|MadSci Network: Botany|
Growing plants at above normal atmospheric pressure would involve a hyperbaric chamber. One recent study on ginkgo found as much as a 250% increase in the photosynthesis rate when the carbon dioxide was increased 500% and atmospheric pressure was increased 25%. I contacted the lead author, Sara Decherd, and she kindly told me that they found no significant effect on photosynthesis with a 25% increase in atmospheric pressure alone. She was also not aware of much other research on plant growth in hyperbaric chambers. It seems to be an area that has not been thoroughly studied. The ginkgo research was recently featured in a news release, "A Lot of Hot Air: How the Dinosaurs Grew So Monstrous." NASA has done work on growing plants at less than atmospheric pressure in hypobaric chambers. Hypobaric greenhouses with one-sixteenth the pressure of an Earth atmosphere may be required for Mars colonization. At normal atmospheric pressures, increasing the carbon dioxide concentration up to about 1,000 ppm often increases plant growth. Current atmospheric carbon dioxide is about 360 ppm. Thus, you might expect a positive effect on plant growth in a hyperbaric chamber. I doubt a soda bottle would be a satisfactory hypobaric chamber. It would be difficult and expensive for a school student to maintain an elevated carbon dioxide level in a hyperbaric plant growth chamber because a plant can rapidly deplete the carbon dioxide given its low concentration and the limited chamber volume. Be very cautious if you try to make your own hyperbaric chamber because an explosion is always a possibility. It would be much easier to demonstrate effects of carbon dioxide enrichment at normal atmospheric pressures. A soda bottle system to inexpensively induce carbon dioxide deficiency in plants can be built using rubber stoppers, aquarium tubing, aquarium valves and an aquarium air pump (Hershey 1992, 1995). The same system could be used to elevate the carbon dioxide level using dry ice or acid mixing with calcium carbonate as a source of carbon dioxide. References PHOTOSYNTHETIC RATE RESPONSES OF GINKGO BILOBA (VAR.: MAGYAR) TREES TO COMBINED ATMOSPHERIC ENRICHMENT OF CO2, O2 AND INCREASED ATMOSPHERIC PRESSURE A Lot of Hot Air: How the Dinosaurs Grew So Monstrous NASA Greening Mars Hershey, D.R. 1995. Plant Biology Science Projects. New York: Wiley. Hershey, D.R. 1992. Plants Can't Do Without CO2. Science Teacher. 59(3): 41-43 Mar. Effect of Carbon Dioxide Enrichment and Light Crop ecology: Carbon dioxide
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