TEMPERATURE EFFECT IN STRONG LIGHT 



1239 



to be valid, at least approximately, over a considerable range of tempera- 

 tures; whereas the log P = fO-/T) curves of the second group of investi- 

 gators (which also includes Warburg and Yabusoe) show practically no 

 straight section at all. The observations of van der Paauw on Hormidium 

 and Stichococcus also indicate continuous curvature of the logarithmic 

 temperature curve, even if this curvature is less strong than in Emerson's 

 curves. 



-0.8 - 



20,300 



21,000 



18,700 



18,400 



33 34 35 36 



\/T X 10^ 

 Fig. 31.11. Rate of photosynthesis as a function of temperature in the range 

 10-30° C. (after Craig and Trelease 1937). log P = f(l/T) for Chlorella. Figures 

 on curves are Ea values; curves 1-3 for HoO; curves 4—6 for D2O. Ordinate scale 

 given is for curve 3; curve 1 moved up 0.6; curve 2, up 0.2; curve 4, up 0.05; 

 curve 5, down 0.1; curve 6, down 0.25. 



In the region around 15° C, the activation energies found by most observers are in 

 approximate agreement (Ea = 10-12 kcal), although Barker gave Ea = 30 kcal for 

 diatoms, and Craig and Trelease, and Wassink and co-workers found for Chlorella 

 Ea = 20 and 18 kcal, respectively. Larger discrepancies are encountered below 10° 

 where the activation energies measured by some investigators were about the same as at 

 higher temperatures, whereas those found by others were up to 30 or even 40 kcal/ 

 mole. At 20-30° the Ea values sometimes were found to remain constant, and some- 

 times to decrease to as little as 5 or 8 kcal. 



Tamiya, Huzisige and Mii (1948) found that the temperature curve of the photo- 

 synthesis of Chlorella ellipsoidea can be interpreted, between 1° and 28° C, in the carbon 

 dioxide saturated state, by two consecutive reactions with activation energies of 6 and 

 27 kcal, respectively. This applied to measurements at pH 4.6 as well as at pH 7.0; 

 however, the first reaction was slowed down by a decrease in pH, while the second one 

 was unaffected by this change. 



