A Three-dimensional Stomatal CO2Exchange Model Including Gaseous Phase and Leaf Mesophyll Separated by Irregular Interface

A three-dimensional model was constructed for studying the diffusion of CO2molecules from air into stomatal air spaces and further into leaf mesophyll cells. The model covers two different phases, mesophyll and air, with appropriate boundary conditions. Sinks for CO2molecules were obtained from a well-known biochemical photosynthesis model parametrized for Scots pine. The effects of the varying stomatal geometry on the CO2flux and intercellular-air-space (IAS) and mesophyll concentrations were examined. The net CO2flux is sensitive to the size of the IAS–mesophyll interface when the mesophyll transport coefficient is low, equalling the diffusivity of CO2in water. The simulations have revealed an optimum between the volume of the assimilating mesophyll and the air–mesophyll interface. The solubility of CO2molecules into water in the cell surfaces, which depends on temperature and pH, had a clear effect on the flux. Increasing pH from the value indicated by the physical solubility (pH∽6) leads to an increase in the temperature maximum for CO2flux into higher temperatures and to unrealistically high CO2concentrates in the mesophyll.