An elucidatory model of oxygen's partial pressure inside substomatal cavities
<p>A parsimonious model based on Dalton's law reveals substomatal cavities to be dilute in oxygen (O<span class="inline-formula"><sub>2</sub>)</span>, despite photosynthetic O<span class="inline-formula"><sub>2</sub></span&g...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2025-02-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/22/785/2025/bg-22-785-2025.pdf |
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| Summary: | <p>A parsimonious model based on Dalton's law reveals substomatal cavities to be dilute in oxygen (O<span class="inline-formula"><sub>2</sub>)</span>, despite photosynthetic O<span class="inline-formula"><sub>2</sub></span> production. Transpiration elevates the partial pressure of water vapour but counteractively depresses the partial pressures of dry air's components – proportionally including O<span class="inline-formula"><sub>2</sub></span> – preserving cavity pressurization that is negligible as regards air composition. Suppression of O<span class="inline-formula"><sub>2</sub></span> by humidification overwhelms photosynthetic enrichment, reducing the O<span class="inline-formula"><sub>2</sub></span> molar fraction inside cool or warm leaves by hundreds or thousands of parts per million. This elucidates the mechanisms that realize O<span class="inline-formula"><sub>2</sub></span> transport: diffusion cannot account for up-gradient conveyance of O<span class="inline-formula"><sub>2</sub></span> from dilute cavities through stomata to the more aerobic atmosphere. Rather, leaf O<span class="inline-formula"><sub>2</sub></span> emissions depend on non-diffusive transport via mass flow forced by cavity pressurization, which is not negligible in the context of dynamics. Non-diffusive O<span class="inline-formula"><sub>2</sub></span> expulsion overcomes massive inward O<span class="inline-formula"><sub>2</sub></span> diffusion to force net O<span class="inline-formula"><sub>2</sub></span> emission. At very high leaf temperatures, mass flow also influences transport of water vapour and carbon dioxide, physically decoupling their exchanges and reducing water-use efficiency, independently of stomatal regulation.</p> |
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| ISSN: | 1726-4170 1726-4189 |