2/19/2016
Are Oxygen Limitations an Under Recognized Regulator of
Carbon Turnover in Upland Soils?
Controls on C mineralization (oxidation) rates
CO2
Marco Keiluweit
plant carbon (I)
Stanford University
Tom Wanzek
and Markus Kleber
kmin
MO
Oregon State University
microbial
products
Peter Nico
Lawrence Berkeley National Lab
preserved plant
material
Scott Fendorf
mineralization rate
CO2
Molecular structure
Mineral-organic
associations
Physical separation
recycling
stored
carbon
Stanford University
DOC + DIC
Oxygen limitations?
SSSA 2015, Minneapolis, MI, Nov 17, 2015
adapted from Gleixner et al. (2013) Ecological Research
Modeling controls on C oxidation rates
Guiding questions
Uncertainties:
 anaerobic pore space
 impact on overall C
oxidation rates
 metabolic constraints
under anaerobic
conditions
1. What is the extent of the anaerobic pore
volume in upland soils?
2. How do anaerobic microsites impact
microbial metabolism and C oxidation rates?
3. Are anaerobic conditions a major control on
C turnover?
e.g., CLM-BeTR: Tang et al. 2013; Riley et al. 2014
Guiding questions
Quantifying the extent of the anaerobic pore volume
2 cm
‘Aggregate’ model
Arah and Vinten (1995) EJSS
1. What is the extent of the anaerobic pore
volume in upland soils?
¶Coxygen
¶t
= Supply - Demand
2. How do anaerobic microsites impact
microbial metabolism and C oxidation rates?
0%
3. Are anaerobic conditions a major control on
C turnover?
Sexstone et al.
(1985) SSSAJ
O2 concentration = 21%
1
2/19/2016
Quantifying the extent of the anaerobic pore volume
Quantifying the extent of the anaerobic pore volume
Field setting:
Macro-pore structure:
10 cm
10 cm
20 cm
50 cm
100 cm
Thomas Wanzek (OSU)
Defining Functional Soil Metabolic
Heterogeneity
Thomas Wanzek (OSU)
Defining Functional Soil Metabolic
Heterogeneity
Wed 2:30 – 4:30
Wed 2:30 – 4:30
Poster #326
= Pt redox probe
1 cm
5 cm
Is ‘aggregate’ model applicable?
Poster #326
Quantifying the extent of the anaerobic pore volume
Quantifying the extent of anaerobic microsites
Imaging anaerobic microsites:
Bulk oxygen concentrations
O2 saturation
Mn2+ mg g-1
O2 sensitive film
120
250 µm
incubations
planar optode imaging
oxygen saturation (%)
100
< 5% O2 saturation
80
60
40
WA-20
WA-100
AM-20
AM-100
20
0
0
10
20
30
time (days)
Quantifying the extent of anaerobic microsites
Fe reduction
Fe2+ mg g-1
soil cores
Mn reduction
Quantifying the extent of anaerobic microsites
clay-rich domains?
O2 saturation = 89%
3D - Tomography
fanoxic = 4%
120
120
100
250 µm
80
O2 saturation = 57%
60
fanoxic = 12%
40
WA-20
WA-100
AM-20
AM-100
20
0
0
10
20
time (days)
30
oxygen saturation (%)
oxygen saturation (%)
100
C hotspots?
80
60
40
WA-20
WA-100
AM-20
AM-100
20
O2 saturation = 44%
fanoxic = 12%
0
0
10
20
time (days)
30
pore space
solids
O2 saturation = 44%
fanoxic = 12%
2
2/19/2016
Thermodynamic constraints on anaerobic carbon
oxidation: FT
Guiding questions
RateC-oxidation = Rmax  X  Fk  FT
1. What is the extent of anaerobic microsites in upland
soils?
A
Thermodynamic Fdriving
force, Ft
t
1.0
2. How do anaerobic microsites impact microbial
metabolism and C oxidation rates?
3. Are anaerobic microsites a major control on C
turnover?
0.5
O2
-
NO3
Mn(IV)
Fe(III)
SO24
1.0
0.0
-3
-2
-1
0
Jin and Bethke (2005) GCA
LaRowe and Van Cappellen (2012) GCA
1
2
3
NOSC
NOSC = Nominal oxidation
B state of carbon = -((4C + H -3N – 2O + 5P – 2S)/C) + 4
Ft
+ preservation under anaerobic conditions
Lipids
0.5
fatty acids
alkanes
Unsaturated
sterols hydrocarbons
O2
lignin
Soil OM
components
NO3
carbohydrate
protein
Mn(IV)
Fe(III)
SO24
Simple amino acids
amines
Aromatic/S-containing
Nucleic acids
Condensed aromatics
tannins
0.0
-3
-2
-3
succinate
(C4H6O4 )
RateC-oxidation = Rmax  X  Fk  FT
A
A
0.5
O2
NO
3
Mn(IV)
Fe(III)
SO24
1.0
0.0
-3
-2
-1
0
1
2
3
succinate
(C4H6O4 )
-
NO3
Mn(IV)
Fe(III)
SO24
1.0
0.0
-3
-2
-1
0
1
2
3
NOSC = Nominal oxidation
B state of carbon = -((4C + H -3N – 2O + 5P – 2S)/C) + 4
Ft
Ft
+ preservation under anaerobic conditions
Lipids
Unsaturated
sterols hydrocarbons
Soil OM
components
O2
O2
carbohydrate
protein
Condensed aromatics
Mn(IV)
Fe(III)2
1
SO24
tannins
0.0
-2
-1
-1
-2
0
+1
0
NOSC
1.0
0.0
NO3
Nucleic acids
NOSC
Thermodynamic constraints in anaerobic microsites
-1
0
1
2
3
O2
lignin
Mn(IV)
Fe(III)
SO24
+2
Unsaturated
sterols hydrocarbons
Soil OM
components
NO3
-
Simple amino acids
amines
Aromatic/S-containing
-3
fatty acids
alkanes
lignin
-3
Lipids
0.5
fatty acids
alkanes
NO3
carbohydrate
protein
Mn(IV)
Fe(III)
SO24
Simple amino acids
amines
Aromatic/S-containing
Nucleic acids
Condensed aromatics
tannins
0.0
3
-3
3
-2
-3
-2
-1
-1
0
0
NOSC
+1
1
+2
2
3
3
NOSC
Impact on microbial metabolism and C oxidation
O2, pH, HSprofiling
NOSC
B
2
NOSC
+ preservation under anaerobic conditions
0.5
-2
3
+2
O2
3
NOSC = Nominal oxidation
B state of carbon = -((4C + H -3N – 2O + 5P – 2S)/C) + 4
-3
1
0.5
NOSC
0.5
+1
0
1.0
Thermodynamic Fdriving
force, Ft
t
Thermodynamic Fdriving
force, Ft
t
1.0
0
NOSC
butyrate
(C4H8O2)
RateC-oxidation = Rmax  X  Fk  FT
1.0
Thermodynamic Fdriving
force, Ft
t
A
-1
-1
-2
NOSC
Thermodynamic constraints on anaerobic
carbon
oxidation: electron donor
Thermodynamic constraints on anaerobic carbon
oxidation: electron acceptor
Ft
lower
oxidation rates
in anaerobic
anaerobicconditions
microsites?
+ preservation
under
oxygenated
water
Lipids
0.5
fatty acids
alkanes
Unsaturated
sterols hydrocarbons
O2
lignin
Soil OM
components
protein
Nucleic acids
Condensed aromatics
tannins
0.0
-3
-3
-2
-2
-1
-1
0
0
NOSC
+1
1
solid + solution
phase analysis
Mn(IV)
Fe(III)
SO24
Simple amino acids
Aromatic/S-containing
anaerobic
NO3
carbohydrate
amines
CO2, CH4, DOC
aerobic
+2
2
3
3
NOSC
Rule set adapted from:
Canfield et al. (1993) Geochimica et Cosmochimica Acta 57, 3867–3883
Canfield et al. (1993) Marine Geology 113, 27-40
3
-
O2 saturation (%)
0
0
50
00
aerobic respiration
0
Fine
AerobicR
- 41%
AnaerobicR
5
10
3
10
100
00
505
00
Mn
reduction
denitrification
denitrification
aerobic
respiration
2/19/2016
2+
2+
Fe
(mM)
Mn
(mM)
(aq)
(aq)
100
10
50
50
2+
Fe(aq) (mM)
100
100
0
4
5
coarse
fine
6
100 0.00
Impact on microbial metabolism and0 C 50oxidation
2+
-1
Mn(HCl) (mg g soil)
-1
C oxidation rate (mmol C d )
metabolic rates:
density fractionation:
change in TOC (%)
AerobicR
100
Fe reduction
3
6
15
50
Mnreduction
reduction
Fe
2
coarse
fine
5
Impact on microbial metabolism and C oxidation
0
2
4
- 32%
550
1
depth (cm)
depth (cm)
1
Coarse
2+
Mn
(mM)
NO
(mM)
(aq)
3(aq)
(mM)(%)
O2NO
saturation
3(aq)
100
-20
0
0.5
1.0
50
100
2+ 2+
-1-1
Fe
(mg
Mn
(mggg soil)
soil)
(HCl)
(HCl)
0.0
0.5
1.0
2+
-1
Fe(HCl) (mg g soil)
TOC (%) change
changeininPOC
DOC(%)
(%)change
change
in POC(%)
(%) change in MaOC (%)
change in DOC
in MaOC
-20 0
20
-40 0 0 50 40
-50
0
50
-40
40
-50
-50-50 0 0 5050
20
- 91 to 94%
anaerobic
2
3
-1
0
0
1
1
aerobic
-3
C oxidation rate (mmol C d cm )
2
3
anaerobic
Denitr.
MnR
FeR
SulfR
Methgen.
Total
2
3
4
4
= 79 to 82%
5
5
6
6
0.0
Over 30 days:
1
depth (cm)
0
aerobic
depth (cm)
AnaerobicR
0.5
1.0 4
8
too
to
12
to to
to t o
to
Over 30 days:
-1
C oxidation rate (mmol C d )
1) Oxidation rates in anaerobic zone decrease by 90%
1) Oxidation rates in anaerobic zone decrease by 90%
2) Less oxidation of bioavailable C in anaerobic zone
Impact on microbial metabolism and C oxidation
Guiding questions
change in oxidation state (%)
C NEXAFS characterization:
(COOH/C-ar)
-50
0
50
1. What is the extend of anaerobic microsites?
aerobic (0-0.5 cm)
aerobic
+250%
+15%
anaerobic
+15%
2. How do they impact microbial metabolism and C
oxidation rates?
DOC
POC
MaOC
3. Are anaerobic microsites a major control on
C turnover?
anaerobic (4-6 cm)
Over 30 days:
to
1) Oxidation rates in anaerobic zone decrease by 90%
2) Less oxidation of bioavailable C in anaerobic zone
3) Accumulation of reduced C, especially in bioavailable pools
Impact on C turnover in upland soils
Impact on C turnover in upland soils
Poorly-drained
Well-drained
Poorly-drained
Redox potential
E (mV)
(mV)
Redox potential (mV)
Eh (mV)
h
500 100
700 300
100 500
300 700
500 100
700 300
100 500
300 700
500 100
700 300
300
20
20
Depth (cm)
Depth (cm)
100
45
70
10
10
20
20
45
20
20
45
45
45
45
70
70
70
70
70
100
100
100
100
100
100
130
130
500
700
Carbon stock (g Carbon
kg-1) stock (g kg-1)
0
5
015
10
50
10
1
215 3 0 4 1 0 2 1 32
43
4 05 1
2
3
4
5
0
Depth (cm)
0
Depth (cm)
Well-drained
40
80
120
160
0.0
40
80
120
160
0.4 0.0
0.6 0.2
0.0 0.4
0.2 0.6
0.4 0.0
0.6 0.2
0.0 0.4
0.2 0.6
0.4 0.0
0.6 0.2
0.2
Feo/Fed
0
3
6
9 012 3 0 6 3 9 612 9 012 3 0 6 3 9 612 9 012 3
C/N ratio
0.4
0.6
Feo/Fed
C/N ratio
6
9
12
4
2/19/2016
Impact on C turnover in upland soils
Impact on C turnover in upland soils
density fractionation
0.4
FT-ICR-MS of subsoil extracts
poorly-drained
well-drained
Particulate OC (POC)
POC/MaOC
Well-drained
vs.
mineral-associated OC (MaOC)
Nominal oxidation state of carbon
(NOSC)
0.2
methanol
water
Poorly-drained
0.0
20
Poorly-drained soil show:
100
-1.0
Poorly-drained soil show:
depth (cm)
1) relative accumulation of particulate OC
-0.5
0.0
0.5
1.0
NOSC
1) relative accumulation of particulate OC
2) shift towards lower NOSC
Are oxygen limitations an under recognized regulator
of C turnover in upland soils?
Impact on C turnover in upland soils
Well-drained
Poorly-drained
Lipids
Anaerobic microsites …
Lipids
1) exist even at moderate moisture
contents (50% WFPS).
Lipids = 38%
A
1) reduce C oxidation rates by 90%,
with Fe reduction as the most
important respiratory pathway.
Lipids = 49%
A
1.0
1) greater relative abundance of particulate OC
1) constrain metabolism of
bioavailable, reduced C
compounds.
2) shift towards lower NOSC
3) greater relative abundance of lipids
0.5
O2
-
NO3
Mn(IV)
Fe(III)
SO24
1.0
B
0.5
O2
-
NO3
0.0
Thermodynamic
constraints
in anaerobic
microsites
-3
-2
-1
0
1
2
3
NOSC
B
Oxidation coupled to Fe
+ preservation under anaerobic conditions
reduction NOT favorable
Ft
Ft
Lipids
Unsaturated
sterols hydrocarbons
O2
protein
Mn(IV)
Fe(III)
SO24
Simple amino acids
amines
Aromatic/S-containing
Nucleic acids
Condensed aromatics
tannins
0.0
-3
-2
-2
-1
-1
0
0
NOSC
+1
1
+2
2
Unsaturated
sterols hydrocarbons
O2
lignin
NO3
carbohydrate
Oxidation coupled to Fe
reduction favorable
fatty acids
alkanes
lignin
Soil OM
components
-3
Lipids
0.5
fatty acids
alkanes
NOSC
anaerobic conditions:
Oxidation is uninhibited
+ preservation under anaerobic conditions
0.5
Mn(IV)
Fe(III)
SO24
1.0
0.0
Thermodynamic
constraints
in anaerobic
microsites
-3
-2
-1
0
1
2
3
aerobic conditions:
1.0
Thermodynamic Fdriving
force, Ft
t
Thermodynamic Fdriving
force, Ft
t
Poorly-drained soil show:
3
3
NOSC
NOSC = Nominal oxidation state of carbon = -((4C + H -3N – 2O + 5P – 2S)/C) + 4
Soil OM
components
NO3
carbohydrate
protein
Mn(IV)
Fe(III)
SO24
Simple amino acids
amines
Aromatic/S-containing
Nucleic acids
Condensed aromatics
tannins
0.0
-3
-3
-2
-2
-1
-1
0
0
NOSC
+1
1
+2
2
3
3
NOSC
NOSC = Nominal oxidation state of carbon = -((4C + H -3N – 2O + 5P – 2S)/C) + 4
5
2/19/2016
Thank you for your attention!
Acknowledgements
Stanford:
Kaitlyn Gee
Amanda Denney
Kristin Boye
Guangchao Li
Doug Turner
EMSL:
Malak Tfaily
Canadian Light Source:
Tom Regier
Jay Dynes
Earth Sciences Division
Beamlines 1.4.3, 5.4, 5.3.2, 8.3.2, 10.3.2
and 11.0.2 at the Advanced Light Source
Lawrence
Berkeley
Laboratory Directed
Research
and National Laboratory:
DulaLawrence
ParkinsonScholar
(ALS, 8.3.2)
Development Program,
Marco Voltollini (ESD)
Program
Funding:
Office of Biological and Environmental Science:
This research
by the Terrestrial
Ecosystem Science (TES) program within the
Climatewas
andfunded
Environmental
Science Division
Department of Energy (DOE) Office of Science's Office of Biological and Environmental Research
(BER), under Contract No. DE-FG02-13ER65542.
The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy
Sciences, under Contract No. DE-AC02-05CH11231.
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