Increases in the Diffusion Resistances of Leaves in a Carbon Dioxide-Enriched Atmosphere

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Abstract
The stomatal closing reaction to CO2, which has been observed in laboratory studies by many workers, was investigated in plant-growth cabinets under conditions similar to those in glass-houses with CO2-enriched atmospheres. Lettuce and Xanthium plants grown in a normal atmosphere showed the expected stomatal closure in response to increasing CO2 concentrations, and lettuce plants grown in 1000 ppm CO2 showed the same response, even after 4 weeks. Thus there was no evidence of acclimatization of the stomata and it is concluded that they must remain partially closed during CO2-enrichment. Estimates of diffusion resistances to CO2 intake in lettuce leaves showed that in light of 14.4 J m−2 S−1, 880 ppm CO2 in the atmosphere resulted in a concentration of 367 ppm near the mesophyll cell walls. If the stomata remained open this same internal concentration could be achieved with an external concentration of only 640 ppm. There could, therefore, be some economic advantage if stomatal closure were prevented during CO2-enrichment.

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