23A 



1 CHARLES S. YENTSCH 



2 as fast as they can and further increases in light will 



3 not be accompanied by further increases in photosynthesis 



4 because the whole rate is light saturated, that is that 



5 the enzymes just will not work the reaction any faster. 



g I am assuming that the biologists concerned 



7 with the measurements in this report have utilized this 



g value as what 1 term the maximum or the light saturated 



9 rate of photosynthesis, and indeed I think they were very 



IQ wise in doing this because this is a very sensitive indi- 



H cator, a very good means of getting the pulse rate of a 



12 group of phytoplankton in any water mass. 



13 



15 



The trouble with it, however, is that it is 



14 sensitive to practically every factor that one can think 



of that controls the growth rate of plants. And I don't 



16 wish to color this discussion with a great deal of technical 



17 jargon, but if one, for example, changes the water tem- 



18 perature, say, from 20 degrees to 10 degrees Centigrade, 



19 this reduces the carbon fixation rate of most phytoplankton 



20 by as much as about 25 percent. If you change it from 20 



21 to 5 degrees, you can reduce the rate of carbon fixation 



22 about 75 percent. So my noain point here is that very, 



23 very small changes, relatively small changes, in the 



24 environment can make very, very great changes in the 

 maximum rate of photosynthesis. 



25 



