Photosynthetic Uptake of Free CO₂, by the Roots of <i>Lobelia dortmanna</i>

Abstract

Abstract Lobelia dortmanna L. is probably unable to utilize HCO 3 − and uses only free CO 2 for photosynthesis as shown by the Winkler method. A 14 C technique was used to show that if CO 2 is added to the water around roots, photosynthesis increases 3–5 times more than when the corresponding amount of CO 2 is added to the water surroundings the leaves. As the CO 2 content in lakes where Lobelia grows is very limited, Lobelia must absorb CO 2 from the sediment, and the carbon dioxide will have to diffuse from the roots up into the leaves through the intercellular system of the plant. In conjunction with Lobelia's CO 2 uptake from the sediment O 2 is liberated. The plant, therefore, acts as an oxygen pump, which oxidizes the sediment down to a depth of 20 cm.