Objectives - Understand and model the new paradigm of soil carbon (C) stabilization at the C-microbe-mineral interface with varying: -Carbon input chemistry -Microbial community composition, and -Soil mineralogy - Integrate findings across spatial (molecular to landscape) and temporal scales using: Gradients of soil age (~40 to 250 ka), and climate (~300 to 1200 mm yr-1) - Incorporate improved mechanistic understanding of C stabilization/destabilization into new reactive transport models

1. Microbe-mineral interactions and the fate of
soil carbon
Courtney Creamer, Andrea Foster, Corey Lawrence, Jack McFarland,
Marjorie Schulz, Mark Waldrop
ccreamer@usgs.gov
2014-67003-22043

2. Importance of microbes & minerals for
stable carbon (C) formation
Cotrufo et al., 2015 Nature Geoscience
Underlying research question:
How does soil mineralogy
and microbial community
structure influence the
stability of C with different
chemistries across micro to
regional scales?

3. Activities span µm to km scales
Activity 1: Raman
spectroscopy development
Activity 2: Sterile and non-
sterile experiments
Activity 3: Soil
mesocosms
Activity 4: Climo-chronosequences
Repeat
Create
microbial
residues
Quantify
released
residues
Add plant-
derived
DOC
Activity 5:
Reactive
transport
modeling

4. Activities span µm to km scales
Activity 1: Raman
spectroscopy development
Activity 2: Sterile and non-
sterile experiments
Activity 4: Climo-chronosequences
13C organics

5. Controls on C stabilization
• Abiotic: Sorption,
aggregation
• Biotic: Efficiency of
microbial processing
• Influenced by C
chemistry, microbes,
mineralogy, soil
depth

6. Raman spectroscopy development
Non-destructive in-situ quantification of:
Microbial 13C assimilation
Carbon chemistry and spatial distribution

7. X X X X
X X
13C CO2
3 weeks
Does mineralogy affect stabilization of dead
microbial residues?
X X

8. Cumulative respiration
7.3%
0.73%
Anabolism
94% 13C
4% 13C
Dead microbes are stabilized on highly
sorptive minerals

9. C stabilization affected by mineral and life status
Aluminum
hydroxide:
Feldspar:
Live E. coli
Dead 13C
Arthrobacter
Live and dead
74%
58%
52%
0.8%

10. C stabilization affected by mineral and life status
Aluminum
hydroxide:
Feldspar:
Live E. coli
Dead 13C
Arthrobacter
Live and dead
52%
0.8%
25%
10%Live microbes
stabilized
residues
Live microbes
destabilized
sorbed residues

11. What is the fate of added C with depth?
• Glucose
– Efficient biotic
processing,
low sorption
• Oxalate
– Inefficient
processing,
high sorption
CarbonC/N
% Clay
SSA m2∙g-1
Soil specific surface area
(SSA) and % clay

12. Photo: Corey Lawrence
Construction of in
situ incubation units

13. Recovered in soil (%)
Oxalate-derived C not stabilized long-term
A
A/B
B
100806040200

14. Recovered in soil (%)
Glucose-derived C stabilized through profile
A
A/B
B
100806040200

15. Vulnerability of stabilized C with depth
-27%
-53%
-81%
A
A/B
B
100806040200
Recovered in soil (%)

16. Conclusions:
• Efficient biotic processing is an important driver of
the stabilization of added C
– Live microbes > dead residues
– Glucose > oxalic acid
• No simple rule for C stabilization on minerals
– Microbes can destabilize or stabilize C depending on
mineralogy
– Deep carbon was vulnerable to oxidation

17. Future directions
Activity 1: Raman
spectroscopy development
Activity 2: Sterile and non-
sterile experiments
Activity 3: Soil
mesocosms
Activity 4: Climo-chronosequences
Repeat
Create
microbial
residues
Quantify
released
residues
Add plant-
derived
DOC
Activity 5:
Reactive
transport
modeling

18. Future directions
Activity 1: Raman
spectroscopy development
Activity 2: Sterile and non-
sterile experiments
Activity 3: Soil
mesocosms
Activity 4: Climo-chronosequences
Repeat
Create
microbial
residues
Quantify
released
residues
Add plant-
derived
DOC
Activity 5:
Reactive
transport
modeling
• Raman applications:
• Generate parameters
for microbially explicit
models
• Extrapolation to larger
regions
• Mechanisms of C
stabilization and loss
• Applied questions on
land use change
• Increase soil carbon
and understanding
vulnerability

19. Thank you!
Tim Hyland and the Staff at
Wilder Ranch State Park
USGS Colleagues:
Marjorie Schulz
Sabrina Sevilgen
Sharon Mehlman
Andrea Foster
Funding:
USDA (2014-67003-22043)