Factors affecting productivity in fertilized salt water 



461 



In the present work a number of enrichments were made with nutncnts added to 

 the bottles, not the whole tanks, in order to determine the degree to wh.ch these sub- 

 stances might be hmiting photosynthesis. 



For example, on July 29 the population of Tank 2 was highly responsive to enrich- 

 ment with phosphate and nitrate, while that of Tank 4 showed no response (Tabic II) 

 The results are mterpretable on the basis that Tank 4 had previously been more 

 heavily fertiUzed, relative to Tank 2, and the population of the former tank was not 

 inhibited by lack of nutrients. The phosphate concentration in the two tanks before 

 enrichment was 0-13 and 0-46 /xg at/1 of P, respectively. 



Table II 

 Results of enrichment with nutrients, July 29-31 1947. The rate of photosynthesis 

 is tabulated for bottles enriched with phosphate, nitrate, both, and nothing 



Photosynthesis hi 

 Tank 2 Tank 4 



Added : 



O (control) 0-6 mg/l/day 0-9 



P(0-5^g/l) 0-7 0-9 



N(80ng/1) M . 0-9 



PandN 1-3 9 



PHOTOSYNTHESIS AND PHOSPHATE ASSIMILATION 



Previously, it was demonstrated that there was a close correlation between amount 

 of oxygen produced by a population and amount of phosphate removed from the 

 water (Edmondson and Edmondson, 1947). This relation was investigated further 

 in the present work. In Experiment 3, phosphate assimilation was measured in a 

 manner analogous to that by which photosynthesis was measured, by measuring the 

 phosphate concentration in suspended bottles. In most series, phosphate increased 

 in the dark bottle and decreased in the light bottle. By subtracting the change in the 

 dark bottle from that in the Hght bottle, one obtains a gross phosphate assimilation 

 which, in most cases, is a negative number, indicating decrease of concentration in 

 the water. Similarly, the changes in particulate phosphorus were measured. The 

 data on phosphorus were taken by Dr. David M. Pratt, who made a detailed study 

 of the phosphorus cycle in Experiment 3 (Pratt, 1950); his paper should be con- 

 sulted in connection with this section. It is of interest to compare assimilation of 

 phosphorus with the measurements of photosynthesis. 



The phosphate which appears as net change in the dark bottle is most likely released 

 by bacteria and animals, not by intact algae. It would seem, therefore, that in addition 

 to comparing the gross changes in phosphorus with gross photosynthesis, it would be 

 meaningful also to study the relation between gross phosphate assimilation and net 

 photosynthesis, where the latter is the rate of change of oxygen in the light bottle, 

 and is equivalent to the quantity (gross photosynthesis-respiration). That it is 

 reasonable to study this relation is shown by considering the fact that carbon dioxide 

 but not phosphate is freely released by algae in the dark bottle. Unfortunately, with 

 present techniques, a true measurement of net photosynthesis is not obtained, since 

 a large population of bacteria develops on the glass surface of the bottle. Thus, the 

 rate of respiration and presumably phosphorus metabolism is higher in the bottle 



