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

Peter Thornton, NCAR

CLM3.CN: Summary Model Structure and Fluxes

Leaf

FineRoot

DeadStem

DeadCoarse Root

LiveStem

LiveCoarse Root

PreviousStorage

CurrentStorage

Wood Litter(CWD)

Litter 1(Labile)

Litter 2(Cellulose)

Litter 3(Lignin)

SOM 1(fast)

SOM 2(medium)

SOM 3(slow)

PlantPools

LitterPools

Soil OrganicMatter Pools

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

allom

allomdemand C

NGPPN

deadwood

243

livewood

243

fineroot

1

leafallom CN

)f1)(f1(f

CN

)f1(ff

CN

f

CN

1N

))f1(ff1)(g1(C 2311allom

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.

allomnewleaf C

GPPC

)f1(ffCC

fffCC

)f1(fCC

ffCC

fCC

432newleafotnewdeadcro

432newleafotnewlivecro

43newleafmnewdeadste

43newleafmnewliveste

1newleaftnewfineroo

Overlying Leaf Area (L)(top=0)

SL

A

(bottom=Lc)

LmSLASLA 0L

dLSLA

1C

cL

0 Lleaf

m

SLA))SLAlog(mCexp(L 00leaf

c

Prognostic Equations for Canopy Leaf Area (Lc)

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

AtmosphericCO2

VegetationBiomass

SoilOrganicMatter

Carbon-only dynamics

• Relative temperature sensitivities typically result in enhanced C source under warming.

• No direct feedback from decomposition to vegetation growth.

C flux

Legend

Tempsensitivity

C flux

Legend

Tempsensitivity

N flux

AtmosphericCO2

VegetationBiomass

SoilOrganicMatter

AtmosphericN species

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

(temperate deciduous broadleaf forest)

C-only model

Coupled C-N modelsink

sour

ce

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