SiriusQuality2 is a process-based model consisting of eight sub-models (modules) that describe on a daily time step crop phenology (Phenology sub-model), canopy development (Leaf Layer Expansion sub-model), accumulation and partitioning of dry mass (DM; Light Interception and Use Efficiency and Dry Mass Allocation sub-models) and N (N Allocation, and Root Growth and N UptakeReferences sub-models), including responses to shortage in the supply of soil water (Soil Drought sub-model) and N (dealt with in the N Allocation sub-model), and accumulation and partitioning of grain DM and N (Grain sub-model). Two additional sub-model describe crop evapotranspiration and soil N and water balances (Addiscott & Whitmore, 1991, Jamieson, Semenov, Brooking & Francis, 1998b).
The Phenology sub-model calculates the durations of six development phases, including pre-emergence (sowing to emergence), leaf production (emergence to flag leaf ligule appearance), flag leaf ligule appearance to anthesis, anthesis to beginning of grain fill, grain filling, and maturation (Jamieson et al., 1998a). The anthesis date is mainly determined by the rate of leaf production (1/phyllochron) and the final leaf number. The final leaf number is calculated by daylength (photoperiod) and temperature (vernalization) response sub-routines (Brooking, Jamieson & Porter, 1995, Jamieson et al., 1998a). Canopy development is simulated in the Leaf Layer Expansion sub-model as a series of leaf layers associated with individual main-stem leaves, and tiller production is simulated through the potential size of each layer (Lawless, Semenov & Jamieson, 2005).
The Light Interception and Use Efficiency sub-model calculates the amount of light intercept by each leaf layer using the turbid medium approach (Monsi & Saeki, 2005) and uses it to produce biomass at an efficiency (light use efficiency) calculated from temperature, air CO2 concentration, soil water deficit, leaf nitrogen content per unit surface area (specific leaf N) and the ratio of diffuse to direct radiation (Jamieson et al., 2000). The total above-ground biomass at any time is the sum of the daily rate of biomass accumulation of each leaf layer, which, in turn, is the product of LUE and intercepted photosynthetically active radiation (PAR) by the leaf layers (Monteith, 1977). The canopy light extinction coefficient (KL) is assumed to be independent of N and water shortages (Robertson & Giunta, 1994). Part of the biomass produced each day is allocated to the stem so that a target constant specific dry mass of the leaf laminae (SLWp) and sheaths (SSWp) is maintained. After the end of the endosperm cell division period, all new biomass plus a constant proportion of the labile leaf and stem biomass at the end of the endosperm cell division phase are allocated to grains.
Crop N uptake is driven by canopy expansion. The vertical distribution of leaf N follows the light distribution (Bertheloot, Martre & Andrieu, 2008b) and the ratio of nitrogen to light extinction coefficients is determined by the crop N status (Lötscher, Stroh & Schnyder, 2003) and the size of the canopy (Moreau et al., 2012). As for the biomass, any N not allocated to the leaves is allocated to the stem if its N concentration is less than its maximum. After anthesis, the capacity of the root system to uptake N from the soil decreases linearly with thermal time (Martre et al., 2006). After the end of the endosperm cell division stage, the rate of N transfer to grains is determined by the stem and leaf N concentrations and follows a first order kinetics (Berthelootet al., 2008a, 2008b).
The following links provided a detailed description of the main sub-models (pdf):
Coordination of leaf expansion
References
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Bertheloot J., Andrieu B., Fournier C. & Martre P. (2008a) A process-based model to simulate nitrogen distribution in wheat (Triticum aestivum) during grain-filling. Functional Plant Biology, 35, 781-796.
Bertheloot J., Martre P. & Andrieu B. (2008b) Dynamics of light and nitrogen distribution during grain filling within wheat canopy. Plant Physiology, 148, 1707-1720.
Brooking I.R., Jamieson P.D. & Porter J.R. (1995) The influence of daylength on final leaf number in spring wheat. Field Crops Research, 41, 155-165.
Jamieson P.D., Berntsen J., Ewert F., Kimball B.A., Olesen J.E., Pinter Jr P.J., Porter J.R. & Semenov M.A. (2000) Modelling CO2 effects on wheat with varying nitrogen supplies. Agriculture, Ecosystems and Environment, 82, 27-37.
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Moreau D., Allard V., Gaju O., Le Gouis J., Foulkes M.J. & Martre P. (2012) Acclimation of leaf nitrogen to vertical light gradient at anthesis in wheat is a whole-plant process that scales with the size of the canopy. Plant Physiology, 160, 1479-1490.
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