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E COLOGIE ET E COPHYSIOLOGIE F ORESTIERES UMR 1137 INRA UHP

E COLOGIE ET E COPHYSIOLOGIE F ORESTIERES UMR 1137 INRA UHP. NEE => NEP => source or sink ?. CH 4. }. => GS. R ECO. }. GP. => IRGA. => MS. R new. R old. CONTEXT. OBJECTIVE.

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E COLOGIE ET E COPHYSIOLOGIE F ORESTIERES UMR 1137 INRA UHP

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  1. ECOLOGIE ET ECOPHYSIOLOGIE FORESTIERES UMR 1137 INRA UHP

  2. NEE => NEP => source or sink ? CH4 } => GS RECO } GP => IRGA => MS Rnew Rold CONTEXT

  3. OBJECTIVE • To understand shifts in processes occuring in the carbon balance of peatlands for restoring their sink activity. • To highlight the contribution of ‘new peat’ (acrotelm) respiration versus ‘old peat’ (catotelm) mineralisation to total CO2 efflux. • To quantify the contribution of both sources using stable isotope signature (13C-CO2). • To study climatic influences on these two sources and their partitioning • To determine the effects of key plant species on these two sources

  4. F,d Fn,dn Fo,do [1] F = Fn + Fo (d-do) Determination ofdby Keeling plot Determination ofdnanddo by incubating peat cores and collecting evolved CO2 [3] Fn/F = [2] F.d= Fn.dn+ Fo.do (dn- do) CALCULATIONS • Linear mixing model • Mass balance equations

  5. measurements => d 13C of living plant material, dead plant material, organic matter in soil cores at different depth; => d 13C of CO2 evolved by these materials in lab incubation (incubation conditions to be defined) => In situ peat respiration (gas exchange chambers and IRGA) => d 13C of in situ respired CO2 (Keeling plot methodology)

  6. LICOR Li-6200 By-pass Teflon filter Dessicant (MgClO) Sampling system (Plexiglas) Butyl septum Exetainer Tube (10 ml) MATERIAL

  7. Soil respiration, Hesse forest -10 -12 -14 -16 d (‰) -18 -20 -22 d = 6196,836*1/[CO2] -24,84 R2 = 0,969 -24 -26 0 0,0005 0,0010 0,0015 0,0020 1/[CO2] 1. KEELING PLOTS • Determination ofd Ngao J., Epron D., Brechet C. and Granier A. Estimating the contribution of leaf litter decomposition to soil carbon efflux in a beech forest using 13C depleted litter. In prep.

  8. QUESTIONS AND LIMITATION • Do the isotopic signatures of ‘old’ and ‘new’ peats be contrasted enough ? => long term change in atmospheric 13C abundance (-6.5‰ to -8.0‰ over the last 50 years) => progressive enrichment of SOM by microbial discrimination or preferential decomposition => photosynthetic refixation of ‘old’ CO2 in ‘new’ peat => CH4 oxidation

  9. what we expect Novák M., Buzek F., Adamová M. 1999. Vertical trends in 13C, 15N and 34S ratios in bulk Sphagnum peat. Soil Biology and Biochemistry 31: 1343-1346.

  10. 1 1 m Depleted litter 2 Control litter 0.5 m EXPERIMENTAL DESIGN Ngao J., Epron D., Brechet C. and Granier A. Estimating the contribution of leaf litter decomposition to soil carbon efflux in a beech forest using 13C depleted litter. In prep.

  11. CONTRIBUTION OF LITTER DECOMPOSITION • Maximum contribution : 10% of F • Mean annual contribution : 5% Ngao J., Epron D., Brechet C. and Granier A. Estimating the contribution of leaf litter decomposition to soil carbon efflux in a beech forest using 13C depleted litter. In prep.

  12. Fraction loss as CO2 42 % FRACTION LOSS AS CO2 • Annual soil CO2 efflux 838 gC.m-2 • Litter mass loss 61.5% of initial DM • Litter mass loss 99 gC.m-2 • Litter contribution (5%) 42 gC.m-2 Ngao J., Epron D., Brechet C. and Granier A. Estimating the contribution of leaf litter decomposition to soil carbon efflux in a beech forest using 13C depleted litter. In prep.

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