Outline. Modelling C sequestration in grasslands. in the context of a full greenhouse gas inventory. 1. Carbon sequestration in European grasslands

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1 C sequestration workshop, FAO, Rome, April 29 Modelling C sequestration in grasslands in the context of a full greenhouse gas inventory Outline 1. Carbon sequestration in European grasslands Jean-François Soussana INRA, Clermont-Ferrand, France 2. C sequestration in the context of H balance 3. Vulnerability of carbon stocks to climate change and biodiversity loss Uncertainties in the carbon balance of European ecosystems (Janssens et al. Science, 23). The eddy covariance method for measuring CO 2 fluxes Forests oodlands Source Sink [CO 2 ] = C Vertical wind = w CO 2 flux = w c Croplands rasslands 37 Mt CO 2 yr -1 Peatlands eographic Europe Mt C year -1 Fossil fuel emissions = 185 Mt C per year Flux towers : Spatial scale 1 km 2 1

2 C fluxes in a grassland ecosystem C fluxes at grazed only European sites (g C m -2 yr -1 ) F fire F CO2 F CH4 F VOC F CO2 F CH4 F manure F harvest F animal-products F animal-products Net carbon storage F leach F erosion NCS = 129 NCS = (F CO2 -F CH4-C -F VOC -F fire ) + (F manure -F harvest -F animal-products ) - (F leach + F erosion ) Simplified balance in a temperate managed system: NCS = (F CO2 -F CH4-C ) + (F manure -F harvest F animal-products ) F leach (Soussana and Tallec, 29, Animal, in press) 1 F leach Attributed NCS = 129 (Soussana et al., 27, AEE, Soussana and Tallec, 29 (Animal, in press) Mean of 2 sites ( C fluxes at cut only European sites (g C m -2 yr -1 ) At barn C fluxes at grazed and cut European sites (g C m -2 yr -1 ) At barn F CO2 F F animal-products@barn F CO2 F CH4 F animal-products F F animal-products@barn F manure 37 F harvest 323 F F labile C losses F 51 manure@barn F harvest 237 F F labile C losses F 43 manure@barn F manure NCS =71 NCS@barn = 28 NCS = 5 NCS@barn = 23 1 F leach Attributed NCS = 99 1 Attributed NCS = 73 F leach Att-NCS = NCS + = NCS + f humif Max[, (1 f diges )F harvest -F manure ] Soussana et al., 27, AEE Soussana and Tallec, 29 (Animal, in press) Mean of 3 sites Att-NCS = NCS + = NCS + f humif Max[, (1 f diges )F harvest -F manure ] (Soussana et al., 27, AEE) Mean of 4 sites 2

3 Carbon sequestration at 1 European grassland sites -6-4 MA Carbon gain Modelling equilibrium C stocks in Europe PASIM model (complex model, spin-up run) Carbon balance (gccm -2 yr -1 ) -2 B B MA BS Lae Lae Oei Lai LE Lai OEe BS CA Oei - - Oee 2 Carbon loss Herbage utilisation by grazing and cutting (gc m -2 an -1 ) CA The less carbon is used, the more is returned to the soil, which increases C sequestration Nitrogen supply also favours carbon sequestration (Soussana et al. Agriculture, Ecosys. Environment, 27) Assuming optimal grazing and cutting management N supply from fertilizer statistics (Vuichard et al. 27, lobal Biochem. Cycles) f(p) Fitted temperature and precipitation response functions of soil respiration P (mm) f(t) Ea=35K POM Ea=45K SOM Tair (Lloyd and Taylor, 1994 ; Reichstein et al., 26) A maximum rate of herbage use for carbon sequestration Fraction of photosynthesis utilised at 7 C soil temperature Carbon sequestration Cut razed PP (gc m -2 yr -1 ) 3

4 Outline reenhouse gas and organic carbon fluxes in a grassland Carbon sequestration in European grasslands Organic carbon Herbivore CH 4 CO 2 C sequestration in the context of H balance Hay / Silage CO 2 Atmosphere Vegetation CH 4 Vulnerability of carbon stocks to climate change and biodiversity loss Manure / Slurry CO 2 N 2 O Dissolved organic C Soil reenhouse gas balance of 1 European grassland sites Budgeting H: Net H balance in CO 2 equivalents H CH4 SF6 6 Capsule SF6 CH 4 et and SF SF 66 4 CH 4 : in-situ dual - tracer mehod N 2O: automated chambers On site emissions of N 2 O and CH 4, converted in CO 2 equivalents using the P of each gas, offset 43 % of the ecosystem C sink The net greenhouse gas balance, also including off-site emissions of N 2 O and CH 4 through digestion of cut herbage, is a small net sink by 85 ± 77 g C m -2 yr -1 (Flechard et al., 27, Pinares-Pineiro et al., 27, Soussana et al., 27) Net exchange rate in CO 2 equivalents (NH, g CO 2 /m 2 per year), using the global warming potential (P) of each gas at the 1 years time horizon (IPCC, 27): NH = k CO2 (NCS + F CH4-C ) - P CH4 F CH4 -P N2O F N2O, where k CO2 = 44/12 g CO 2 gc, F CH4, is the methane emission (g CH 4 /m 2 per year) and F N2O is the nitrous oxide emission (g N 2 O/m 2 per year). CH 4 is not double counted as CO 2 in equation 4, since F CH4-C is added to NCS. (Soussana and Tallec, 29) 4

5 Budgeting H: Attributed H balance in CO 2 equivalents H balance in CO 2 equivalents at European sites (g CO 2 -C m -2 yr -1 ) Att-NH= k CO2 (Att-NCS+F CH4-C )- P CH4 (F CH4 +f CH4 f digest F harvest )- P N2O F N2O Management NCS Att- NCS rassland methane PCH4FCH4 Total methane PCH4FCH4 rassland N2O PN2OFN2O NH Att- NH, where f CH4 is the fraction of the digested C in the barn which is emitted as CH 4 through enteric fermentation. razing razing & cutting Cutting (Soussana and Tallec, 29) (Soussana et al., 27, Soussana and Tallec, 29) The H balance of the agriculture sector in Europe Outline Carbon- rasslands Carbon- Croplands 1. Carbon sequestration in European grasslands N2O CH4 2. C sequestration in the context of H balance Mt CO2 year -1 rassland C sequestration would play a significant role for the European agriculture sector 3. Vulnerability of carbon stocks to climate change and biodiversity loss 5

6 Impacts of climate variability and extremes on the C cycle in grasslands rassland and wetland carbon fluxes are controlled by annual precipitation Interannual variability Agricultural management reenhouse gas emissions Annual PP (gc m -2 yr -1 ) Photosynthesis n=44, r 2 =.59, P<.1 Annual Net Ecosystem Exchange (gc m -2 yr -1 ) Net CO 2 exchange Annual precipitation (mm) Annual precipitation (mm) (FLUXNET data) Climate change impact on grassland soil carbon sequestration Biodiversity loss may impact C sequestration Plant species diversity Plant functional traits Energy CO 2 Plant Production/ Allocation Chemical characteristics of litter Defoliation by cutting and grazing Soil organic matter Moisture Temperature Microenvironmental (Smith et al., 25, lobal Change Biol.) 6

7 Biodiversity effect at patch scale in managed grasslands Plant species richness and root traits affect C sequestration in model grasslands 4 3 Overall r² =.51 *** (A) 2 1 AB r² =.58 ** MU r² =.48 * MF r² =.61 ** Number of Species (ross et al., in revision, BAE) At low simulated grazing, carbon sequestration increased with plant species diversity Simulated grazing controlled the balance between competitive and conservative plant types The dominance of conservative plant types with coarse roots increased carbon sequestration and reduced herbage production. (Klumpp et al., Biogeosciences 27 Klumpp et al., AEE, 27) Root traits effects on productivity and C sequestration C flux (g C m -2 yr -1 ) ANPP Direct effect LL Trait LH LH HH log(sl) (m g -1 DM) BNCS LL LH HH HL Concluding remarks Mitigation strategies could be based on the net H balance of livestock farms 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 vulnerable to climate change and biodiversity loss (Klumpp and Soussana, 29 CB, in press) 7

8 Thank you 8