positive relationship has been found between the mean zonal values of 

 primary production and the content of phosphates, nitrate nitrogen and 

 silica in the upper 100-meter layer; the correlation coefficients are 

 +0.68; +0.83 and +0.88 (Maksimova, 1972). In the more productive waters 

 of the near-antarctic region of the southwestern Atlantic, the 

 correlation coefficients between phytoplankton production in the surface 

 layer and the content of phosphates and nitrates is much lower: +0.42 

 and +0.44 (Kabanova et al., 1974a ,b). 



In regions of low productivity, where the concentration of 

 nutrients approaches analytic zero, the variation of production with the 

 content of these elements is difficult to trace due to the significant 

 measurement errors. 



Extensive materials collected in the tropical Pacific, Indian and 

 Atlantic Oceans were used (Fig. 9a) to compare the concentration of 

 nitrates and primary production at the surface (> 1300 stations) and at 

 the depth of maximum AN, i.e., in the layer of optimal illumination (200 

 stations) (Fig. 9b). The relationship between the values of primary 

 production and concentration of NO3 is described in log-log coordinates 

 by an S-shaped curve. Since at low concentrations of nitrogen, its 

 reduced forms play a significant role in the mineral nutrition of algae 

 (Thomas, 1970), determination of the concentration of NO2 and NH^ would 

 result in some straightening of the initial slope of the curve, and it 

 might be described by the Michael is-Menten equation. The relationship 

 between the concentrations of nitrate nitrogen and photosynthesis at the 

 level of optimal illumination is described by practically the same curve 

 as for the surface. 



The effect of nutrients on production can be represented in two 

 ways. In the opinion of some authors (Fedorov, 1970; Koblentz-Mishke et 

 al . , 1975), under favorable conditions of mineral nutrition, as a result 

 of structural changes in the phytoplankton community, a denser 

 population of phytoplankton exists than in the poorer regions, more 

 completely absorbing solar energy and using it for more intensive 

 summary photosynthesis. Other authors (Baslavskaya , 1961; McAllister et 

 al., 1964; Thomas, Dodson, 1972; Kabanova et al., 1974a ,b) believe that 

 an improvement in the conditions of mineral nutrition influences 

 primarily the effectiveness of the action of the photosynthetic 

 apparatus of each individual cell. 



The reality of the first mechanism is beyond doubt. This is 

 indicated by the positive relationship between the concentration of 

 nutrients and the abundance of phytoplankton (Semina, Tarkhova, 1970) 

 and the concentration of chlorophyll (Taniguchi, 1972; our data--Fig. 

 9c). 



The second mechanism has been confirmed by data on the AN under 

 various conditions of mineral nutrition. 



Poor mineral nutrition conditions for phytoplankton may result in a 

 decrease in the AN: this is shown in enrichment experiments with 

 natural populations and cultures of planktonic algae. For natural 

 populations of phytoplankton, inhabiting waters with a high content of 



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