Measurement of the Carbon Dioxide Compensation Point and the Rate of Loss of14CO2in the Light and Dark in Some Bryophytes

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Abstract
The CO2 compensation point at 25 °C and 250 μEinsteins m−2 s−1 wasmeasured for 27 bryo-phyte species, and was found to be in the range of 45–160 μl CO2 I−1 air. Under the same conditions Zea mays gave a value of 11 μl I−1 and Horde um vulgare 76 μI−1. The rate of loss of photosynthetically fixed 14CO2 in the light and dark in six bryophytes (three mosses, two leafy liverworts, one thalloid liverwort) was determined in CO2-free air and 100% O2. The rate of 14CO2 evolution in the light was less than that in the dark in CL2-free air, but in 100% O2 the rate in the light increased, so that in all but the leafy liverworts it was greater than that in the dark. Raising the temperature tended to increase the rate of 14CO2 evolution into CO2-free air both in the light and dark, so that the light/dark (L/D) ratio did not greatly vary. The lower rate of loss of 14CO2 in the light compared tothe dark could be due to partial inhibition of ‘dark respiration’ reactions in the light, a low rate of glycolate synthesis and oxidation, or partial reassimilation of the 14CO2 produced, or a combination of some or all of these factors.

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