determination of AN increases rapidly (Vedernikov, 1973), while with 

 higher contents, the high population density may have a negative 

 influence on photosynthetic activity of the phytoplankton . 



It was found (Fig. 9d) that for all temperature intervals, there 

 is a positive connection between the content of nitrates and the values 

 of AN. As the nitrates increased from the level of analytic zero to 3-5m 

 g'atom/£, the mean value of AN increased by a factor of 2-3. This 

 increase was statistically reliable. 



Rather high values of AN with practically zero content of nitrate 

 nitrogen resulted, apparently, from the presence of ammonia nitrogen in 



^max 



s./ /J /J.C 



NO3 + NO2, yg-atcm/£ 



Fig. 10. Maximum energy effectiveness of photosynthesis (Q^^^ %) 

 and concentration of oxidized forms of nitrogen { pg 'atom/ Ji) for each 

 station. Stations with primary production of: 1, < 2; 2, 2-10; 

 3, > 10 mg C/m-^«day. 



the water. It is possible that this form of nitrogen and certain dis- 

 solved organic substances containing the amino group act as a buffer, 

 preventing the extreme degree of nitrogen starvation of phytoplankton 

 when the nitrates in the water are completely exhausted (Thomas, 1970). 



The relationship between AN^^ and phosphates is weaker than the 



relationship with nitrates (Vedernikov, 1976). This confirms once more 



that nitrogen limits primary production more strongly than does 

 phosphorus. 



Data on 

 nutrition ag 

 regulates th 

 level of fun 

 same conclus 

 maximum valu 

 of oxidized 

 layer: the 

 is positivel 

 (Fig. 10). 



the variation of AN^p^ with the conditions of mineral 

 ree with the assumption that mineral nutrition not only 

 e structure of the photocenosis , but also determines the 

 ctioning of the individual photosynthesizing units. The 

 ion results from station-by-station comparison of the 

 es of effectiveness of photosynthesis with the concentration 

 nitrogen at the same depths--at the bottom of the photic 

 effectiveness of photosynthesis upon threshold illumination 

 y related to the concentration of nitrates and nitrites 



248 



