Shifting allocation & nutrient pools affect C stocksShifting allocation & nutrient pools affect C stocks

Arctic Biosphere-Atmosphere Coupling across multiple Scales ABACUS

Plant &Soil processes Chamber Fluxes

Eddy fluxesAirborne fluxesAnd remote sensing

Earthobservation

Isotopelabelling

The challengeThe challenge

Vegetation

Soils

Climate

priming

succession

Albedo, ETPhenology

CO2 effluxes

Microbialprocesses

GPP Croot

Cwood

Cfoliage

Clitter

CSOM/CWD

Ra

Af

Ar

Aw

Lf

Lr

Lw

Rh

D

Photosynthesis &plant respiration

Phenology &allocation

Senescence & disturbance

Microbial &soil processes

Climate drivers

Non linear functionsof temperatureSimple linear functionsFeedback from Cf

Two eddy flux sitesTwo eddy flux sites

Abisko birch woodland

Abisko tundra

Carbon exchange in tundra heathCarbon exchange in tundra heath

Observed (EC) Modelled (SPA)mol m-2 s-1

Time of day Time of day

GPP = 594 gC m-2

Time of day

Tim

e o

f ye

ar

Net ecosystem exchange (measured) [ mol m-2 s-1]

0 400 800 1200 1600 2000

2007.3

2007.4

2007.5

2007.6

2007.7

2007.8

2007.9

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

Time of day

Tim

e o

f ye

ar

Net ecosystem exchange (modelled) mol m-2 s-1

400 800 1200 1600 2000 2400

2007.3

2007.4

2007.5

2007.6

2007.7

2007.8

2007.9

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

Data from Evans and Harding

Carbon exchange in birch woodlandCarbon exchange in birch woodland

Time of day

Tim

e o

f ye

ar

Net ecosystem exchange (measured) mol m-2 s-1

0 400 800 1200 1600 2000

2007.3

2007.4

2007.5

2007.6

2007.7

2007.8

2007.9

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

Time of day

Tim

e o

f ye

ar

Net ecosystem exchange (modelled) mol m-2 s-1

400 800 1200 1600 2000 2400

2007.3

2007.4

2007.5

2007.6

2007.7

2007.8

2007.9

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

Observed (EC) Modelled (SPA)mol m-2 s-1

Time of day Time of day

GPP = 1080 gC m-2

Data from Evans and Harding

Leaf growthand senescence

Fine rootdynamics

Data from Poyatos and Sloan

0

200

400

600

800

1000

1200

1400

150 170 190 210 230 250 270 290

Time (DOY 2007)

Mea

n l

eaf

area

(m

m2 )

50

60

70

80

90

100

110

Sm

iula

ted

lea

f m

ass

(g m

-2)

Constraining models with biometric dataConstraining models with biometric data

Emergent ecosystem propertiesEmergent ecosystem properties

Tundra heath

Mountain birch

Problems modelling soil organic matter dynamics!Problems modelling soil organic matter dynamics!

Sofie Sjögersten (‘DART’ Project)Universities of Uppsala & Nottingham

Iain Hartley (‘ABACUS’ Project)University of Stirling

Audrey Wayolle, SAGES

Dovrefjell Abisko Joatka

Mountain birch forest 6.3 1.3 2.0

Tundra heath 10.1 3.9 2.4

Carbon storage (kg mCarbon storage (kg m-2-2) in the soil ) in the soil organic horizon in forest and tundra organic horizon in forest and tundra sitessites

Note: CPMAS 13C NMR analysis suggests tundra SOM also more labile

Sjögersten S & Wookey PA (2009) Ambio 38, 2-10

0.5 km

Data from Wayolle, Wookey, Williams

0 10 20 30 40 50 60 70 80

Carbon content (%)

Physico-chemicalEnvironment (P)

Decomposerorganisms (O)

Litterquality (Q)

After Swift, Heal & Anderson (1979)

+ Rhizodeposition

Soil respiration and litter decomposition: Dovrefjell, Soil respiration and litter decomposition: Dovrefjell, Abisko and Joatka summarizedAbisko and Joatka summarized

Sjögersten S & Wookey PA (2009) Ambio 38, 2-10

• Use of ‘bomb’ 14C peak (late 1950s to early 60s) in soils to investigate soil organic matter turnover (Iain Hartley with Mark Garnett, NERC RCF)

• IPY ABACUS ProjectNERC Radiocarbon Facility (Environment), East Kilbride

80

100

120

140

160

180

200

1900 1920 1940 1960 1980 2000 2020

Year AD

Rad

ioca

rbo

n c

on

ten

t (%

mo

der

n)

Data sources:

Reimer, P. J., et al. 2004 IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP. Radiocarbon 46, 1029-1058.

Q Hua and M Barbetti, "Review of Tropospheric Bomb 14C Data for Carbon Cycle Modeling and Age Calibration Purposes", (2004) Radiocarbon 46: 1273-1298.

Depth (cm)

0 1 2 3 4 5 6 7

14C

(%

mo

der

n)

90

95

100

105

110

115

120

125

130

Current atmosphere

Pre-bomb

1020 y BP

184 y BP

Site Depth 14C (% Modern)

Birch Forest 0-1 cm 135.321-2 cm 111.87Mineral 88.09

Heath

ImplicationsImplications

• Calculations:– Pool size and MRT– Contribution of different layers to CO2 flux

• Much bomb C, little old C• Contribution of pre-bomb carbon to CO2 flux

should be very small• Not surprising in freely-drained soils

80

100

120

140

160

180

200

1900 1920 1940 1960 1980 2000 2020

Year AD

Rad

ioca

rbo

n c

on

ten

t (%

mo

der

n)

Data sources:

Reimer, P. J., et al. 2004 IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP. Radiocarbon 46, 1029-1058.

Q Hua and M Barbetti, "Review of Tropospheric Bomb 14C Data for Carbon Cycle Modeling and Age Calibration Purposes", (2004) Radiocarbon 46: 1273-1298.

Older CO2 more14C enriched

Respiration rates and Respiration rates and 1414COCO22 sampling sampling

• Two plot types:– Clipped and trenched = soil respiration only– Control = vegetation and soil respiration

• Measured respiration rates• Collected CO2 for 14C analysis

– Late May / early June– Mid July– Early September

Respiration ratesRespiration rates

• Respiration peaked mid-season

• Plant contribution highest early and mid-season

Date

1/6/07 1/7/07 1/8/07 1/9/07

Res

pira

tion

rate

(g

CO

2 m

-2 h

-1)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2 controlCT

0.0

0.2

0.4

0.6

0.8

1.0

Date

1/6/07 1/7/07 1/8/07 1/9/07 P

ropo

rtio

nal c

ontr

ibut

ion

0.0

0.2

0.4

0.6

0.8

1.0

VegSoil

Tundra heath Tundra heath

Birch forest Birch forest

• Early indications that mountain birch might be involved in ‘priming’ the decomposition of older SOM: labile litter or rhizodeposition?

14C

(%

Mo

der

n)

100

102

104

106

108

110

112 SoilUnderstorey

May July September100

102

104

106

108

110

112 SoilEco

(a) BIRCH

(b) HEATH

14 14 C work - conclusions and implicationsC work - conclusions and implications

• Carbon turning over is mainly 5-10 years old• Mid-season positive “priming” of 14C-enriched

soil organic matter in birch forest• Partially explains the thin organic horizon in

birch forest• Implications for change in tree-line

(importance of plant species distributions)

• Similar results becoming available from Kevo in Finnish Lapland

But COBut CO2 2 is not the only GHG of interest!is not the only GHG of interest!

Environmental controlson CH4 fluxes arecomplicated!!

Environmental controlson CH4 fluxes arecomplicated!!

ConclusionsConclusions• Productivity, biomass and soil C stocks are highly

variable over a range of spatial scales• Some basic ecosystem emergent properties are

strongly related to GPP• We still struggle to understand and model below-

ground processes• Vegetation change will engender significant

changes in SOM• We can’t assume that increased NPP will also be

associated with increased C sequestration in soils

Acknowledgements:R. Baxter, M. Disney, J. Evans, B. Fletcher, M. Garnett,J. Gornall, R. Harding, I. Hartley, D. Hopkins, B. Huntley, T. Hill, P. Ineson, J. Moncrieff, G. Phoenix, V. Sloan, R. Poyatos, A. Prieto-Blanco, M. Sommerkorn, J. Subke, P. Stoy, L. Street, T. Wade, A. Wayolle, M. Williams,C. Wilson, and all the ABACUS team