ECOLOGIE ET ECOPHYSIOLOGIE FORESTIERES UMR 1137 INRA UHP

ECOLOGIE ET ECOPHYSIOLOGIE FOREST�IERES UMR 1137 INRA UHP

CONTEXT GP } } NEE => NEP => source or sink ? CH 4 RECO Rnew Rold => GS => IRGA => MS

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

F, d ü Linear mixing model CALCULATIONS ü Mass balance equations F n , dn F o , do F = Fn + Fo [1] F. d = Fn. dn + Fo. do [2] Determination of dn and do by incubating peat cores and collecting evolved CO 2 [3] Determination of d by Keeling plot Fn/F = (d - d o ) (d n - d o )

measurements => d 13 C of living plant material, dead plant material, organic matter in soil cores at different depth; => d 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) => d 13 C of in situ respired CO 2 (Keeling plot methodology)

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

ü Determination of d 1. KEELING PLOTS -10 Soil respiration, Hesse forest -12 -14 d (‰) -16 -18 -20 -22 d = 6196, 836*1/[CO 2] -24, 84 -26 R 2 = 0, 969 0 0, 0005 0, 0010 0, 0015 1/[CO 2] 0, 0020 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.

QUESTIONS AND LIMITATION ü 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

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

EXPERIMENTAL DESIGN 1 1 m Depleted litter 2 Control litter 0. 5 m 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.

CONTRIBUTION OF LITTER DECOMPOSITION Ø Maximum contribution : 10% of F Ø 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.

FRACTION LOSS AS CO 2 Ø Annual soil CO 2 efflux 838 g. C. m-2 Ø Litter mass loss 61. 5% of initial DM Ø Litter contribution (5%) 42 g. C. m-2 Ø Litter mass loss 99 g. C. m-2 Ø 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.