Factors affecting productivity in fertilized salt water 459 



the standard error of estimate. The relation of photosynthesis to Hght in natural 

 aquatic populations has been reviewed in some detail by Edmondson (in press). 



Because of considerations just discussed, and because certain mflucniial factors 

 were not measured, calculations were made to ascertain how much of the variation 

 might have been ehminated by more rigorous control of conditions. Data published 

 by Fleischer (1935) permit evaluation of variation when measurements of photo- 

 synthesis of pure cultures of Chlorella sp. were taken as a function of chlorophyll 

 concentration under uniform environmental conditions. The amount of chlorophyll 

 in the population was varied by raising the cells in media deficient in one of the 

 nutrients; thus, in the example selected, the past history of the various cultures 

 differed only in the concentration of iron in the medium in which the colls had grown. 

 Otherwise, conditions were uniform, the cells of fairly uniform age being suspended 

 in a standard medium for the measurement of photosynthesis under constant illumina- 

 tion and temperature. Despite the carefully controlled environment, and the presence 

 of only one species, there was variation in the amount of photosynthesis accom- 

 plished by a given amount of chlorophyll. Some of Fleischer's series were somewhat 

 less variable. Measurements made from Fleischer's Fig. 7 shows that the cocflicient 

 of correlation is 0-97. His data are plotted in the insert of Fig. 4, with which they may 

 be directly compared. It has been shown that differences in the age of cultures of 

 Chlorella make a difference in the effectiveness of chlorophyll, as do differences in 

 the culture conditions. (Emerson, Green and Webb, 1940; Winoklr, 1949; Sar- 

 gent, 1940). Thus, with material and conditions very much more uniform than in 

 the tanks, there was a variabiUty which was a relatively large part of that found in 

 the tanks. 



EFFECT OF TAXONOMIC COMPOSITION OF POPULATION 



The analysis made above takes no account of the qualitative changes in the taxono- 

 mic composition of the populations. It might be expected that, as the specific composi- 

 tion of the plankton changed, there would be consequent changes in the photo- 

 synthetic rate for given amounts of chlorophyll and light. If so, there are two possi- 



biUties to discuss. 



If the appearance or disappearance of particular forms were to make a large 

 difference in the relationships under discussion, it might be argued that the largest 

 differences would be made by changes in the representation of major taxonomic 

 groups on the basis that, for example, any dinoflagellate is likely to be more like 

 another dinoflagellate in its ecological requirements than a diatom. 



There is a second possibility; that is, within each major taxonomic group there 

 may be a wide variation in photosynthetic efficiency or ecological requirements Irom 

 one species to the next. Thus, particular species of diatoms may be ecologically 

 almost equivalent to particular species of dinoflagellates and dilTercnt from other 

 diatoms as far as photosynthetic effectiveness goes. Thus, replacement ol a particular 

 diatom by a dinoflagellate might not result in a measurable change in the relationships 

 discussed, but replacement of the same diatom by another might --' '" '-^^ 

 change Such adaptive radiation within the major groups .s very probable, but data 

 apparently do not exist to permit this question to be decided. There seem to fK no 

 comparative studies of the genera which were prominent in the tank populations 



