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BIOENERGETICS AND PHOTOSYNTHESIS

Lateral CO₂ Diffusion inside Dicotyledonous Leaves Can Be Substantial: Quantification in Different Light Intensities^1,[W],[OA]

Department of Biological Sciences, University of Essex, Colchester, United Kingdom (J.I.L.M., T.L.); and Laboratoire d'Ecologie Systématique et Evolution, Département d'écophysiologie végétale, Faculté des sciences d'Orsay, Université Paris XI, 91405 Orsay, France (G.C.)

Substantial lateral CO₂ diffusion rates into leaf areas where stomata were blocked by grease patches were quantified by gas exchange and chlorophyll a fluorescence imaging in different species across the full range of photosynthetic photon flux densities (PPFD). The lateral CO₂ flux rate over short distances was substantial and very similar in five dicotyledonous species with different vascular anatomies (two species with bundle sheath extensions, sunflower [Helianthus annuus] and dwarf bean [Phaseolus vulgaris]; and three species without bundle sheath extensions, faba bean [Vicia faba], petunia [Petunia hybrida], and tobacco [Nicotiana tabacum]). Only in the monocot maize (Zea mays) was there little or no evident lateral CO₂ flux. Lateral diffusion rates were low when PPFD <300 µmol m^–2 s^–1 but approached saturation in moderate PPFD (300 µmol m^–2 s^–1) when lateral CO₂ diffusion represented 15% to 24% of the normal CO₂ assimilation rate. Smaller patches and higher ambient CO₂ concentration increased lateral CO₂ diffusion rates. Calculations with a two-dimensional diffusion model supported these observations that lateral CO₂ diffusion over short distances inside dicotyledonous leaves can be important to photosynthesis. The results emphasize that supply of CO₂ from nearby stomata usually dominates assimilation, but that lateral supply over distances up to approximately 1 mm can be important if stomata are blocked, particularly when assimilation rate is low.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: James I.L. Morison (morisj{at}essex.ac.uk).

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.107318

^* Corresponding author; e-mail morisj{at}essex.ac.uk.

Received August 15, 2007; accepted September 10, 2007; published September 28, 2007.