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

Coupled Carbon and Nitrogen Cycles:
New Land Biogeochemistry Component for CCSM-3
Peter Thornton, NCAR
CLM3.CN: Summary Model Structure and Fluxes
Plant
Pools
Current
Storage
Leaf
Live
Stem
Live
Coarse Root
Previous
Storage
Fine
Root
Dead
Stem
Dead
Coarse Root
Wood Litter
(CWD)
Litter
Pools
Soil Organic
Matter Pools
Litter 1
(Labile)
Litter 2
(Cellulose)
Litter 3
(Lignin)
SOM 1
(fast)
SOM 2
(medium)
SOM 3
(slow)
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)
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
Nallom 
1
f1
f  f (1  f 2 ) f3 (1  f 4 )(1  f 2 )

 3 4

CN leaf CN fineroot
CN livewood
CN deadwood
Callom  (1  g1 )(1  f1  f3 (1  f 2 ))
Ndemand  GPP 
Nallom
Callom
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.
C newfineroot  C newleaf  f1
C newlivestem  C newleaf  f 3  f 4
C newleaf 
GPP
Callom
C newdeadstem  C newleaf  f 3  (1  f 4 )
C newlivecroot  C newleaf  f 2  f 3  f 4
C newdeadcroot  C newleaf  f 2  f 3  (1  f 4 )
SLA
Prognostic Equations for Canopy Leaf Area (Lc)
SLAL  SLA0  m  L
(bottom=Lc)
(top=0)
Overlying Leaf Area (L)
Cleaf 
Lc
1
0 SLA L dL
Lc 
exp( Cleaf  m  log(SLA 0 ))  SLA 0
m
Effect of including SLA gradient, using
prescribed LAI.
Effect of switching from prescribed
LAI to fully prognostic plant/soil
model.
Prescribed LAI, from control
simulation with CLM2.1
Prognostic LAI, from
CLM3.CN (N saturation on).
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
Atmospheric
CO2
Legend
Vegetation
Biomass
C flux
Temp
sensitivity
Soil
Organic
Matter
Carbon-only dynamics
• Relative temperature sensitivities typically result in enhanced
C source under warming.
• No direct feedback from decomposition to vegetation growth.
Atmospheric
CO2
Atmospheric
N species
Legend
Vegetation
Biomass
C flux
N flux
Temp
sensitivity
Soil
Organic
Matter
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.
NEE response to +1° C step change
sink
(temperate deciduous broadleaf forest)
Coupled C-N model
C-only model
Next steps: CAM stand-alone testing
T31: same configuration as IPCC pre-industrial control
(need for new diagnostics)
1. N saturation on, short spinup (< 100 yrs) to get coupled
climate.
2. CAM climate into offline run with N saturation turned
off: long spinup (actually an accelerated spin-down)
3. CAM-CLM run from 1, with N saturation off, to observe
short-term differences in CLM response in spin-down
phase (compared to 2).
4. Re-couple from results of 2, run to steady state.
5. Multiple branches from endpoint of 4: CO2 expts, Ndep
expts, landuse expts (C4MIP + Ndep).
6. CCSM coupling from 4.
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