1. E COLOGIE ET E COPHYSIOLOGIE F ORESTIERES UMR 1137 INRA UHP

2. CONTEXT GP } NEE => NEP => source or sink ? R ECO } R old R new => IRGA CH 4 => GS => MS

3. OBJECTIVE To understand shifts in processes occuring in the carbon balance of peatlands for restoring their sink activity. 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 CO 2 efflux. To highlight the contribution of ‘new peat’ (acrotelm) respiration versus ‘old peat’ (catotelm) mineralisation to total CO 2 efflux. To quantify the contribution of both sources using stable isotope signature ( 13 C-CO 2 ). To quantify the contribution of both sources using stable isotope signature ( 13 C-CO 2 ). To study climatic influences on these two sources and their partitioning To study climatic influences on these two sources and their partitioning To determine the effects of key plant species on these two sources

4. oFo, ooFo, o nFn, nnFn, n Mass balance equations Mass balance equations Linear mixing model Linear mixing model CALCULATIONS  F,  F = F n + F o [1] F.  = F n.  n + F o.  o [2] o( - o)o( - o)  n  o (  n -  o ) F n /F = [3] Determination of  by Keeling plot Determination of  n and  o by incubating peat cores and collecting evolved CO 2

5. measurements  13 C of living plant material, dead plant material, organic matter in soil cores at different depth;  13 C of CO 2 evolved by these materials in lab incubation (incubation conditions to be defined)  In situ peat respiration (gas exchange chambers and IRGA)  13 C of in situ respired CO 2 (Keeling plot methodology)

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

7. 1. KEELING PLOTS 1/[CO2] -26 -24 -22 -20 -18 -16 -14 -12 -10 00,00050,00100,00150,0020  ‰)  1/[CO2]  = 6196,836*1/[CO2] -24,84 R 2 = 0,969 Soil respiration, Hesse forest Determination of  Determination of  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 13 C depleted litter. In prep.

8. QUESTIONS AND LIMITATION Do the isotopic signatures of ‘old’ and ‘new’ peats be contrasted enough ? Do the isotopic signatures of ‘old’ and ‘new’ peats be contrasted enough ? => long term change in atmospheric 13 C 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’ CO 2 in ‘new’ peat => CH 4 oxidation

9. 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. what we expect

10. 0.5 m 1 m Depleted litter Control litter 1 2 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 13 C depleted litter. In prep.

11.  Maximum contribution : 10% of F CONTRIBUTION OF LITTER DECOMPOSITION  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 13 C depleted litter. In prep.

12. FRACTION LOSS AS CO 2  Litter mass loss 61.5% of initial DM  Annual soil CO 2 efflux 838 gC.m -2  Litter contribution (5%) 42 gC.m -2  Litter mass loss 99 gC.m -2  Fraction loss as CO 2 42 % 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 13 C depleted litter. In prep.