Table 2.
Symbols, definition and estimated or literature value of the sucrose loading model parameters
| Parameter (unit) | Definition | Value |
|---|---|---|
| α (mol CO2 mol−1 PAR) | Leaf photochemical efficiency | 0·0645 |
| β (mmol CO2 m−2 h−1 p.p.m.−1) | CO2 use efficiency | 0·252 |
| kL (dimensionless) | Light extinction coefficient | 0·58 |
| LAI1 (m2 m−2) | Leaf area index above level 1 | 1·6667 |
| LAI2 (m2 m−2) | Leaf area index above level 2 | 1·1 |
| LAI3 (m2 m−2) | Leaf area index above level 3 | 0·3333 |
| K0·5 (mmol sucrose eq. m−2 h−1) | Total leaf carbon concentration at which RL = RL,max/2 | 11·68 |
| k1 (h−1) | First-order rate constant for phloem loading | 3·31 × 10−8 |
| k2 (h−1) | Kinetic parameter for inter-conversion of sucrose and storage carbohydrates | 1·2895 |
| k3 (h−1) | Kinetic parameter for hydrolysis | 0·1555 |
| Su0 (mmol sucrose eq. m−2) | Target sucrose concentration | 0·388 |
| Vmax,L (mmol sucrose eq. m−2 h−1) | Michaelis–Menten constant for phloem loading | 2·95 |
| KM,L (mmol sucrose eq. m−2) | Michaelis–Menten constant for phloem loading | 11·2 |
| Vmax,St (mmol sucrose eq. m−2 h−1) | Michaelis–Menten constant for starch synthesis | 3·16 × 10−2 |
| KM,St (mmol sucrose eq. m−2) | Michaelis–Menten constant for starch synthesis | 37·5 |
Parameter values for α, β and kL were adopted from Bertin and Heuvelink (1993), K0·5 from Gary (1988b), KM,L from Sovonick et al. (1974) and values for LAI were assessed by definition. Other parameters were estimated via automatic calibration using measurements of sucrose, starch and hexose concentrations.