Carbon sink activity of managed grasslands - CO 2 fluxes and SOC changes

Transcription

1 Carbon sink activity of managed grasslands - CO 2 fluxes and SOC changes K. Klumpp, F. Gastal, A. Chabbi, N. Senapati, C. de Berranger, X. Charrier, O. Darsonville, N. Mascher

2 Potentiel d atténuation des GES des Prairie la surface importante qu elles occupent Prairie permanent ( ) Ecosystème Forêt Prairies Cultures Surface (ha) % 15 M 15 M 15 M leur potentiel de stockage de C par ha NUTS 2 (Smit et al 2008) Drawn from data in Smith et al., 2007a.

3 Quels sont les modes de gestion de la prairie (intensification, mode d exploitation) les plus favorables au stockage du carbone? Quels sont les facteurs les plus favorables (gestion vs climat) Démarche : Système d observation et manipulation Suivi de l évolution des stocks de carbone Bilans de carbone à partir de l intégration des flux de CO 2

4 SOERE-ACBB Le Système d Observation et de Recherche en Environnement «Agroécosystèmes Cycles Biogéochimiques et Biodiversité» Picardie Mons-en-Chaussée Cultures Lusignan Prairies temporaires/ Poitou- Charentes permanente Auvergne Theix-Laqueuille Prairie permanente

5 F-Lusignan : prairie temporaires/ permanente mean T 11.5 C, P 830mm F-Lus CO2 depuis 2006 CO2 flux tower N2O Paturage (PT) 1.7 UGB ha.yr kg N ha.yr -1 N2O CO2-flux tower N2O Fauche (PP) 4 à 5 yr kg N ha.yr -1

6 depuis Mai 2002 Paturage Mai-Octobre F-Laqueuille prairies permanentes Alt. 1050m, mean T 8 C, 1000mm DOC/DON Flux Tower CO 2 + CH 4 F-Laq Intensive 2.82 ha 1 UGB ha.yr kg N ha.yr-1 (3 splits) DOC/DON Meteo station N 2 O Flux Tower CO 2 + CH 4 Extensive 3.4ha 0.5 UGB ha.yr-1

7 Definition of Carbon sink activity Net Carbon Storage in grasslands F-Laq X X [CO 2 ] = C Vertical wind = w CO 2 flux = w c EC-flux towers (spatial ~ 1 to 3ha ) Net Ecosystem Exchange (NEE) X Equation du bilan carbone de l écosystème Stockage net C (NCS) = NEE + F fumier F récolte - F CH4-C - F produits animaux - F lessivage (i.e. Allard et al. 2007, Soussana et al 2010):

8 Cumulated CO 2 flux : intensive vs. extensive grazing F-Laq NEE (g C m -2 ) Extensive Intensive C sink INTENSIF EXTENSIF EXT NaN INT NEE shows a high inter-annual variability mainly due to climatic conditions. Treatment effect on annual NEE Int>Ext: 2003, 2005, 2008, 2011 Ext>Int: 2004, 2006, 2007, 2010 Cumulated NEE (9 yrs) was 12.5 (Extensive) and 14 (Intensive) t C ha -1 (Klumpp et al 2011)

9 Net carbon sequestration F-Laq Net C Storage (g C m-2 yr-1) NCS = NEE + F CH4-C + F manure + F harvest + F animal-products + F leach Extensiv Intensiv mean EXT 191 g C /m2.yr INT 200 g C /m2.yr Dry Dry Dry Dry Dry NCS confirms high inter-annual variability C sequestration is higher under intensive grazing and fertilisation in dry climatic years (e.g. 2003, 2005, 2011, ) climate seems to exeed over management

10 Cumulated CO 2 flux : grazing vs mowing F-Lus tillage Grazed Cut C sink Cut plots Grazed plots Cut Graz High inter annual variability in NEE NEE is consistently higher under cutting than grazing Management exceeds over climate

11 Net carbon sequestration F-Lus NCS= NEE + F CH4-C + F manure + F harvest + F animal-products + F leach Net C Storage (g C m-2 yr-1) permanent, cut temporary, grazed C sequestration is higher under grazing than under cutting Averaged over 2006 to 2011, the difference in NCS between managements is substantial (254 vs 37 gc m -2 yr -1 for grazing and mowing)

12 Prélèvements de sol Printemps 2012 Permanente grazed/fertilised grassland Intensive (PP) 2.0 Mg C /ha.yr Extensive (PP) 1.9 Mg C /ha.yr Temporary/permanent grassland of contrasted practices Grazed (PT) 2.5 Mg C /ha.yr Mown (PP) 0.37 Mg C /ha.yr EU data (173 sites-yrs) 0.7± 0.13 Mg C /ha.yr Grazed 1.1± 0.2 Mg C /ha.yr Mown 0.7± 0.2 Mg C /ha.yr Can we trust these EC results?

13 Prélèvements de sol Printemps 2012 Soil Sampling Soil inventory was carried out Laq 2004, 2008, 2012 with 50 soil cores /ha (0-60cm depth) Lus 2005, 2009, 2012 with 10 soil cores /ha (0-30cm depth) Lp S SFe Cv Tongues C = 5,7 ± 2,1 mg g -1 ** Matrix C = 2,7 ± 0,7 mg g -1

14 (mg g -1 ) Prélèvements de sol Printemps 2012 Grassland in crop rotation F-Lus Prairie (GG) 1 year 6 months 3 months Prairie culture (GA) Culture (AA) C content after conversion 2 years GG GA AA C stock 0-30cm ( Mg - C/ha; 0-30cm) Pâturage (PT) Fauche (PP) Année? Conversion grassland to crop decreases markedly C content after ploughing

15 Permanente grassland F-Laq Extensive grazing 10cm 20cm 40cm 60cm Intensive grazing C accumulates over time in the 20-60cm soil layer 10cm 20cm 40cm 60cm

16 Permanente grassland Stock changes over time (0-60cm depth, n=50 ) F-Laq C accumulates over time in the 20-60cm soil layer EXT INT Extensif EXT Intensif INT

17 Soil inventory - C flux Method comparision (Mg C ha -1 yr -1 ) (0-30 cm) Mowing (PP) F-Lusignan (0-60 cm) F-Laqueuille Flux Soil Flux Sol Extensive (PP) Grazing (PT) Intensive (PP) Comparing soil inventory data with Net C storage shows a good agreement between methods

18 Les prairies sont des puits de carbone Le stockage de carbone varie fortement entre années, il est pénalisé en année sèche (effets et arrière-effets sécheresse) Le retournement de prairie conduit à une perte importante et rapide de MOS Le niveau de chargement et intensification ne semble pas modifier fortement la vitesse de stockage du carbone Le mode d exploitation fauche / pâture affecte fortement le stockage de carbone (plus élevée au pâturage)

19 Thank you! Merci!