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!

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

13. DovrefjellAbiskoJoatka Mountain birch forest 6.31.32.0 Tundra heath10.13.92.4 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 0 10 20 30 40 50 60 70 80 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

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