Coupled Carbon and Nitrogen Cycles:

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

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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.
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Prognostic Equations for Canopy Leaf Area (Lc)
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Effect of including SLA gradient, using
prescribed LAI.
Effect of switching from prescribed LAI to fully
prognostic plant/soil model.
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Prescribed LAI, from control simulation with
CLM2.1
Prognostic LAI, from CLM3.CN (N saturation on).
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• 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

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Carbon-only dynamics

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

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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.

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

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• 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