Table 15. Comparison of several iron sources for the 



growth of Ceratophyllum demursum in a synthetic 

 culture medium (0.56 ppm Fe provided from each 

 Fe source) . 



Fe 

 source 



Oven-dry plant 

 wt (g/1)* 



pH of medium 

 at harvest 



Fe citrate, auto- 

 claved separately 



FeEDTA, auto- 



claved separately 



FeEDTA, autoclaved 

 with the medium 



0.008 



0.833 



0.843 



5.72 



7.00 



6.95 



FeEDDHA, auto- 

 claved separately 



FeEDDHA, autoclaved 

 with the medium 



1.315 



1.373 



7.14 



7.10 



* Each value is an average of results from duplicate 

 cultures. 



From experience on this project, it is difficult to 

 generalize on the response of macrophytes to a specific 

 concentration or source of iron. Even the addition of 

 0.56 ppm iron as FeEDDHA has not always provided adequate 

 iron. Also, FeEDTA sometimes is as suitable an iron 

 source as is the EDDHA complex. The most satisfactory 

 results have been obtained by adding 0.56 ppm iron as 

 FeEDDHA when the culture medium is prepared and then a 

 second and often a third increment of 0.28 ppm iron after 

 growth is initiated. The supplemental iron is added 

 aseptically when the red color of the FeEDDHA complex 

 has nearly disappeared, usually 7 to 10 days into the 

 culture period. A third addition may be necessary if the 

 red color again disappears. 



44 



