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PhotosynthesisLimitationsThe net CO2 assimilation of a leaf (or net photosynthesis) is given by
In ECOPHYS, the photosynthetic rate is limited by the following two factors, Rubisco and Light 1) RUBISCO - The most common equation for describing the rate of carboxylation of ribulose bisphosphate (RuP2) in the presence of competitive inhibition of oxygen, and saturating RuP2 was proposed by proposed by Farquhar, von Caemmerer and Berry (Farquhar 1980). 2) Light - Wj is the rate of carboxylation limited by the rate of RuBP regeneration in the Calvin cycle. In the following equation, J is the rate of electron transport related to PPFD. where
Vcmax and Jmax are key parameters of the model and they vary by species. These parameters, as well as Km and gamma star vary with temperature (Medlyn, 2002).
From the above curve we can see that when PPFD = 1000, Ci must be greater then approximately 500 in order to be light limited for this particular curve.
Stomatal ConductanceECOPHYS is currently using the Ball-Berry stomatal conductance model, gs = g0 + g1*A*RH/Ci. In the near future, it will have a Leuning/Lohammer Model in place as follows. gs = g0 + a1*A/((Ci - G*)*(1+Ds/Do)) Ozone model -
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where 
,
and 
is the irradiance absorbed by photosystem II. Sp is spectral imbalance and r is leaf reflectance. PPFD (Photosynthetic Photon Flux Density) is the amount of light that reaches a leaf. 