Carbon balance in a heterogeneous cutover bog in the Jura Mountains. Estelle Bortoluzzi, Daniel Epron, Daniel Gilbert, Alexandre Buttler

WP 02: Carbon sequestration by peatland vegetation Objectives 1. Identify and compare the vegetation communities colonizing abandoned cut- over mire sites 2. Determine effects of key plant species used in peat restoration on carbon sequestration 3. Determine net primary production and biomass accumulation 4. Estimate net ecosystem productivity from seasonal determinations of photosynthesis and respiration in a transparent enclosure

WP 02: Carbon sequestration by peatland vegetation Milestones: M3: Site selection for survey and setting up of field experiment M4: Survey of vegetation in cut-over sites and production measurements M5: Rates of photosynthesis and respiration in cut-over sites (year1) and experiment (year 2-3) M6: Biomass accumulation and growth biometry of keystone species in experiment (years 2-3)

WP 02: Carbon sequestration by peatland vegetation Deliverables: D5: Identification of key plant species successfully occupying abandoned sites and their potential for restoring peat accumulation D6: Rates of carbon return from key species used in the restoration of cut-over sites D7: Rates of C fixation on an area basis, evaluation of carbon sequestration through net primary production, estimation of hourly, daily and yearly net ecosystem productivity => Estelle thesis on June 15 th => Manuscript under revision in New Phytologist

WP 02: Carbon sequestration by peatland vegetation CO 2 CH 4 P G - R A CO 2 RERE Carbon sequestration PP N EE N TOC - R H - F CH4

Measurements A two year survey Open through flow transparent chamber (Ciras 1, PPSystems) for CO 2 fluxes Closed darkened chambers for CH 4 accumulation (micro-GC CP 4900, Varian) 11 collars on three vegetation types: bare peat, recent regeneration (Eriophorum) and advanced regeneration (Sphagnum) Environmental variables (air and peat temperature, global radiation and photosynthetic photon flux density, rainfall, water table level …) Biotic variables (Leaf Area Index, bryophyte density, dessication index) => Vegetation Index (VI) (0 to 1):

Ecosystem respiration Bare Peat Recent Advanced Days of years 2004 and 2005 R E (µmolCO 2 m -2 s -1 )

Air temperature, main determinant of R E T A (°C) Bare peat Recent R. Advanced R. R E (µmolCO 2 m -2 s -1 )

Residuals of R E related to water table on bare peat Bare Peat WT (level of water table) (m) Residuals of R E (µmolCO 2 m -2 s -1 )

Residuals of R E related to vegetation index Residuals of R E (µmolCO 2 m -2 s -1 ) Recent Advanced VI (relative unit)

Predicted R E R E predicted (µmolCO 2 m -2 s -1 ) Bare peat Recent Advanced R E measured (µmolCO 2 m -2 s -1 )

Net ecosystem exchange under saturating irradiance Days of years 2004 and 2005 EE Nsat (µmolCO 2 m -2 s -1 ) Recent Advanced

Gross photosynthesis under saturating irradiance P Bsat (µmol CO 2 m -2 s -1 ) Recent Advanced Days of years 2004 and 2005 P Bsat = EE Nsat + R E

Air temperature, main determinant of P Bsat T A (°C) P Bsat (µmol CO 2 m -2 s -1 ) Recent Advanced

Residuals of P Bsat related to vegetation index VI (relative unit) Recent Advanced Residual of P Bsat (µmolCO 2 m -2 s -1 )

Predicted EE Nsat Recent Advanced EE Nsat measured (µmolCO 2 m -2 s -1 ) EE Nsat predicted (µmolCO 2 m -2 s -1 )

Light response curves of EE N PPFD (µmol/m 2 /s) EE N (µmolCO 2 m -2 s -1 ) Advanced collar 5, j596

Predicted EE N EE N predicted (µmolCO 2 m -2 s -1 ) EE N measured (µmolCO 2 m -2 s -1 ) Récent Advanced

CH 4 efflux Days of years 2004 and 2005 Bare peat Recent Advanced F CH4 (nmole m -2 s -1 )

CH 4 efflux related to water table on bare peat F CH4 (nmol m -2 s -1 ) WT (m ) Bare peat

CH 4 efflux related to leaf area index of vasculars F CH4 (nmol m -2 s -1 ) LAI (m 2 m -2 ) Recent Advanced

Simulation: Knowing: 1.Half a hour global radiation and it conversion factor to photon flux density 2.Half a hour air and peat temperature 3.Seasonal variation of water table 4.Seasonal variation of leaf area index, bryophyte density and moss dessication index => Rates of net ecosystem productivity and methane efflux can be estimated at hourly, daily and yearly on an area basis and use to evaluate of carbon sequestration

Daily fluxes F CO2 ( g C m -2 d -1 ) Days of years 2004 and 2005 PBPB RERE Advanced P B and R E Advanced E N Bare peat EE N Recent P B and R E Recent E N

Annual carbon balance (g C m -2 y -1 ) 2004Bare peatRecentAdvanced PBPB ~ ~ 474 RERE ~ ~ -297 F CH ~ ~ -2.3 Bilan-2267 ~ ~ Bare peatRecentAdvanced PBPB 279 ~ ~ 525 RERE -19 ~ ~ ~ -340 F CH ~ ~ ~ -2.7 Bilan-19 ~ ~ ~ 183

Conclusions : 1.Bare peat is a weak carbon source and vegetated areas are strong carbon sinks 2.Net carbon exchange slightly higher for advanced than for recent regeneration 3.High variability among collars within a given stage of regeneration 4.Higher sensitivity to summer drought in Sphagnum covered plots (advanced regeneration) 5.Higher methane efflux in vascular covered plots ( recent regeneration)

Perspective : Site comparison, meta analysis … AuteursCountryTypeMethodC balance (g C m -2 y -1 ) Aurela et al., (2004)FinlandMinerotrophicEddy flux22 Alm et al., (1997)FinlandOmbrotrophicChamber73 Lafleur et al., (2001)CanadaOmbrotrophicEddy flux68 Lafleur et al., (2003)CanadaOmbrotrophicEddy flux71 Lafleur et al., (2003)CanadaOmbrotrophicEddy flux9 Alm et al., (1999)FinlandOmbrotrophic, very dry year Chamber-90 Waddington et al., (2002)QuebecOmbrotrophic, after cutting Chamber-88 ~ -112 This studyLe Russey Bare peat Recent Advanced Chambers -19 ~ ~ ~ 183