The effect of internal conductance on photosynthesis

Internal conductance describes the movement of CO₂ from the sub-stomatal cavities to site of carboxylation. This involves the diffusion of CO₂ across cell walls, plasma membrane, cytosol and chloroplast envelope before finally recahing the sites of carboxylation. Many studies over the past two decades have shown that internal conductance (g_i) is finite and imposes a limitation on photosynthesis only slightly smaller than that due to stomatal conductance (g_s). Nevertheless, we still know little about what determines internal conductance, how it varies among species, or how it affects instantaneous water-use efficiency and rates of photosynthesis per unit nitrogen (PNUE).

A series of experiments are examining: 1) variation in internal conductance among species; 2) if internal conductance is related to nutrient supply; and 3) if there are consistent or predictable relationships among internal conductance, stomatal conductance and photosynthesis. we are also examining the effect of internal conductance on leaf-level economics (i.e. rates of photosynthesis per unit water lost or leaf N).

Funding: ARC Discovery grant

Partner investigators: Gilbert Ethier (University of Victoria), Nigel Livingston (University of Victoria), Erwin Dreyer (INRA), Mark Adams (UNSW)

Location: Field and glasshouse experiments in Australia, France & Canada

Figure: Internal conductance may affect water-use efficiency by up to 25%. Data are modeled for Eucalyptus globulus seedlings.

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