32 THE ROYAL SOCIETY OF CANADA 



Nitrification 



By nitrification is meant the conversion of ammonia into nitrite 

 and nitrate. These processes are carried out in the soil by very 

 specialized groups of bacteria and it seemed of interest to determine 

 whether organisms of a like kind could be found in the sea-water 

 under examination. 



The only reference to work on these lines which I have been able 

 to find is in a paper by Thomsen quoted by Drew; ^ but this author 

 appears to have isolated his organisms from the bottom of inshore 

 waters. 



Each of the samples was inoculated into a 2 per cent solution of 

 ammonium sulphate in sea-water containing magnesium carbonate in 

 excess. Cultures were kept both at 28°C and at air temperature as in 

 the previous cases, but no growth appeared to take place and no trace 

 of nitrite or nitrate could be found in any of them after three months. 

 It cannot be taken from a single series of experiments that nitrifying 

 organisms do not occur even in the samples examined, still less that 

 they do not occur at all in the open sea. It is true that any normal 

 soil would have produced nitrate under the same conditions in a much 

 shorter period than three months, but these conditions may not be 

 suitable for the development of marine forms. Cultivation should be 

 tried in solutions of salts of ammonia other than the sulphate and of 

 different concentrations. The presence of organic nutrient material 

 in culture solutions may be necessary for marine nitrifying forms, 

 if such exist, though it is injurious to soil forms. 



The question of the occurrence of nitrifying organisms in the 

 sea is of considerable interest in its bearing on that of the form in 

 which marine plants absorb their nitrogen. Recent work has shown 

 that land plants can assimilate nitrogen from ammonium salts direct, 

 though normally they are converted into nitrate by nitrifying bacteria 

 before assimilation. If marine plants require their nitrogen in the form 

 of nitrate, and no agency exists in the sea for oxidizing the ammonia 

 produced by the break down^of complex organic compounds, they 

 must depend upon nitrates produced by bacterial agency on land 

 and washed into the sea. This seems to be in the highest degree 

 unlikely for the result would be an accumulation of ammonia in the 

 sea and a gradual depletion of the store of nitrogen on land for the 

 benefit of life in the sea, except in so far as the loss from the land could 

 be made good by nitrogen fixation. 



'Thomsen, R., 1910. "Ueber das Vorkommen von Nitrobakterien in Meere." 

 Wiss. Meeresunters, Vol. XI. Kiel. 



