Organic Sources of Nitrogen for Marine Centric Diatoms 99 



species of algae corresponded only to the measured inorganic 

 nitrogen. 



Inorganic Sources of Nitrogen 



Addition of nitrite (or nitrate) to nitrogen-free medium did 

 not result in significant growth of flagellates or (9. Skeletonema 

 costatum, Rhizosolenia setigera, and Nitzschia serkita were in- 

 hibited somewhat by nitrite; the other clones grew as well on 

 nitrite as on nitrate. All strains grew in ammonia but the follow- 

 ing did not grow as well on ammonia or ammonia + nitrate as 

 on nitrate alone: Nitzschia seriata, Coccolithtts htixleiji clones 

 92-A and BT-5, Cyclotella nana (7-15), Cyclotella caspia, Skele- 

 tonema sp. (Men 5), and Coscinodiscus asteromphalus. Inhibition 

 by ammonia (or other compounds) was greater when the inocu- 

 lum was small or nitrogen-starved and less pronounced when 

 cultures were in dim light. 



Organic Sources of Nitrogen 



Studies of growth on organic sources are summarized in 

 Table 3. Values recorded are the maximum observed for each 

 species during the experiments. 



Glutamic acid was a poor source of nitrogen except for 

 Coscinodiscus asteromphaJus and Melosira sp. (0-8) which used 

 it as well as they did nitrate. Only three other species attained 

 as much as a tenth the yield on nitrate. Glycine, the other alpha- 

 amino acid, was not even as good as glutamate for most species, 

 but Coscinodiscus asteromphalus reached 69 per cent of the 

 yield on nitrate and Skeletonema costatum reached 18 per cent. 

 The amide glutamine was better than glutamate for all species 

 except Thalassiosira nordenskioldii (8% vs. 22%). Coscinodiscus 

 and Melosira grew as well on glutamine as they did on nitrate 

 or glutamate, and three other species, including two from the 

 Sargasso Sea, reached at least 30 per cent of the inorganic nitro- 

 gen yield. 



Urea was a better source than glutamine for most of the 

 neritic and estuarine species. Only Skeletonema (clone Men 5) 

 of the species isolated from the Sargasso Sea used it readily. 

 Growth of Chaetoceros lorenziamis probably depended upon de- 

 composition of the urea by bacteria. 



