Soil Inorganic Carbon and climate change in drylands? An emerging issue?

Chevallier T, Cournac L, Bernoux M, Cardinael R, Cozzi T, Girardin C, Chenu C

Soil Inorganic Carbon and climate change in drylands?

An emerging issue?

Soil Organic CarbonUnlocking the potential of mitigating and adapting to a changing climate

Theme 3. 3. Managing SOC in dryland soils

About 30 % of the Soil Organic Carbon are stored in dryland soils

In drylands

SOC

SIC

1583 Gt

946 Gt

68

32

916 Gt de SIC

431 Gt de SOC

Soil inorganic carbon ?

SOC

SIC

SIC kg m-2

8-64 kg m-2

Monger et al. 15, Geology

• SIC interacts with CO2 driven by biotic activities

• SOC and SIC evolution are likely link, (time scale ?)

CaCO3 + H2O + CO2

SIC are• CaCO3

• HCO3-

• H2CO3

• CO2

• Solid, in solution, gaz

Solid-solution-gaz equilibirum = f(pH, H20, pCO2, Ca2+, HCO3-)

Is SIC pool important to consider in

SOC studies in calcacerous soils ?

CaCO3 + 2H+ Ca2+ + CO2 + H2O

Ca2+ + 2 HCO3-

• Analyzing Soil Carbon , SOC and SIC and bulk densityContents and Stocks of SOC

Inorganic soil carbon, a methodological issue

• Dynamics of C contents and stocks Impact of climate change or land uses on SOC, SIC evolution…Does the CO2 measured come only from SOC decomposition ?

CO2 CO2

Stevendon and Verburg, 06, Bertrand et al. 07, Rovira and Vallejo 08, Inglima et al. 09, Ramnarine et al. 12, Tamir et al. 11, 12, Ahmad et al. 14, Chevallier et al. 16…

d13C of SIC about +2 à -11 ‰

d13C of SOC about -25 à -27 ‰ (C3 plants)

d13C of soil in between

d13C-CO2 = f d13CSIC + (1-f) d13CSOC

Carbon Isotopic measurements

d13Csoil = f d13CSIC + (1-f) d13CSOC

If no isotopic fractionations between

• SOC and CO2 (biological activities)

• CaCO3, HCO3-, CO2

Red reddish brown Cambisol

36% clay, 50% silt,14% sand, ; pH 8,9

22.1 g SOC kg-1 with 44.2 g SIC kg-1

20

40

30

50

4 incubation temperatures (°C) 28 days

Experimental settings

δ13CSOC = - 20.3 ± 4.4 ‰ δ13CSIC = - 4.1 ± 0.4 ‰

δ13Csoil = - 8.4 ± 0.4 ‰

Does temperature incubation

impact SOC and SIC dynamics ?

Mee

rman

s et a

l. 20

12

0-10

10-30

70-100

160-180Inter rowTree row

0 25 50 750

20

40

60

80

100

120

140

160

180

C content (g C kg-1 soil) -30 -25 -20 -15 -10 -5 0

d13C (‰)

20-10 gSOC kg-1

65 gSIC kg-1

Incubation at 20°C, 28 days

SIC

SOC in Tree rowSOC inter rowIs depth impact SOC and SIC

dynamic in a same way ?

Is there a correlation between

SOC and SIC dynamic ?

Results

10 20 30 40 50 60

-25

-20

-15

-10

-5

0

Temperature (°C)

d13 C

(‰

)

CO2 from soil (0-7 days)CO2 from soil (7-28 days)

SIC

SOC

-30 -25 -20 -15 -10 -5 00

20

40

60

80

100

120

140

160

180

d13C (‰)

Dept

h (c

m)

SIC

SOC in Tree rowSOC inter rowCO2 from soil

SIC and SOC contribute both to emitted CO2

d13CCO2 values higher with temperatures and depth

d13CCO2 between of d13CSIC and d13CSOC

Results

10 20 30 40 50 60

-25

-20

-15

-10

-5

0

Temperature (°C)

d13 C

(‰

)


SIC

SOC

-30 -25 -20 -15 -10 -5 00

20406080

100120140160180

d13C (‰)

Dep

th (

cm)

SIC


f = 0.20 – 0.24

f = 0.64

f = 0.2 – 0.1

f = 0.7- 0.3


SIC and SOC contributions to emitted CO2

Higher contribution of SIC to CO2 emissions with

temperatures and depth

Resultsd1

3 C (

‰)


SIC

SOC

SIC


10 20 30 40 50 60

-25

-20

-15

-10

-5

0

-30 -25 -20 -15 -10 -5 00

20

40

60

80

100

120

140

160

180

d13C (‰)

Dep

th (

cm)

Temperature (°C)

BUT If there is isotopic fractionation

between SIC and derived CO2 from SIC


SIC and SOC contributions to emitted CO2

Resultsd1

3 C (

‰)


SIC

SOC

SIC


10 20 30 40 50 60

-25

-20

-15

-10

-5

0

CO2 from SOC with isotopic fractionation

CO2 from SIC with isotopic fractionation-30 -25 -20 -15 -10 -5 0

0

20

40

60

80

100

120

140

160

180

d13C (‰)

Dep

th (

cm)

Temperature (°C)

BUT If there is isotopic fractionation

between SIC and derived CO2 from SIC

Resultsd1

3 C (

‰)


SIC

SOC

SIC


10 20 30 40 50 60

-25

-20

-15

-10

-5

0

CO2 from SOC with isotopic fractionation

CO2 from SIC with isotopic fractionation-30 -25 -20 -15 -10 -5 0

0

20

40

60

80

100

120

140

160

180

d13C (‰)

Dep

th (

cm)

Temperature (°C)

If there is isotopic fractionation

between SIC and derived CO2 from SIC,

SIC seems to contribute more than

100% to emitted CO2 !

Isotopic fractionation between SIC

and derived CO2 from SIC ?

How much and at what step ?

Results

L 0-10 cm

10-30 cm

70-100 cm

160-180 cm

0

100

200

300

400

500

600C-CO2 from SIC

C-CO2 from SOC

Tree row

f = 0.20

f = 0.64

20 30 40 500

200

400

600

800

1000

1200C-CO2 from SOC

C-CO2 from SIC

Incubation temperature (°C)

C-CO2 emissions (µg g-1 soil)

Calculated amounts of CO2 derived from SIC

and SOC are both stimulated by temperature

As amounts of CO2 emitted from SOC,

amounts of CO2 emitted from SIC in depth are low.

Amount of C-CO2 from SIC = f CO2d13C-CO2 = f d13CSIC + (1-f) d13CSOC


0-10 cm

Results

0

100

200

300

400

500

600

C-CO

2 em

issio

ns (µ

g g-

1 so

il)

L 0-10 cm

10-30 cm

70-100 cm

160-180 cm

0

100

200

300

400

500

600C-CO2 from SIC

C-CO2 from SOC

Inter rowTree row

f = 0.20

f = 0.64f = 0.24

20 30 40 500

200

400

600

800

1000

1200C-CO2 from SOC

C-CO2 from SIC

Incubation temperature (°C)


Calculated amounts of CO2 derived from SIC

and SOC are both stimulated by temperature

Amounts of CO2 emitted from SOC and SIC

are higher under Tree row than under Inter row.

Amount of C-CO2 from SIC = f CO2d13C-CO2 = f d13CSIC + (1-f) d13CSOC


0-10 cm 0-10 cm

19 gSOC kg-1 soil 11 gSOC kg-1 soil

Discussion 1. The main source of emitted CO2 is SOC decomposition

Total C-CO2 emissions µgC-CO2 g-1 soil

d13CCO2 (‰)

0 100 200 300 400 500 600 700 800

-25

-20

-15

-10

-5

0

40-50°C

Tunisian samplesFrench samples

0 100 200 300 400 500 600 700

-25

-20

-15

-10

-5

0

0-7 days7-28 days

Discussion

0 100 200 300 400 500 600 700 8000

100

200

300

400

500

f(x) = 0.1613967885811 x + 16.2905295692514R² = 0.924319397139957

C-CO2 from SIC, µgC-CO2 g-1 soil

C-CO2 from SOC, µgC-CO2 g-1 soil

40°C

50°C

1. The main source of emitted CO2 is SOC decomposition

2. CO2 derived from SIC and SOC are correlated

Total C-CO2 emissions µgC-CO2 g-1 soil

d13CCO2 (‰)

0 100 200 300 400 500 600 700 800

-25

-20

-15

-10

-5

0

40-50°C

Tunisian samplesFrench samples

0 100 200 300 400 500 600 700

-25

-20

-15

-10

-5

0

0-7 days7-28 days

Discussion

SIC SOC

d13CSIC d13CSOC

Total CO2 emissions

Isotopic exchanges



CO2 from SIC depends on SOC decomposition ?

Isotopic exchanges, CO2 from SIC could also comes

from SOC ?


Discussion

SIC SOC

d13CSIC d13CSOC

Total CO2 emissions

Isotopic exchanges



CO2 from SIC depends on SOC decomposition ?

Isotopic exchanges, CO2 from SIC came from SOC ?

d13CCO2 (‰)


At higher temperatures something

different happen, CO2 from SIC are

stimulated ?

CO2 derived from SIC and SOC are correlated

except at high temperatures.

Climate issueCO2 derived from SIC and SOC

are both stimulated by temperature

CO2 and 13CO2 measurements -Isotopic fractionation, isotopic exchanges, alkali traps,

time of incubation.

Other factors to measure (O2, Ca2+)

• SIC is not an inert C pool

• SIC contribute to CO2 emissions

Soil Inorganic Carbon and climate change in drylands?An emerging issue?

SIC is dynamic in short term incubations

Methodological issue

SIC and SOC dynamics with water content, irrigation ?

Soil Inorganic Carbon and climate change in drylands?

An emerging issue?

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Soil Inorganic Carbon and climate change in drylands? An emerging issue?

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