Models of photosynthesis need to and can be upgraded to include the effects of drought, phenological changes, sink activity and carbohydrate accumulation on the light exposure/photosynthetic capacity relationship

Biochemical models of leaf photosynthesis, based on the seminal work of Farquhar et al. (1980), have been widely used to compare photosynthetic performance among plant species and to analyse photosynthetic acclimation to high CO2 concentrations or growth irradiance. Such functional models may also be coupled to radiation transfer models, which are structural models, to simulate photosynthesis at the canopy level. FSPM based on coupled models of leaf photosynthesis and radiation transfer are also used in global change modelling. Such coupled models are based on two key relationships, the first between the amount of leaf nitrogen per unit leaf area (Na) and light exposure or leaf age, and the second between leaf photosynthetic capacity (essentially the light saturated rate of electron transport, Jmax, and the maximal rate of carboxylation, Vcmax) and Na. These fundamental relationhips are implicitly assumed to be constants. Moreover it is generally assumed that Vcmax/Jmax is stable.