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

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

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

4. Interannual variability of GPP at CarboEurope IP sites grasslands

5. Interannual variability of GPP in grasslands (preliminary analysis based on FluxNet) (n=37, r 2 =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 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. (C Beer et al., unpub.)

7. Mean C fluxes (gC m -2 yr -1 ) at CarboEurope grassland and wetland sites NBP = K 2 (K 1 GPP – Cut – Digest. Intake + Manure)– K 3 e LN(Q10).Tsoil/10 –F CH4-C (n=43, R 2 =0.52, P<0.001) (Soussana et al., unpub.) GPP 1228 NBP 128 R auto. 615 R hetero. Litter 294 R hetero. Herbivore 46 R hetero. SOM 89 Cut 75 Intake 70 Manure 16 K 1 =0.50K 2 =0.43 K 3 = 83 Q 10 =1.21 Digest.=0.65 Enteric fermentation 3.4

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. Herbivore Vegetation Soil Atmosphere CH 4 CO 2 CH 4 CO 2 N2ON2O Greenhouse gas and organic matter fluxes in a grassland Manure / Slurry OM fluxes Dissolved organic C Hay / Silage

12. On site GHG balance in CO 2 -C equivalents (g CO 2 -C m-2 yr -1 ) GPP 1228 GHG 90 R auto. 615 R hetero. Litter 294 R hetero. Herbivore 46 R hetero. SOM 89 Cut 75 Intake 70 Manure 16 K 1 =0.50K 2 =0.43 K 3 = 83 Q 10 =1.21 Digest.=0.65 CH 4 (Enteric Fermentation) 27 N 2 O emission 14 On site GHG balance in CO 2 -C equivalents is on average 70 % of NBP

13. Total GHG balance in CO 2 -C equivalents (g CO 2 -C m-2 yr -1 ) GPP 1228 GHG 70 R auto. 615 R hetero. Litter 294 R hetero. Herbivore 46+45 R hetero. SOM 89 Cut Intake Manure K 1 =0.50K 2 =0.43 K 3 = 83 Q 10 =1.21 Digest.=0.65 CH 4 (Enteric Fermentation) 27+24 N 2 O emission 14+26 Total GHG balance in CO 2 -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 N2ON2O CH 4 CO 2 GHG balance

15. Grassland GPP over Europe Data upscaling PASIM model (Vuichard et al., 2007 GBC)

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

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

18. How large is the grassland C sink?

19. PASIM model

20. Cut/Grazsite2002200320042005 CCH-Oensxxx CDE-Grillenburgxxx CES-VADxx CF-Laq-extxxx CF-Laq-intxxx CIE-Carlowxx C/GIT-MtBondonexx GIE-Dripseyxx GIT-Amperloxx GPT -Mitraxx GUK-Easterbushxx 10 european sites were simulated

21. 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) Grazed sites

22. 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

23. Actual management Cut Grazed Automated management without N-supply Automated Cut Automated Grazed Simulations with automated management Automated management with N-supply Automated Cut+N Automated Grazed+N Intensification Management change

24. Current site management Automated management NBP -N NBP +N CC0.040.12 CG-0.010.28 GC-0.030.06 GG-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 cutting to grazing increases C storage + + +

25. Role of management: measurements vs. modelling With PaSim NBP = 0.68 (0.58 GPP – Cut – 0.65. Intake + Manure)– 125 e LN(2).Tsoil/10 –F CH4-C (R 2 =0.1) NBP = 0.44 (0.5 GPP – Cut – 0.65. Intake + Manure)– 81 e LN(1.2).Tsoil/10 –F CH4-C (n=43, R 2 =0.52, P<0.001)

26. 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 N 2 O and CH 4 is relatively low (30 % reduction in NBP) Indirect emissions (e.g. indirect N 2 O, 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.

27. 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 (CO 2, 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?

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

29. 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