Adopted after the dissertation of Stephen Sitch

where

• C3 pathway:
• C4 pathway:

Components are

• α_c3 and α_c4 are intrinsic quantum efficiencies for CO₂ uptake for C3 and C4 plants, respectively (in source:trunk/par/param.par)
• c_mass=12 molar mass of carbon,
• c_q conversion factor for solar radiation at 550 μm from J/m² to E/m²,
• p_i is the internal partial pressure of CO₂ given as P_i = λ · p_a, p_a is ambient partial pressure,
• λ describes the ratio of the intercellular to ambient CO₂ concentration
• T_stress is the PFT-specific temperature inhibition function, limiting photosynthesis at low and high temperatures,
• Γ_* is the carbon dioxide compensation point.
• The factor λ/λ_mc4 reproduces the effect of reduced p_i on C4 photosynthesis, λ_mc4 is the non-water-stressed value of λ in C4 plants.

Temperature stress T_stress is formulated with PFT-specific parameters T₁ to T₄: $ and calculated in source:trunk/src/lpj/temp_stress.c. This PFT-sepcific temperature inhibition of photosynthesis is not part of the original description by Haxeltine and Prentice 1996, but was introduced by Sitch et al. 2003

Carbon compensation point is determined with the partial pressure of oxygen pO₂ and τ: Γ = (pO₂)/(τ)

τ in the code is calculated in [photosynthesis.c[(https://github.com/PIK-LPJmL/LPJmL/blob/master/src/lpj/photosynthesis.c) as

and reflects the ability of Rubisco to discriminate between CO₂ and O₂.