Abstract
Substantial lateral CO(2) 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 CO(2) 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 CO(2) flux. Lateral diffusion rates were low when PPFD <300 micromol m(-2) s(-1) but approached saturation in moderate PPFD (300 micromol m(-2) s(-1)) when lateral CO(2) diffusion represented 15% to 24% of the normal CO(2) assimilation rate. Smaller patches and higher ambient CO(2) concentration increased lateral CO(2) diffusion rates. Calculations with a two-dimensional diffusion model supported these observations that lateral CO(2) diffusion over short distances inside dicotyledonous leaves can be important to photosynthesis. The results emphasize that supply of CO(2) 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.
Highlights
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)
Part of the disagreement in these recent articles may reside in the different techniques used and the different species examined and part in the importance of lateral CO2 transfer varying with net CO2 assimilation rate (A; Lawson and Morison, 2006)
The chlorophyll a fluorescence images show a substantial reduction of Fq#/Fm# under the patch in the wildtype plants at an 300 mmol mol21, ambient CO2 mole fraction (Ca) of and at the patch center, Fq#/Fm#
Summary
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). Pieruschka et al (2006) used chlorophyll a fluorescence images to examine light-shade boundaries in leaves of two homobaric species, faba bean (Vicia faba) and tobacco (Nicotiana tabacum), and two heterobaric species, dwarf bean and soybean (Glycine max) While they found that there was no detectable lateral diffusion in the heterobaric species, there could be sufficient lateral CO2 diffusion in the homobaric species when stomatal conductance was low to increase photosynthesis over distances of up to 3 mm. They suggested that lateral CO2 transfer from darkened to illuminated sections of leaves in patchy sunlight might be important in permitting some CO2 assimilation when stomata are closed (Pieruschka et al, 2006). We conclude that lateral CO2 diffusion over short distances up to approximately 1 mm can contribute substantially to leaf CO2 assimilation rate in a number of dicotyledonous species, including some classified as heterobaric
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
