Prairies, séquestration du carbone et effet de serre

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Prairies, séquestration du carbone et effet de serre

Jean-François Soussana

To cite this version:

Jean-François Soussana. Prairies, séquestration du carbone et effet de serre. Séminaire Franco-

Britannique, MAP, Jun 2009, Paris, France. 6 p. �hal-02813389�

Séminaire Franco-Britannique 17 Juin 2009

A L I M E N T A T I O N A G R I C U L T U R E

E N V I R O N N E M E N T

Prairies, séquestration du carbone et effet de serre

Jean-François Soussana Unité de Recherche sur l’Ecosystème Prairial,

INRA, Clermont-Ferrand

Outline

1. Carbon sequestration in European grasslands

2. C sequestration in the context of greenhouse gas balance

3. Vulnerability of carbon stocks to climate change and biodiversity loss

Mt C year^-1

-600 -400 -200 0 200 400 600

Peatlands Grasslands Croplands Woodlands Forests

Estimated carbon sink: 7-11 % of fossil fuel emissions

Uncertainties in the land carbon balance of Europe

(Janssens et al. Science, 2003) .

Source Sink

370 Mt CO

yr

The eddy covariance method for measuring CO ₂ fluxes

[CO ₂ ] = C’

Vertical wind = w’ CO ₂ flux = w’ c’

Flux towers : Spatial scale ≈ 1 km ²

C fluxes in a grassland ecosystem

NCS = (F

- F

- F

- F

) + (F

- F

- F

) - (F

+ F

) Simplified balance in a temperate managed system:

NCS = (F

- F

) + (F

- F

– F

) – F

(Soussana and Tallec, 2009, Animal, in press) FCH4

FCO2

Fleach

Fanimal-products

Fmanure

Fharvest

Ferosion

Ffire

FVOC

Net carbon storage FCH4

FCO2

Fleach

Fanimal-products

Fmanure

Fharvest

Ferosion

Ffire

FVOC

Net carbon storage (NCS)

C sequestration (NCS) at grazed only European sites (g C m ^-2 yr ^-1 )

NCS = 129

F_leach 10

F_CH4

4 145

Fanimal-products 2

Attributed NCS = 129 F_CO2

Mean of 2 sites (Soussana et al., 2007, AGEE; Soussana & Tallec, 2009, Animal)

C sequestration (NCS) at cut European sites

(g C m ^-2 yr ^-1 )

?

0 100 20 0 3 00 400 500 600 700 800

Carbon balance (gCCm-2 yr-1) -600

-400

-200

0

200

400 B G

B G B S

B S

C A

C A Lai

Lae Lai

Lae LE

M A

M A

O ei O e i

O ee O E e

- -

• The less carbon is used, the more is returned to the soil, which increases C sequestration

• Nitrogen supply also favours carbon sequestration

Carbon sequestration (NCS) at 10 European grassland sites

(Soussana et al. Agriculture, Ecosys. Environment, 2007)

Carbon gain

Carbon loss

Fate of harvested C at cut sites (g C m ^-2 yr ^-1 )

Mean of 3 sites (Soussana et al., 2007, AGEE; Soussana & Tallec, 2009, Animal)

Fleach 10 Fmanure

F_harvest 323 370

34 NCS =71

34 113

NCS@barn = 28

Attributed NCS = 99

At barn F_CO2

Fmanure@barn F_CO2@barn

F_CH4@barn 13 132

Fanimal-products@barn

65 51

Flabile C losses

Att-NCS = NCS + NCS

= NCS + f

Max[0, (1–f

)F

- F

]

Fate of harvested C at cut and grazed sites (g C m ^-2 yr ^-1 )

Att-NCS = NCS + NCS

= NCS + f

Max[0, (1–f

)F

- F

]

F_leach 10 NCS = 50

F_harvest

At barn

237 Fmanure@barn

17 83

NCS@barn = 23

Attributed NCS = 73 5

F_CH4 F_CO2

290

17 Fmanure

F_CO2@barn F_CH4@barn

9 98 Fanimal-products

5

Fanimal-products@barn

47 43 Flabile C losses

Mean of 4 sites (Soussana et al., 2007, AGEE; Soussana & Tallec, 2009, Animal)

Land carbon sink distribution in Northern America

(Peters et al. 2007, PNAS)

Land carbon sink in Northern America

(Peters et al., 2007, PNAS)

Outline

• Carbon sequestration in European grasslands

• C sequestration in the context of GHG balance

• Vulnerability of carbon stocks to climate change and biodiversity loss

Herbivore

Vegetation

Soil

Atmosphere

CH

CO

CO

CH

CO

N

O

Greenhouse gas and organic carbon fluxes in a grassland

Manure / Slurry Organic carbon

Dissolved organic C Hay / Silage

Greenhouse

Greenhouse gas gas balance of balance of 10 10 European

European grassland grassland sites sites

Capsule SF6 SF6 CH4

CH

et SF

SF6

CH4 SF6 CH4 SF

CH4

CH

et SF

CH

and SF

H

4

CH

: in-situ dual tracer mehod - ^N

O: automated chambers On site emissions of N

O and CH

, converted in CO

equivalents using the GWP of each gas, offset 43 % of the ecosystem C sink

The net greenhouse gas balance, also including off-site emissions of N

O and CH

through digestion of cut herbage, is a small net sink by 85 ± 77 g C m

yr

(Flechard et al., 2007, Pinares-Pineiro et al., 2007, Soussana et al., 2007)

GHG balance in CO ₂ equivalents at European sites

(g CO ₂ -C equivalents m ^-2 yr ^-1 )

(Soussana et al., 2007, Soussana and Tallec, 2009) Management NCS Att-

NCS

Grazing 471 471

Grazing &

cutting

183 268

Cutting 259 359

NGHG Att- NGHG

320 320 -22 -272 230 -141

NGHG: grassland greenhouse gas balance

Att-NGH: attributed greenhouse gas balance (including off site emissions)

The GHG balance of the agriculture sector in Europe

Grassland C sequestration would play a significant role for the European agriculture sector

GHG balance of agriculture in EU25 including C sequestration

Tg C yr^-1

-40 -20 0 20 40 60 80

Grassland Cropland Undisturbed peat Drained peat CH4 N2O

(Schulze et al., submitted to Nature Geosciences)

Outline

1. Carbon sequestration in European grasslands

2. C sequestration in the context of GHG balance

3. Vulnerability of carbon stocks to climate change and biodiversity loss

Impacts of climate variability and extremes on the C cycle in grasslands

Interannual variability

Agricultural

management Greenhouse gas emissions

Climate change impact on grassland soil carbon sequestration

(Smith et al., 2005, Global Change Biol.)

Biodiversity loss may impact C sequestration

Soil organic matter

CO ₂

Energy

Chemical characteristics of litter

Plant Production/

Allocation

Micro- environmental

Moisture

Plant species diversity Plant functional traits

Defoliation by cutting and grazing

Concluding remarks

• There is a clear potential for C sequestration in European grasslands

• An internationally agreed methodology is still missing to develop mitigation options in the livestock sector based on C sequestration

• Reducing CH ₄ and N ₂ O emissions from the livestock sector is strongly needed, given that soil carbon sequestration is reversible and vulnerable to climate change and biodiversity loss

• Mitigation strategies could be based on the net GHG balance of livestock farms

Thank you