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Coupled Carbon and Nitrogen Cycles:

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... from control simulation with CLM2.1 ... N saturation Introduce fire Carbon-only dynamics Relative temperature ... for temperate deciduous forest. – PowerPoint PPT presentation

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Title: Coupled Carbon and Nitrogen Cycles:


1
Coupled Carbon and Nitrogen Cycles New Land
Biogeochemistry Component for CCSM-3 Peter
Thornton, NCAR
2
CLM3.CN Summary Model Structure and Fluxes
Leaf
Live Stem
Live Coarse Root
Current Storage
Plant Pools
Fine Root
Dead Stem
Dead Coarse Root
Previous Storage
Wood Litter (CWD)
Litter Pools
Litter 1 (Labile)
Litter 2 (Cellulose)
Litter 3 (Lignin)
SOM 1 (fast)
SOM 2 (medium)
SOM 3 (slow)
Soil Organic Matter Pools
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, CN
    stoichiometry)
  • CN stoichiometry f(leaffine root, leafwood)
  • leafwood 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
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5
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.
6
Prognostic Equations for Canopy Leaf Area (Lc)
7
Effect of including SLA gradient, using
prescribed LAI.
Effect of switching from prescribed LAI to fully
prognostic plant/soil model.
8
Prescribed LAI, from control simulation with
CLM2.1
Prognostic LAI, from CLM3.CN (N saturation on).
9
  • Offline tests completed
  • Canopy Interception off155 PgC/yr, on120
    PgC/yr
  • Resolution T42120 PgC/yr, T31118 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

10
Carbon-only dynamics
  • Relative temperature sensitivities typically
    result in enhanced C source under warming.
  • No direct feedback from decomposition to
    vegetation growth.

11
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.

12
NEE response to 1 C step change (temperate
deciduous broadleaf forest)
sink
Coupled C-N model
C-only model
source
13
  • Next steps CAM stand-alone testing
  • T31 same configuration as IPCC pre-industrial
    control (need for new diagnostics)
  • N saturation on, short spinup (lt 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.

14
  • Medium-range plans
  • Fully coupled simulations (with Moore ocean
    ecosystem model).
  • Introduce disturbance history information for
    historical simulations
  • Asynchronous N deposition coupling (J.-F.
    Lamarques talk tomorrow).
  • Longer-range plans
  • Fully coupled chemistry simulations
  • Other limiting nutrients (phosphorous)
  • Dissolved species and river transport
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