Ecosystem componentActivity 1.6

Grasslands and wetlands

Jean-François SoussanaKatja Klumpp, Nicolas Vuichard

INRA, Clermont-Ferrand, France

CarboEurope, Poznan meeting, October 9, 2007.

Climate drivers of grassland and wetland annual GPP at CarboEurope

IP sites

(n=50, r2=0.705, P<0.0001)

Log(GPP) = 2.27 + 0.377. Log (Temp) + 0.614. Log (Precip)

Interannual variability of GPP in grasslands

(preliminary analysis based on FluxNet)

(n=37, r2 =0.235, P<0.01)

Grassland primary productivity is highly sensitive to rainfall variabilityNo significant relationship for other ecosystem types (except EB forests)

Water Use Efficiency control by LAI

In a sparse vegetation, evaporation from the soil is the major avenue of water lossLow precipitation reduces LAI and, hence, WUE...

Low WUE further reduces primary productivity.

(C Beer et al., unpub.)

Mean C fluxes (gC m-2 yr-1) at CarboEurope grassland and wetland

sites

NBP = K2 (K1 GPP – Cut – Digest . Intake + Manure)– K3 e LN(Q10).Tsoil/10 –FCH4-C

(n=43, R2=0.52, P<0.001)

(Soussana et al., unpub.)

GPP1228

NBP128

Rauto.

615Rhetero.Litter 294

Rhetero.Herbivore 46

Rhetero.SOM 89

Cut75

Intake70

Manure16

K1=0.50 K2=0.43

K3 = 83Q10 =1.21Digest.=0.65

Enteric fermentation3.4

Fate of NPP and manure (at C sink sites)

CutCut & GrazedGrazedAbandoned & Wet

Role of grazing and cutting management for NBP

-300

-200

-100

0

100

200

300

400

500

400600

8001000

12001400

16001800

20002200

0100

200300

400500

NB

P (

g C

m y

r-1)

GPP

(g C

m-2 y

r-1 )

Cuts (gC m -2 yr -1

)

Cutting only, no manure

-300 -200 -100 0 100 200 300 400 500

GPP vs Max_cutting vs NBP_max_cutting

-300

-200

-100

0

100

200

300

400

500

400600

8001000

12001400

16001800

20002200

0100

200300

400500

NB

P (

g C

m y

r-1)

GPP

(g C

m-2 y

r-1 )

Intake (gC m -2 yr -1

)

Grazing only, no manure

-300 -200 -100 0 100 200 300 400 500

-300

-200

-100

0

100

200

300

400

500

400

600800

10001200

14001600

18002000

2200

0100

200300

400500

NB

P (

g C

m y

r-1)

GPP

(g C

m-2 y

r-1 )

Intake (gC m -2 yr -1

)

Grazing only, no manure

-300 -200 -100 0 100 200 300 400 500

GPP vs Max_grazing vs NBP0

-300

-200

-100

0

100

200

300

400

500

400

600800

10001200

14001600

18002000

2200

0100

200300

400500

NB

P (

g C

m y

r-1)

GPP

(g C

m-2 y

r-1 )

Cuts (gC m -2 yr -1

)

Cutting only, no manure

-300 -200 -100 0 100 200 300 400 500

GPP vs Max_cutting vs NBP_max_cutting

Maximalgrazing

Maximalcutting

Current herbage utilisation is lower than maximum

Maximal grazingMaximal cuttingGrazing and cutting at managed grassland sites

Herbivore

Vegetation

Soil

Atmosphere

CH4

CO2

CO2

CH4

CO2

N2O

Greenhouse gas and organic matter fluxes in a grassland

Manure / Slurry

OM fluxes

Dissolved organic C

Hay / Silage

On site GHG balance in CO2-C equivalents (g CO2-C m-2 yr-1)

GPP1228

GHG90

Rauto.

615Rhetero.Litter 294

Rhetero.Herbivore 46

Rhetero.SOM 89

Cut75

Intake70

Manure16

K1=0.50 K2=0.43

K3 = 83Q10 =1.21Digest.=0.65

CH4 (Enteric Fermentation)27

N2O emission14

On site GHG balance in CO2-C equivalents is on average 70 % of NBP

Total GHG balance in CO2-C equivalents (g CO2-C m-2 yr-1)

GPP1228

GHG 70

Rauto.

615Rhetero.Litter 294

Rhetero.Herbivore 46+45

Rhetero.SOM 89

Cut

Intake

Manure

K1=0.50 K2=0.43

K3 = 83Q10 =1.21Digest.=0.65

CH4 (Enteric Fermentation)27+24

N2O emission14+26

Total GHG balance in COTotal GHG balance in CO22-C equivalents is on average 55 % of NBP.-C equivalents is on average 55 % of NBP.

Upscaling method based on annual means

PrecipitationAir temperatureSoil temperature

GPP

ManureCutIntake

NBP N fertiliser supply

N2OCH4CO2

GHG balance

Spatial distribution of NBP of grasslands in Europe (data

upscaling)

Assuming a management similar to mean site management

C sequestration efficiency in grasslands (data upscaling)

Assuming a management similar to mean site management

How large is the grassland C sink?

Estimates of European grassland C flux during the 1990s

-160

-140

-120

-100

-80

-60

-40

-20

0

Janssens et al.(2003)

Janssens et al.(2005)

Smith et al.(2005)

CarboEurope(data upscaling)

Study and year

Sin

k o

f C

fro

m g

ras

sla

nd

s

(Mt

C y

r-1)

Impacts of climate variability and extremes on the C cycle in

grasslandsInterannual variability

Agricultural management

Biogeochemicalcycles

Separating spatial and interannual variability of fluxes

Climate driver

Flu

xLong-term mean

Individual year

Spatial variability

Interannual variability

Interannual variability of GPP at CarboEurope IP sites grasslands

Grasslands and wetlands worldwide:

GPP, site years(preliminary analysis of Fluxnet data)

n=44, r2=0.59, P<0.001

n=44, r2=0.49, P<0.001

Grasslands and wetlands worldwide

NEE, site years(preliminary analysis of Fluxnet data)

Spatial and interannual variability of evapotranspiration

(preliminary analysis based on FluxNet)

Spatial variability Interannual variability

Slopes between sites and between years are not significantly different

Interannual variability of GPP in grasslands

(preliminary analysis based on FluxNet)

(n=37, r2 =0.235, P<0.01)

Grassland primary productivity is highly sensitive to rainfall variabilityNo significant relationship for other ecosystem types (except EB forests)

Spatial variability of GPP in grasslands (preliminary analysis based on FluxNet)

(n=20, Adj. r2= 0.14; P<0.10)

Precipitation (mm)

500 1000 1500 2000

GP

P (

gC m

-2 y

r-1)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Slopes of variability between sites and between years are similarNo significant role of ecosystem acclimation to mean climate?

Water Use Efficiency control by LAI

In a sparse vegetation, evaporation from the soil is the major avenue of water lossLow precipitation reduces LAI and, hence, WUE...

Low WUE further reduces primary productivity.

(C Beer et al., unpub.)

Water Use Efficiency control by LAI

In a sparse vegetation, evaporation from the soil is the major avenue of water lossLow precipitation reduces LAI and, hence, WUE...

Low WUE further reduces primary productivity.

(C Beer et al., unpub.)

Climateradiation

precipitationtemperature

pressurewind speed

Soiltexture

porosityconductivitybulk density

depth of lower boundary

Managementcutting dates

N-application datesN-amount

stocking rateclover fraction

PaSimEcosystem processes

CO2 flux

N2O flux

CH4 flux

GWP

Energy fluxes

Biomass

C & N stocks

etc

PASIM model

Cut/Graz site 2002 2003 2004 2005

C CH-Oens x x x

C DE-Grillenburg x x x

C ES-VAD x x

C F-Laq-ext x x x

C F-Laq-int x x x

C IE-Carlow x x

C/G IT-MtBondone x x

G IE-Dripsey x x

G IT-Amperlo x x

G PT -Mitra x x

G UK-Easterbush x x

10 european sites were simulated

PASIM model assesment with GPP and Reco (kg C m-2 yr-1)

Spin-up runs with site field management

Reco is overestimated at grazed sites: - Soils are apart from equilibrium (soil C sink),- Need to add a transient correction of slow C pools? (see Wuzler & Reichstein, 2007)

Grazedsites

Simulation of europeen grassland sites with PaSim

The impact of ecological factors - site history - temperature- precipitation- management (stocking rate, cutting frequence, N-supply)

on green house-gas-emissions and C storage

Actual management

CutGrazed

Automated management without N-supply

Automated CutAutomated Grazed

Simulations with automated management

Automated management withN-supply

Automated Cut+NAutomated Grazed+N

Intensification

Management change

Current site

management

Automated

management

NBP

-N

NBP

+N

C C 0.04 0.12

C G -0.01 0.28

G C -0.03 0.06

G G -0.38 -0.44

Change in management: role of grazing

Cut =C

Grazing = G

(in kg C m-2 yr-1)

Shifting to grazing, according to model, would increase net C storage

Shifting from cuttingto grazing increases C storage

+

+ +

Synthesis paper

• First draft will be discussed during grassland & wetland session

• Conclusions: grasslands are a strong C sink (ca. same as forests)

• Trade-off by N2O and CH4 is relatively low (30 % reduction in NBP)

• Indirect emissions (e.g. indirect N2O, off site forage digestion) further reduce NBP by 15 %

• The C sink can be managed, but it is highly vulnerable to drought events and, hence, to climate change.

Next steps

• Upscaling using agricultural statistics (livestock density, grazing type, N fertiliser amounts)

• Show that increased herbage utilisation (the livestock footprint) reduces the sink size.

• Run PASIM since 1900 and test the role of global change (CO2, warming, N deposition..) and management change drivers for the grassland and wetland C balance

• Discuss where does the C go ? – Deep soil C (not surveyed but close to 2/3 of total in deep soils) – Is deep soil C stable without energy supply (see C-N session,

Fontaine et al.) Does its accumulation saturate?

Advertisement for grassland & wetland parallel session

- Summary of wetland workshop- Synthesis of results on grasslands and

wetlands(Discussion based on a first draft )

- Modelling- Plant functional traits: first results and

discussion - Other papers to be prepared