Carbon Cycle

A simulation model, Carbon cYCle in Land Ecosystems (Sim-CYCLE), which is a process-based terrestrial model (overview in Table 1; for more details, see Ito and Oikawa, 2002), is globally applied to the simulation of vegetation productivity. In the model, the ecosystem structure is simplified into a six-compartment system (atmosphere, foliage, stem, root, litter, and humus), while 16 carbon flows represent ecosystem dynamics (growth, mortality, and reproduction) (Fig. 1).

Net primary production (NPP, gCm-2day-1 or y-1) is defined as the amount of plant dry-matter production during a given period, and is

Table 1: Brief description of the processes in Sim-CYCLE (see Ito and Oikawa (2002) for details)

Process

Synopsis

Environmental dependence Key parameters l o

O"

PAR/PPFD Net radiation Evapotranspiration

Photosynthesis Respiration

Allocation

Litterfall Decomposition

Iqbals's empirical model: diffused radiation and direct radiation are separated Albedo model for short-wave radiation, and empirical model for long-wave radiation. Penman-Monteith model is used for potential evapotranspiration, limited by available water (soil moisture and precipitation) Empirical single-leaf gas exchange is scaled up to canopy scale, based on the Monsi-Saeki theory Two-component model (growth and maintenance) with exponential temperature response for maintenance respiration

Theoretically optimal LAI determines allocation to leaf. Allometric shoot-root proportion is considered Constant senescence rate and seasonal deciduousness Two-layer model (dependent on soil moisture and temperature)

Latitude, season, cloudiness

VPD, surface temperature, cloudiness

Albedo, snow cover

Temperature, wind, soil water, Canopy conductance precipitation, VPD

Temperature, soil water, PPFD, day-length, atmospheric CO2

Temperature

Indirectly on photosynthesis and leaf phenology

Temperature, precipitation

(leaf phenology)

Soil moisture, soil temperature

Quantum yield, light-saturated photosynthetic rate, LAI, light attenuation coefficient Specific respiration rate, temperature coefficient (Q10)

Optimum LAI, root/shoot ratio

Specific mortality

Specific decomposition rate

CO CO CD

Climate map (UEA/CRU)

Climate map (NCEP/NCAR-reanalysis)

Wind velocity Specific humid. Surface temp. Soil temp.

Climate map (UEA/CRU)

Air temp. Precip. Cloudiness Vapor press.

CARBON CYCLE MODEL

CO2 in free atmosphere net ecosystem production

CO2 in canopy boundary layer

APAR map

Biome map (Olson et al., 1983)

Biome map (Olson et al., 1983)

Natural Cropland

INPUT

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