The widely used, mechanistically based Farquhar model
(Farquhar et al. 1980; von Caemmerer & Farquhar 1981)
of C3 carbon assimilation, modified according
Harley & Tenhunen (1991), was employed. Essential to this
model is that CO2 uptake is eiter entirely
limited bei RUBISCO activity and the respective partial
pressure of the competing gasses CO2 and
O2 at the sites of carboxylation or by electron
transport, which limits the rate at which RuBP is regerated.
Limitations of RuBP regeneration arising from the
avaiability of inorganic phosphate for photophosphorylation
(WP; Sharkey 1985 are not considered in this model
But this model considers nitrogen dependencies of
Vcmax, Pml and Rdark.
Leaf internal CO2 partial pressure is calculated
from the net photosynthesis and stomatal conductance
according Fick's law. Due to the fact that net
photosynthesis and stomatal conductance are not independent, the model must solve for internal
CO2 partial pressure in an iterative fashion (Harley &
Tenhunen 1991; Harley & Baldocchi 1995).