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

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?

Activities span µm to km scalesActivity 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

Activities span µm to km scalesActivity 1: Raman

spectroscopy development

Activity 2: Sterile and non-sterile experiments

Activity 4: Climo-chronosequences

13C organics

Controls on C stabilization• Abiotic: Sorption,

aggregation• Biotic: Efficiency of

microbial processing • Influenced by C

chemistry, microbes, mineralogy, soil depth

Raman spectroscopy development

Non-destructive in-situ quantification of:Microbial 13C assimilation

Carbon chemistry and spatial distribution

X X X X

X X

13C CO2

3 weeks

Does mineralogy affect stabilization of dead microbial

residues?

X X

Cumulative respiration

7.3%

0.73%

Anabolism94% 13C

4% 13C

Dead microbes are stabilized on highly sorptive minerals

C stabilization affected by mineral and life status

Aluminum hydroxide:

Feldspar:

Live E. coliDead 13C Arthrobacter

Live and dead

74%

58%

52%

0.8%

C stabilization affected by mineral and life status

Aluminum hydroxide:

Feldspar:

Live E. coliDead 13C Arthrobacter

Live and dead

52%

0.8%

25%

10%Live microbes stabilized residues

Live microbes destabilized sorbed residues

What is the fate of added C with depth?

• Glucose– Efficient biotic

processing, low sorption

• Oxalate– Inefficient

processing, high sorption

Carbon

C/N

% ClaySSA m2 g∙ -1

Soil specific surface area (SSA) and % clay

Photo: Corey Lawrence

Photo: Corey Lawrence

Construction of in situ

incubation units

Recovered in soil (%)

Oxalate-derived C not stabilized long-term

A

A/B

B

100806040200

Recovered in soil (%)

Glucose-derived C stabilized through profile

A

A/B

B

100806040200

Vulnerability of stabilized C with depth

-27%

-53%

-81%

A

A/B

B

100806040200Recovered in soil (%)

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

Future directionsActivity 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

Future directionsActivity 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

Thank you!Tim Hyland and the Staff

at Wilder Ranch State Park

USGS Colleagues:Marjorie Schulz

Sabrina SevilgenSharon Mehlman

Andrea FosterFunding:

USDA (2014-67003-22043)