Diffusion of inorganic carbon across an unstirred layer: a simplified quantitative approach

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Abstract
The quantitative approach used here is based on a model comprising a well‐stirred medium, an unstirred layer, and a CO2 absorbing leaf. The unstirred layer is divided up by planes into a number of sub‐layers. Within each plane the concentration of each solute is everywhere the same as is the electric potential. These variables constitute the basic data. Thus the planes were characterized by their pH value.An equation is derived which enables the calculation of the basic data of a plane from the known data of another plane. In this way it is possible to calculate the basic data for all planes. From these data the rate of assimilation, the thickness of the unstirred layer and its sub‐layers, the fluxes across the sub‐layers and the conversions among the carbon components can be estimated.The CO2 flux decreases, and the HCO−3 flux increases towards the leaf. There are negative fluxes of OH& and CO2–3. H+ fluxes are of minor importance and can be ignored if the pH of the medium is higher than 8.0, provided no non‐inorganic C buffers with appropriate pKa are present.The significance of the carbon diffusion facilitating effect of an inorganic carbon system is expressed in various ways. The values obtained represent maxima, as the assumption is made that the equilibrium reactions are very fast.It is argued that even better effects are possible if the back‐diffusion of CO2–3 could be prevented by lowering the pH of the unstirred layer.