- DNRA
12
Q
N2O
A
- GHG
- 300x ^ potency than CO2
- persists for 100y
- O3 -> HNO2 (depletion)
13
Q
anammox
A
- NH4+ + NO2- -> N2
- NO2-: e- acceptor
- Brocadia
- anoxic
14
Q
Brocadia
A
uncultured
15
Q
Nitrogen losses to the environment
A
- 15% by ammonification (as NH3)
- most by denitrification, anammox
16
Q
DNRA
A
- dissimilatory NO3- reduction
- nutrient rich, anoxic envrt
- NO3- + 8H+ + 8e- -> NH4+ + 2H2O
17
Q
commamox
A
- complete ammonia oxidation
- NH3 -> NO3-
- dismutation
- Nitrospira
18
Q
dismutation
A
oxidation and reduction of the same species within the same reaction by one organism
19
Q
free-living aerobic N2 fixing bacteria
A
Azotobacter, Klebsiella
20
Q
free-living, anaerobic N2 fixing micro-organisms
A
- Clostridium
- Rhodobacter
- Heliobacteria
- Methanobacterium (archaea)
21
Q
symbiotic N2 fixing bacteria
A
- Rhizobium
- Bradyrhizobium
- Frankia
22
Q
E0’
A
- the standard redox potential
- energy suppled
23
Q
Nitrosomas
A
- NH3 -(AMO)-> hydroxylamine
- hydroxylamine -(HAO)-> O2
- releases 4 e-s; used for proton motive force
- NADH reverse transport
24
Q
AMO
A
- ammonia mono-oxygenase
- catalyses ammonia oxidation
25
HAO
- hydroxylamine oxidoreductase
26
nitrate reductase
requires molybdenum
27
Nos
- nitrous acid reductase
- requires Cu
28
Cu-deficient soils
almost always release more N2O
29
Stepwise denitrification reactions
i) NO3- -(nitrate reductase)-> NO2-
ii) NO2- -(nitrite reductase)-> NO
iii) NO -(nitric oxide reductase)-> N2O
iv) N2O -(nitrous oxide reductase)-> N2
30
NO
nitric oxide
31
N2O
nitrous oxide
32
nifHDK
- NifH homodimer
33
NifH homodimer
- 3Myo
- only one side is active
- KCAT = 5.5 (v. slow)
- forms dinitrogenase reductase
- needs Fe
- the "Fe protein"
33
NifDK
- heterotetramer dinitrogenase
- requires Fe, Mo
- the "MoFe protein"
- 4Fe, 4SO4 clusters; electron transfer
34
FeMoCo Mo-Fe7-S9-homocitrate
- nitrogenase cofactor
- N2 -> NH3
35
Engineering nitrogenase
KCAT = 11
36
Anabaena vinelandii
- O2 = 2.5%
37
nitrogenase
- v. sensitive to O2
- breaks down in air
- 1/2life = a few minutes
- reduced many triple bonded structures
- C2H2 -> C2H4
38
Nitrogenase mechansim
i) pyruvate reduces flavodoxin via pyruvate ferrodoxin reductase
ii) Fe protein receives e's from flavodoxin
iii) Fe protein oxidises ATP; reduced redox potential
iv) donates e's to MoFe protein
v) 2e' reduction intermediates protect nitrogenase from O2
vi) H2 byproduct can be used as energy source
39
What is needed to fix each N2?
- 8e-s
- 16 ATPs
- v. expensive
40
How to protect nitrogenase from O2?
- burn O2 (costly)
- slime
41
heterocysts
- specialised cells w/ thick walls to keep O2 out
- refractile, dense
- provide N2 to neighbouring vegetative cells in a filamentous chain
- "micro-aerobic N2 fixation"
42
C2H2
acetylene
43
C2H4
ethylene
44
global N2 fixation
- 413 Tg N/year
45
fertiliser
- doubled use
- doubles rate of N2 fixation in crop
46
BNF
- biological nitrogen fixation
- land: ~58 +/-50%
- sea: ~140 +/- 50%
- lightening: ~5 +/-50%
47
ANF
- anthropogenic nitrogen fixation
- Haber-Bosch: 120 +/-10%
- agriculture: 60 +/-30%
- combustion: 30+/-10%
- total = 210 (>50%)
48
combustion
- fossil fuels
- vehicles
- industry
49
fertiliser + agriculture
3z > BNF on land
50
Nr
- reactive nitrogen
- fluxes
51
N2 processes
1. biological uptake
2. transport
3. denitrification
4. atmospheric deposition
52
nitrogen oxides
- NO
- NO2
- N2O
- HNO3
- NH4NO3
- aerosols
- participate in atmospheric reactions
53
NO, NO2
interconvert in ozone reactions
54
lifespan of NOy, NHx in the atmosphere
<1mo
55
lifespan of NOy, NHx on land
<10-50years
56
lifespan of NOy, NHx in the sea
- 10-100years
57
dry and wet deposition delivers
70Tg oxidised and reduced nitrogen back to earth's surface
58
oxidised nitrogen
- NO3-
- HNO3
59
reduced nitrogen
NH3
60
atmospheric transport
30Tg N/year
61
nitrogen input into soils + plants
- organic matter
- microbial decomposition
- fertilisers
- 240Tg
62
biomass burning and fossil fuel combustion
- release nitrogen gases
- NO: 40Tg
- N2O: 13Tg
63
nitrogen leaching
80 Tg
64
oceanic denitrification
- 100-280 Tg
- returned as N2/N2O (g)
65
ocean sedimentation
20 Tg
66
The Nitrogen Cycle within the EU-27
- natural nitrogen cycling
- intentional anthropogenic flux
- unintentional anthropogenic flux
67
natural nitrogen cycling
- BNF in crops and semi-natural soils
68
International anthropogenic fluxes
- livestock farming (waste)
- fertiliser application
69
unintentional anthropogenic fluxes
- emissions
- runoff (enters wastewater system; the sea -> ecological impacts/landfill)
- leaching
70
sources
- fossil fuel combustion
- biomass burning
- soils + agriculture
- oceans
71
fossil fuel combustion
30 NOx
72
biomass burning
- agricultural
- wildfires
- 5 NOx
- 4 anthropogenic
73
soil + agriculture
- NH3: 60 (2/3 anthropogenic)
- NO: 5 (1 anthropogenic)
- N2O: 13 (7 anthropogenic)
74
oceans
- NH3: 9
- N2O: 5.5 (3 anthropogenic)
75
atmospheric processes
- photochemical reactions
- aerosol formation
76
photochemical reactions
- NOx -> O3
77
aerosol formation
- NO2 + OH. -> HNO3
- NH3 + HNO3 -> NH4NO3
78
Marine Nr input fluxes
- riverine flux
- groundwater flux
- atmospheric deposition
- BNF
79
riverine flux
- 40-70
- agriculture, livestock etc.
80
groundwater flux
- 4
81
atmospheric deposition
- 30
- air pollution (NOx, NH3); wet and dry deposition
82
BNF
- 140
- cyanobacteria
83
Marine Nr output fluxes
- burial
- gas emissions
84
burial
- 20
- sediments
85
gas emissions
- N2O: 5.5
- NH3: 9
86
NH3 can undergo
volatilisation
87
Open Ocean Cycling
- 230
- supports marine life, biochemical processes
- ecosystem level
88
Planetary Boundaries
- processes that are critical for maintaining the stability and resilience of the Earth system
- quantifying anthropogenic perturbation
- human activities have brought Earth outside of the Holocene's window of environmental variability
- a state without analog in human history
89
Which planetary boundaries have we transgressed?
1. biogeochemical flows
2. climate change
3. biosphere integrity
4. novel entities
5. land system change
6. freshwater change
90
ocean hypoxia
around areas of agriculture
91
where is phosphorus highly uncertain?
- Northern India
- SEA
- Central America
- Central Europe
92
where is nitrogen highly uncertain?
- Northern India
- SEA
- Central America
- Northern Europe
93
where is land system change highly uncertain?
- central Africa
- South Asia
94
where is freshwater use highly uncertain?
- Central Asia
- West Europe
- West America
95
nitrogen input
50% is not taken up
96
Where is nitrogen input the highest?
- USA
- Europe
- SEA
- SA
97
nitrogen scarcity
- much of Africa
- Central Asia
98
legumes
- do not require fertiliser
- enrich the soil
