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Shifting allocation & nutrient pools affect C stocks

Shifting allocation & nutrient pools affect C stocks

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Shifting allocation & nutrient pools affect C stocks

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  1. Shifting allocation & nutrient pools affect C stocks

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

  3. The challenge Climate Phenology Albedo, ET CO2 effluxes Vegetation succession Microbial processes priming Soils

  4. Senescence & disturbance Photosynthesis & plant respiration Phenology & allocation Microbial & soil processes Af Lf Cfoliage Rh Ra Ar Lr GPP Croot Clitter D Climate drivers Aw Lw Cwood CSOM/CWD Non linear functions of temperature Feedback from Cf Simple linear functions

  5. Two eddy flux sites Abisko tundra Abisko birch woodland

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

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

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

  9. Emergent ecosystem properties

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

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

  12. Carbon storage (kg m-2) in the soil organic horizon in forest and tundra sites Note: CPMAS 13C NMR analysis suggests tundra SOM also more labile Sjögersten S & Wookey PA (2009) Ambio38, 2-10

  13. 0.5 km Carbon content (%) 0 10 20 30 40 50 60 70 80 Data from Wayolle, Wookey, Williams

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

  15. Soil respiration and litter decomposition: Dovrefjell, Abisko and Joatka summarized Sjögersten S & Wookey PA (2009) Ambio38, 2-10

  16. 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 Project NERC Radiocarbon Facility (Environment), East Kilbride

  17. Heath 1020 y BP 184 y BP

  18. Implications • 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

  19. Older CO2 more 14C enriched

  20. Respiration rates and 14CO2 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

  21. Respiration rates • Respiration peaked mid-season • Plant contribution highest early and mid-season

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

  23. 14 C 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)

  24. Similar results becoming available from Kevo in Finnish Lapland

  25. But CO2 is not the only GHG of interest! Environmental controls on CH4 fluxes are complicated!!

  26. 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

  27. 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