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Coupled Carbon and Nitrogen Cycles: New Land Biogeochemistry Component for CCSM-3

Coupled Carbon and Nitrogen Cycles: New Land Biogeochemistry Component for CCSM-3 Peter Thornton, NCAR. CLM3.CN: Summary Model Structure and Fluxes. Current Storage. Leaf. Live Stem. Live Coarse Root. Plant Pools. Previous Storage. Fine Root. Dead Stem. Dead Coarse Root.

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Coupled Carbon and Nitrogen Cycles: New Land Biogeochemistry Component for CCSM-3

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  1. Coupled Carbon and Nitrogen Cycles: New Land Biogeochemistry Component for CCSM-3 Peter Thornton, NCAR

  2. CLM3.CN: Summary Model Structure and Fluxes Current Storage Leaf Live Stem Live Coarse Root Plant Pools Previous Storage Fine Root Dead Stem Dead Coarse Root Wood Litter (CWD) Litter Pools Litter 1 (Labile) Litter 2 (Cellulose) Litter 3 (Lignin) Soil Organic Matter Pools SOM 1 (fast) SOM 2 (medium) SOM 3 (slow)

  3. CLM3.CN: Summary of Principle Algorithms • Sun/shade canopy = f(leaf properties, LAI, solar zenith angle) • SLA = f(LAI) • Photosynthesis = f(Vcmax, …) • Vcmax = f(SLA, Leaf N, fNRub, Rubisco activity, T) • Allocation = f(available C, available N, C:N stoichiometry) • C:N stoichiometry = f(leaf:fine root, leaf:wood) • leaf:wood = f(annual NPP) • Leaf Area Index (LAI) = f(SLA, Leaf C) • Phenology: evergreen, seasonal deciduous, stress deciduous • Plant respiration = f(plant N, T, NPP) • Heterotrophic respiration = f(Tsoil, soil water, available C, substrate quality, available N)

  4. Prognostic Equations for C and N Allocation f1 = new fine root : new leaf f2 = new coarse root : new stem f3 = new stem : new leaf ( = 0.1 + 0.0025 ANPP) f4 = new live wood : new total wood g1 = growth respiration per unit new growth Total N demand (plant plus microbial immobilization) reconciled with mineral N availability, with competition between plants and microbes on the basis of relative demand. Modify GPP (downregulation) to reflect N limitation, if any.

  5. SLA (bottom=Lc) (top=0) Overlying Leaf Area (L) Prognostic Equations for Canopy Leaf Area (Lc)

  6. Effect of including SLA gradient, using prescribed LAI. Effect of switching from prescribed LAI to fully prognostic plant/soil model.

  7. Prescribed LAI, from control simulation with CLM2.1 Prognostic LAI, from CLM3.CN (N saturation on).

  8. Offline tests completed: • Canopy Interception: off=155 PgC/yr, on=120 PgC/yr • Resolution: T42=120 PgC/yr, T31=118 PgC/yr • Tests underway (not yet analyzed): • Dynamic wood allocation • Gap-phase mortality turned on • Final offline tests: • Corrected canopy interception • Turn off N saturation • Introduce fire

  9. Carbon-only dynamics • Relative temperature sensitivities typically result in enhanced C source under warming. • No direct feedback from decomposition to vegetation growth.

  10. Coupled Carbon-Nitrogen dynamics • Strong feedback between decomposition and plant growth: soil mineral N is the primary source of N for plant growth. • Can result in a shift from C source to C sink under warming.

  11. NEE response to +1° C step change (temperate deciduous broadleaf forest) sink Coupled C-N model C-only model source

  12. Next steps: CAM stand-alone testing • T31: same configuration as IPCC pre-industrial control (need for new diagnostics) • N saturation on, short spinup (< 100 yrs) to get coupled climate. • CAM climate into offline run with N saturation turned off: long spinup (actually an accelerated spin-down) • CAM-CLM run from 1, with N saturation off, to observe short-term differences in CLM response in spin-down phase (compared to 2). • Re-couple from results of 2, run to steady state. • Multiple branches from endpoint of 4: CO2 expts, Ndep expts, landuse expts (C4MIP + Ndep). • CCSM coupling from 4.

  13. Medium-range plans • Fully coupled simulations (with Moore ocean ecosystem model). • Introduce disturbance history information for historical simulations • Asynchronous N deposition coupling (J.-F. Lamarque’s talk tomorrow). • Longer-range plans • Fully coupled chemistry simulations • Other limiting nutrients (phosphorous) • Dissolved species and river transport

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