Ecosystem component Activity 1.6 Grasslands and wetlands

1. CarboEurope, Poznan meeting, October 9, 2007. Ecosystem componentActivity 1.6Grasslands and wetlands Jean-François Soussana Katja Klumpp, Nicolas Vuichard INRA, Clermont-Ferrand, France

2. Climate drivers of grassland and wetland annual GPP at CarboEurope IP sites Log(GPP) = 2.27 + 0.377. Log (Temp) + 0.614. Log (Precip) (n=50, r2=0.705, P<0.0001)

3. Separating spatial and interannual variability of fluxes Long-term mean Individual year Interannual variability Flux Spatial variability Climate driver

4. Interannual variability of GPP at CarboEurope IP sites grasslands

5. 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 variability No significant relationship for other ecosystem types (except EB forests)

6. Water Use Efficiency control by LAI (C Beer et al., unpub.) In a sparse vegetation, evaporation from the soil is the major avenue of water loss Low precipitation reduces LAI and, hence, WUE... Low WUE further reduces primary productivity.

7. Rhetero. Herbivore 46 Rhetero. SOM 89 Rhetero. Litter 294 GPP 1228 Rauto. 615 K3 = 83 Q10 =1.21 K1=0.50 K2=0.43 Digest.=0.65 NBP 128 Intake 70 Enteric fermentation 3.4 Cut 75 Manure 16 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.)

8. Fate of NPP and manure (at C sink sites) Cut Cut & Grazed Grazed Abandoned & Wet

9. Role of grazing and cutting management for NBP Maximal grazing Maximal cutting

10. Current herbage utilisation is lower than maximum

11. Greenhouse gas and organic matter fluxes in a grassland OM fluxes Hay / Silage Atmosphere Manure / Slurry Dissolved organic C CH4 CO2 Herbivore CO2 Vegetation CH4 CO2 N2O Soil

12. N2O emission 14 Rhetero. Herbivore 46 Rhetero. SOM 89 Rhetero. Litter 294 GPP 1228 Rauto. 615 K3 = 83 Q10 =1.21 K1=0.50 K2=0.43 Digest.=0.65 GHG 90 Intake 70 CH4 (Enteric Fermentation) 27 Cut 75 Manure 16 On site GHG balance in CO2-C equivalents (g CO2-C m-2 yr-1) On site GHG balance in CO2-C equivalents is on average 70 % of NBP

13. Total GHG balance in CO2-C equivalents (g CO2-C m-2 yr-1) N2O emission 14+26 Rhetero. Herbivore 46+45 Rhetero. SOM 89 Rhetero. Litter 294 GPP 1228 Rauto. 615 K3 = 83 Q10 =1.21 K1=0.50 K2=0.43 Digest.=0.65 GHG 70 Intake Cut Manure CH4 (Enteric Fermentation) 27+24 Total GHG balance in CO2-C equivalents is on average 55 % of NBP.

14. Upscaling method based on annual means Precipitation Air temperature Soil temperature GPP Manure Cut Intake NBP N fertiliser supply CH4 CO2 N2O GHG balance

15. Spatial distribution of NBP of grasslands in Europe (data upscaling) Assuming a management similar to mean site management

16. C sequestration efficiency in grasslands (data upscaling) Assuming a management similar to mean site management

17. How large is the grassland C sink?

18. PASIM model

19. 10 european sites were simulated

20. PASIM model assesment with GPP and Reco (kg C m-2 yr-1) Spin-up runs with site field management Grazed sites 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)

21. 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

22. Intensification Management change Simulations with automated management Actual management Cut Grazed Automated management withoutN-supply Automated Cut Automated Grazed Automated management with N-supply Automated Cut+N Automated Grazed+N

23. + Shifting from cutting to grazing increases C storage + + Change in management: role of grazing (in kg C m-2 yr-1) Cut =C Grazing = G Shifting to grazing, according to model, would increase net C storage

24. 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.

25. 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?

26. Interannual variability Agricultural management Biogeochemical cycles Impacts of climate variability and extremes on the C cycle in grasslands

27. 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