Table 1.
Symbols and units used
| Variable | Definition | Unit |
|---|---|---|
| A | Net assimilation rate | µmol m–2 s–1 |
| C c | CO2 concentration in chloroplasts | µmol mol–1 |
| C i | CO2 concentration in intercellular airspace | µmol mol–1 |
| C i–C c | CO2 drawdown from intercellular airspace to chloroplasts | µmol mol–1 |
| D a | Diffusion coefficient for CO2 in the gas phase | m2 s–1 |
| d leaf | Leaf density | g cm–3 |
| D w | Aqueous phase diffusion coefficient for CO2 | m2 s–1 |
| f ias | Fraction of mesophyll occupied by intercellular airspace | Dimensionless |
| f pal | Fraction of mesophyll cell volume comprised of palisade tissue | Dimensionless |
| H/(RT k) | Henry′s law constant | Dimensionless |
| ∆L ias | Effective diffusion path length in the gas-phase | m |
| L mes | Total length of chloroplasts facing the intercellular airspace | m |
| L mes | Total length of mesophyll cells facing the intercellular airspace | m |
| p i | Effective porosity in the given part of the diffusion pathway | Dimensionless |
| Q | Incident quantum flux density | µmol m–2 s–1 |
| R | Gas constant | Pa m3 K–1 mol–1 |
|
Mesophyll resistance of exposed chloroplast surface area per unit of leaf area | m2chlor s mol–1 |
| r cellular | Cellular resistance, sum of r cw, r pl, r cyt, r env, and r str | s m–1 |
| R d | Dark respiration rate | µmol m–2 s–1 |
| r cw | Cell wall resistance | s m–1 |
| r pl | Plasma membrane resistance | s m–1 |
| r cyt | Cytoplasm resistance | s m–1 |
| r env | Chloroplast envelope resistance | s m–1 |
| r str | Stroma resistance | s m–1 |
| r gas | Gas phase resistance | s m–1 |
| r liq | Liquid phase resistance | s m–1 |
| r m | Mesophyll diffusion resistance | m2 s mol–1 |
| S c/S | Chloroplast surface area exposed to intercellular airspace | |
| per unit of leaf area | m2 m–2 | |
| s mes | Cross-sectional surface area of mesophyll cells in micrograph | m2 |
| s pal | Cross-sectional area of palisade mesophyll cells in micrograph | m2 |
| s s | Cross-sectional area of mesophyll cells in micrograph | m2 |
| S c,pal/S | S c/S for palisade mesophyll | % |
| S c,spon/S | S c/S for spongy mesophyll | % |
| S c/S mes | Ratio of exposed chloroplast to mesophyll surface areas | Dimensionless |
| S mes/S | Surface area of mesophyll cells exposed to airspace per unit of leaf area | m2 m–2 |
| t chlor | Chloroplast thickness | µm |
| t cw | Cell wall thickness | µm |
| T k | Absolute temperature | K |
| t leaf | Leaf thickness | mm |
| t mes | Mesophyll thickness | mm |
| W | Width of the section measured | m |
| γ | Curvature correction factor | Dimensionless |
| γf,i | Proportional reduction of diffusion conductance in the cytosol and in the stroma compared with free diffusion in water | Dimensionless |
|
Diffusion path tortuosity | m m–1 |
|
Hypothetical CO2 compensation point without R d | µmol mol–1 |
| ΦPSII | Effective quantum yield of PSII | Dimensionless |
| ξ | Leaf absorptance | Dimensionless |
| ε | Fraction of electrons absorbed by PSII | Dimensionless |