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Grasslands: NBP, NPP and GPP

CarboEurope, Poznan meeting, October 9, 2007. Grasslands: NBP, NPP and GPP. Jean-François Soussana Katja Klumpp, Nicolas Vuichard INRA, Clermont-Ferrand, France. Uncertainty in calculation of NPP in grasslands (Lauenroth et al., 2006).

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Grasslands: NBP, NPP and GPP

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  1. CarboEurope, Poznan meeting, October 9, 2007. Grasslands: NBP, NPP and GPP Jean-François Soussana Katja Klumpp, Nicolas Vuichard INRA, Clermont-Ferrand, France

  2. Uncertainty in calculation of NPP in grasslands(Lauenroth et al., 2006)

  3. Coefficient of variation of above and below ground NPP with 6 methods

  4. No way to estimate acurately NPP from biomass increments !

  5. New C buildup and old C decay Cold = a e -k t Cnew = a’ (1 – e –k’ t) (Klumpp et al. 2007, Biogeosciences)

  6. C turnover belowground (>200 µ) (Klumpp et al. 2007, Biogeosciences)

  7. Rate of C deposition Cnew = a’ (1 – e –k’t) For t -> 0, initial slope : dCnew/dt = k’ a’ = 0.45 (mg C g soil month-1) Initial slope represents the below-ground C deposition (not including fastly respired exudates) When integrated over total soil gives the below-ground NPP: First estimate: BNPP 78 g C m-2 month-1during spring-summer ANPP: 200 gC m-2 month-1 NPP = 278 gC m-2 month-1 GPP was 600 gC m-2 month-1 (Klumpp et al. 2007, AGEE) NPP/GPP = 0.46 (first cut, needs checks on deep soil layers)

  8. 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.)

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

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

  11. Current herbage utilisation is lower than maximum

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