CARBON DIOXIDE BALANCE AT HIGH LIGHT INTENSITIES

Abstract

The important feature of the apparatus is the closed system which permits a continuous and vigorous circulation of air about the plant, and an easy control of humidity, temp., and evaporating power of the air. This system kept the roots cool, yet the temp. of the air surrounding the leaves could be varied between 4[degree] and 37[degree] C. One hydrophyte, 7 mesophytes, and 2 xerophytes were used; the land plants were potted. All the plants at some temperature quickly reduced the CO2 in the chamber to 0.01 volume % (over 24 hrs. for some plants). As the 0.01% concentration is approached, the curves break fairly sharply[long dash]a close approximation to Blackman''s ideal graph for limiting factors. The limiting % of CO2 is independent of leaf properties and temp. (providing the high temps. introduce no abnormal metabolism) . This independence of CO2 balance on temp. suggests that a dark reaction of photosynthesis has a temp. coefficient equal to the temp. coefficient of respiration. Plants segregate themselves into definite groups according to their behavior at high temps. This CO2 balance 2 depends on the conc. of dissolved CO2 and not on the total CO2 (carbonic acid plus bicarbonates).