A 3-D microscale model for Co2 GasTransport in tomato leaves during photosynthesis

Exchange of CO2 in tomato (Solanum lycopersicum L.) leaves was modelled using combined gas diffusion and photosynthesis kinetics in a real 3-D geometric representation of the cellular microstructure, obtained by synchrotron radiation X-ray microtomography. The microscale model for gas exchange accounted for diffusive mass transport of CO2 in the intercellular space (pores), the cell wall network and the intracellular liquid of cells. The photosynthesis kinetics described by the extended Farquhar, von Caemmerer & Berry model were coupled to the gas exchange inside the mesophyll cells. The coupled model was validated by means of gas exchange and chlorophyll fluorescence measurements. The model provides detailed insight into the mechanisms of gas exchange and insight into the effects of changes in ambient CO2 concentration or photon flux density on stomatal and mesophyll conductance. The resistance to diffusion of CO2 from the intercellular air spaces within the leaf through the mesophyll to the sites of carboxylation during photosynthesis depended on the 3-D microstructure of leaf tissue. The model represents an important step forward to study CO2 diffusion coupled to photosynthesis at the leaf tissue level, taking into account its actual 3-D microstructure.