Abstract
The present paper briefly presents certain facts which extend present knowledge regarding the effects of some of the following external conditions on the velocity of respiration and photosynthesis in the marine kelp Nereocystis. Some of the facts do apply, and the others may apply to respiration and photosynthesis of plants in general.
Uniform strips 1 × 10 cm. were cut from the frond of the kelp. The oxygen exchange in respiration and photosynthesis was determined by Winkler's method. Specially made bottles of 25 cc. volume were used. One strip was placed in each bottle for a determination. Three duplicate bottles with strips were used for the same concentration of oxygen, cyanide, etc. Each figure in the tables is, therefore, the average of three duplicate, simultaneous determinations. During the tests the experimental bottles were suitably immersed in the open sea, which afforded a constant temperature to within ±0.5° C. during any one experiment. Light intensity was the same in all the tests of any one experiment, but varied more or less from one experiment to another. Suitable control experiments showed that the effects reported are not due to differences in hydrogen ion concentration.
Effect of oxygen concentration on the rate of respiration and photosynthesis. It is a familiar fact that increase in concentration of oxygen increases the rate of oxygen consumption in many kinds of plants. It is not such a generally recognized fact that increase in concentration of oxygen decreases the rate of photosynthesis. These two effects of oxygen concentration on Nereocystis are shown by the three experiments performed simultaneously, and given in Table I.
Column 1 shows the initial concentration of dissolved oxygen in sea water at which the rates of respiration and photosynthesis were tested.
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