Lateral gas diffusion inside leaves
2005
Diffusion of CO₂ inside leaves is generally regarded to be from the substomatal cavities to the assimilating tissues, i.e. in the vertical direction of the leaf blades. However, lateral gas diffusion within intercellular air spaces may be much more effective than hitherto considered. In a previous work it was demonstrated that, when 'clamp-on' leaf chambers are used, leaf internal 'CO₂ leakage' beyond the leaf chamber gaskets may seriously affect gas exchange measurement. This effect has been used in the present paper to quantify gas conductance (g[subscript leaf,l], mmol m⁻² s⁻¹) in the lateral directions within leaves and significant differences between homo- and heterobaric leaves were observed. For the homobaric leaves, lateral gas conductance measured over a distance of 6 or 8 mm (the widths of the chamber gaskets) was 2-20% of vertical conductance taken from published data measured over much smaller distances of 108-280 [micro]m (the thickness of the leaves). The specific internal gas diffusion properties of the leaves have been characterized by gas conductivities ([Formula: see text] [micro]mol m⁻¹ s⁻¹). Gas conductivities in the lateral directions of heterobaric leaves were found to be small but not zero. In homobaric leaves, they were between 67 and 209 [micro]mol m⁻¹ s⁻¹ and thus even larger than those in the vertical direction of the leaf blades (between 15 and 78 [micro]mol m⁻¹ s⁻¹). The potential implications for experimentalists performing gas exchange measurements are discussed.
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