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Shifting allocation & nutrient pools affect C stocks.

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Presentation on theme: "Shifting allocation & nutrient pools affect C stocks."— Presentation transcript:

1 Shifting allocation & nutrient pools affect C stocks

2 Arctic Biosphere-Atmosphere Coupling across multiple Scales ABACUS Plant & Soil processes Chamber Fluxes Eddy fluxesAirborne fluxes And remote sensing Earth observation Isotope labelling

3 The challenge Vegetation Soils Climate priming succession Albedo, ET Phenology CO 2 effluxes Microbial processes

4 GPPC root C wood C foliage C litter C SOM/CWD RaRa AfAf ArAr AwAw LfLf LrLr LwLw RhRh D Photosynthesis & plant respiration Phenology & allocation Senescence & disturbance Microbial & soil processes Climate drivers Non linear functions of temperature Simple linear functions Feedback from C f

5 Two eddy flux sites Abisko birch woodland Abisko tundra

6 Carbon exchange in tundra heath Observed (EC) Modelled (SPA)  mol m -2 s -1 Time of day GPP = 594 gC m -2 Data from Evans and Harding

7 Carbon exchange in birch woodland Observed (EC) Modelled (SPA)  mol m -2 s -1 Time of day GPP = 1080 gC m -2 Data from Evans and Harding

8 Leaf growth and senescence Fine root dynamics Data from Poyatos and Sloan Constraining models with biometric data

9 Emergent ecosystem properties

10 Tundra heath Mountain birch Problems modelling soil organic matter dynamics!

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12 Sofie Sjögersten (‘DART’ Project) Universities of Uppsala & Nottingham Iain Hartley (‘ABACUS’ Project) University of Stirling Audrey Wayolle, SAGES

13 DovrefjellAbiskoJoatka Mountain birch forest Tundra heath Carbon storage (kg m -2 ) in the soil organic horizon in forest and tundra sites Note: CPMAS 13 C NMR analysis suggests tundra SOM also more labile Sjögersten S & Wookey PA (2009) Ambio 38, 2-10

14 0.5 km Data from Wayolle, Wookey, Williams Carbon content (%)

15 Physico-chemical Environment (P) Decomposer organisms (O) Litter quality (Q) After Swift, Heal & Anderson (1979) + Rhizodeposition

16 Soil respiration and litter decomposition: Dovrefjell, Abisko and Joatka summarized Sjögersten S & Wookey PA (2009) Ambio 38, 2-10

17 Use of ‘bomb’ 14 C peak (late 1950s to early 60s) in soils to investigate soil organic matter turnover (Iain Hartley with Mark Garnett, NERC RCF) IPY ABACUS Project NERC Radiocarbon Facility (Environment), East Kilbride

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19 1020 y BP 184 y BP Heath

20 Implications Calculations: – Pool size and MRT – Contribution of different layers to CO 2 flux Much bomb C, little old C Contribution of pre-bomb carbon to CO 2 flux should be very small Not surprising in freely-drained soils

21 Older CO 2 more 14 C enriched

22 Respiration rates and 14 CO 2 sampling Two plot types: – Clipped and trenched = soil respiration only – Control = vegetation and soil respiration Measured respiration rates Collected CO 2 for 14 C analysis – Late May / early June – Mid July – Early September

23 Respiration rates Respiration peaked mid-season Plant contribution highest early and mid-season

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

25 14 C work - conclusions and implications Carbon turning over is mainly 5-10 years old Mid-season positive “priming” of 14 C-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)

26 Similar results becoming available from Kevo in Finnish Lapland

27 But CO 2 is not the only GHG of interest! Environmental controls on CH 4 fluxes are complicated!!

28 Conclusions 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

29 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


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