Thus, the conditions of mineral nutrition of phytoplankton 

 influence production, acting not only on the structure of a community, 

 but also on the intensity of functioning of the individual organisms. 



Temperature . The study of the influence of temperature on the 

 production characteristics under natural conditions is greatly hindered 

 by the fact that temperature in nature is positively correlated with 

 illumination and negatively correlated with the concentration of 

 nutrient salts and, therefore, influences photosynthesis not only 

 directly but also indirectly. Also, in determining production by the 

 radiocarbon method, the effect of temperature may depend not only on the 

 intensity of photosynthesis, but also on the relationship between 

 photosynthesis and resoiration, since these two processes cannot be 

 distinguished by the ^^C method. The close interrelationship of the 

 temperature factor to light and the effect of nutrients has resulted in 

 the fact that most authors analyze this factor in combination with the 

 others. 



It has been established that the light adaptation of algae is 

 closely related to the temperature conditions. Experiments carried out 

 under semi laboratory conditions have shown that "dark" phytoplankton, 

 living in the lower portion of the euphotic zone, is adapted to lower 

 temperatures than "light" phytoplankton. Furthermore, it is thought 

 that adaptation to low levels of illumination is an apparent phenomenon, 

 while in actuality the corresponding light curves of photosynthesis are 

 natural for algae living at low temperatures. 



Experiments with both cultures and natural populations have shown 

 that algae appertaining to various systematic groups differ as to 

 temperature options of photosynthesis and rates of cell division. A low 

 temperature optimum is observed in diatoms, a higher optimum in green 

 algae (Eppley, 1972). The higher the temperature optimum of the algae, 

 the more intensive its photosynthesis and the higher the rate of 

 division of which it is capable. The position of the temperature 

 optimum of photosynthesis and the growth of algae are influenced much 

 more by temperature conditions of growth and habitat temperature than by 

 taxonomic composition (Barker, 1935; Braarud, 1961; Ichimura, Aruga, 

 1964, 1965). Below the temperature optimum, there is a relationship 

 between the rate of assimilation of COp and the temperature which is 

 near exponential (Heath, 1972). In cultures of various planktonic algae 

 grown at 20°C, the ordinary values of temperature coefficient Qj^q = 2-3 

 are characteristic for broader temperature ranges (20° or 30°C). 

 However, for narrower temperature ranges (5-10°C), the values of Qiq are 

 more varied, for example for green algae from 1.3 to 4.8, higher at low 

 temperatures than at high temperatures (Rabinovich, 1959, page 39). 

 This apparently results from the fact that in the area of low 

 temperatures they control the dark reactions which are the main factor 

 limiting the rate of the entire process of photosynthesis (Heath, 1972, 

 page 201). At higher temperatures, dark reactions occur more rapidly, 

 Q^Q decreases, the light energy absorbed by the chloroplasts is not 

 sufficient for assimilation of additional quantities of CO2, and 

 photosynthesis begins to be limited by light, even when its intensity is 

 quite high. 



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