Presets
Playback
Environment
Light, CO2, temperature and air dryness.
Leaf
Stomata and biochemical capacity.
Layers
Model checks
The science
The Farquhar-von Caemmerer-Berry model
Net CO2 assimilation of a C3 leaf is the smaller of a Rubisco-limited and an electron-transport (RuBP regeneration) limited gross rate, minus day respiration:
A = min(Wc, Wj) − Rd, Wc = Vcmax (Ci − Γ*) / (Ci + Kc(1 + O/Ko)), Wj = J (Ci − Γ*) / (4 Ci + 8 Γ*)The electron transport rate J follows light through the non-rectangular hyperbola θJ² − (αI + Jmax)J + αI Jmax = 0 (θ = 0.7, α = 0.3). Temperature enters as an Arrhenius factor exp[Ea(T − 25) / (298.15 R T)] with the activation energies of Bernacchi et al. (2001).
Coupling to the stomata
CO2 must diffuse through the stomata: A = (gs/1.6)(Ca − Ci). Where this supply line crosses the demand curve is the operating point; the page finds it by bisection. Transpiration is E = gs D / P with vapour pressure deficit D.
Honest simplifications
- Steady state, one big leaf; no mesophyll conductance, photoinhibition, triose-phosphate limitation or acclimation of Vcmax to temperature.
- gs is a free slider here (a real leaf adjusts it with light, humidity, CO2 and water status).
- Particle animation is symbolic; the number of molecules shown is proportional to the fluxes, not to real counts.
What to try
- Load Shade leaf and raise the light: the dot moves along the RuBP-limited branch until Rubisco takes over.
- Compare Glacial CO2 with Elevated CO2 at the same light: assimilation changes a lot because Ci changes.
- Close the stomata in Drought: the supply line steepens, Ci drops and water-use efficiency rises.
- Sweep the temperature in the third graph to find the optimum near 30 C.