454 



W. T. Edmondson 



by a factor of as much as 5 (Fig, 1). It is interesting that the difference in order of 

 addition of nitrogen and phosphorus in Tanks 3 and 4 in Experiment 1 appears to 

 have made a difference in the subsequent behaviour of the populations. Addition 

 of the large amount of phosphate in Tank 3 was not followed by an increase, whereas 

 in Tank 2, a smaller amount of phosphate had doubled the rate. In Tank 4, nitrogen 

 was added first and the subsequent addition of phosphorus had a further effect. The 

 refertihzation of Tank 3 on August 25 was followed by an increase in photosynthesis. 



lO 

 AUGUST 



Fig. 1. Gross photosynthesis, incident light and chlorophyll in the four tanks. Photosynthesis as 

 mg/l/day of oxygen produced, light as cal/cm^/day of visible light, and chlorophyll as (Jig/1. Note 

 that chlorophyll is plotted on a logarithmic scale. The first two sets of points in the top panel are 

 for bottles filled on July 2 before and after the first fertilization. The histogram at the right of the 

 top panel gives the relative frequency of the rates in the ranges shown. 



It was necessary to know whether removal of the population from the open water 

 to the tanks would have an effect aside from the effects of added nutrients. For 

 that reason, in Experiment 2, fertihzation with phosphorus was delayed for four days 

 after filling, and addition of nitrogen delayed another four days. Population density 

 and photosynthesis did not change significantly until after the second fertihzation. 



Fertilization was usually followed by an increase in population, but at first the 

 increase was not as great as that in rate of photosynthesis, suggesting that lack of 

 nutrients had been inhibiting the photosynthesis of the individual organisms. 



After the initial increase in the rate of photosynthesis following fertihzation, there 

 were large changes in the rate in all four tanks. The changes will be discussed in 



