ECOLOGIE ET

ECOPHYSIOLOGIE

FORESTIERESUMR 1137 INRA UHP

CONTEXTCONTEXT

GP

}

NEE => NEP => source or sink ?

RECO}RoldRnew

=> IRGA

CH4

=> GS

=> MS

OBJECTIVEOBJECTIVE

To understand shifts in processes occuring in the To understand shifts in processes occuring in the carbon balance of peatlands for restoring their sink carbon balance of peatlands for restoring their sink activity.activity.

To highlight the contribution of ‘new peat’ (acrotelm) To highlight the contribution of ‘new peat’ (acrotelm) respiration versus ‘old peat’ (catotelm) mineralisation to respiration versus ‘old peat’ (catotelm) mineralisation to total COtotal CO22 efflux. efflux.

To quantify the contribution of both sources using To quantify the contribution of both sources using stable isotope signature (stable isotope signature (1313C-COC-CO22).).

To study climatic influences on these two sources and To study climatic influences on these two sources and their partitioningtheir partitioning

To determine the effects of key plant species on these two sources

Fo, ooFn, nn

Mass balance equationsMass balance equations

Linear mixing model Linear mixing model

CALCULATIONSCALCULATIONSF,

F = FF = Fnn + F + F

oo [1]

F.F. = F= Fnn..nn + F+ F

oo..oo

[2]

( - oo)

(nn - oo)Fn/F = [3] Determination ofDetermination of by Keeling plotby Keeling plot

Determination ofDetermination of nn andand o o by by

incubating peat cores and incubating peat cores and collecting evolved COcollecting evolved CO22

measurementsmeasurements

1313C of living plant material, dead plant material, organic C of living plant material, dead plant material, organic matter in soil cores at different depth;matter in soil cores at different depth;

1313C of COC of CO22 evolved by these materials in lab incubation evolved by these materials in lab incubation

(incubation conditions to be defined)(incubation conditions to be defined)

In situIn situ peat respiration (gas exchange chambers and IRGA) peat respiration (gas exchange chambers and IRGA)

1313C C of in situof in situ respired CO respired CO22 (Keeling plot methodology) (Keeling plot methodology)

LICOR Li-6200LICOR Li-6200

Sampling system

(Plexiglas)

Teflon filter

Dessicant (MgClO)

Butyl septum

Exetainer Tube (10 ml)

By-pass

MATERIALMATERIAL

1. KEELING PLOTS1. KEELING PLOTS

1/[CO2]

-26

-24

-22

-20

-18

-16

-14

-12

-10

0 0,0005 0,0010 0,0015 0,0020

‰

)

= 6196,836*1/[CO2]1/[CO2] -24,84

R2 = 0,969

Soil respiration, Hesse Soil respiration, Hesse forestforest

Determination ofDetermination 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 13C depleted litter. In prep.

QUESTIONS AND LIMITATIONQUESTIONS AND LIMITATION

Do the isotopic signatures of ‘old’ and ‘new’ peats be Do the isotopic signatures of ‘old’ and ‘new’ peats be contrasted enough ?contrasted enough ?

=> long term change in atmospheric => long term change in atmospheric 1313C abundance C abundance

(-6.5‰ to -8.0‰ over the last 50 years)(-6.5‰ to -8.0‰ over the last 50 years)

=> progressive enrichment of SOM by microbial => progressive enrichment of SOM by microbial discrimination or preferential decompositiondiscrimination or preferential decomposition

=> photosynthetic refixation of ‘old’ CO=> photosynthetic refixation of ‘old’ CO22 in ‘new’ in ‘new’

peatpeat

=> CH=> CH44 oxidation oxidation

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 expectwhat we expect

0.5 m0.5 m

1 m1 mDepleted litterDepleted litter

Control litterControl litter

1

2

EXPERIMENTAL DESIGNEXPERIMENTAL 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.

Maximum contribution : 10% of FMaximum contribution : 10% of F

CONTRIBUTION OF LITTER DECOMPOSITIONCONTRIBUTION OF LITTER DECOMPOSITION

0

2

4

6

8

10

12

0 30 60 90 120 150 180 210 240 270 300 330 360

Julian days

FL/F (%)

Mean annual contribution : 5%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.

FRACTION LOSS AS COFRACTION LOSS AS CO22

Litter mass loss Litter mass loss 61.5% of initial DM61.5% of initial DM

Annual soil COAnnual soil CO22 efflux efflux

838 gC.m838 gC.m-2-2

Litter contribution (5%) Litter contribution (5%) 42 gC.m42 gC.m-2-2

Litter mass loss Litter mass loss 99 gC.m99 gC.m-2-2

Fraction loss as COFraction loss as CO22

42 %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 13C depleted litter. In prep.