1446 



PHOTOSYNTHESIS IN INTERMITTENT LIGHT 



CHAP. 34 



tain. It is conceivable, for example, that plants may produce more or- 

 ganic matter in 12 hours of illumination followed by 12 hours of dark rest 

 than they would in a uniform 24 hour illumination of the same intensity. 

 The same may happen when photoxidation phenomena lead to a gradual 

 inactivation of the photosynthetic apparatus (as may occur in an at- 

 mosphere poor in carbon dioxide, or in light of excessive intensity, or in the 



► irr < 2 



Light 



Fig. 34.5. The three intermittency factors (for equal light and dark periods). 

 Intensity and duration of illumination is shown by black areas; photosynthesis 

 by shaded area. 



presence of excess oxygen; cf. chapter 19). In this case, the inhibition of 

 photosynthesis has been found to grow autocatalytically, and it may be 

 possible to prevent it by inserting dark recovery periods at appropriate 

 intervals. 



Early in this chapter we also asked another question — whether the 

 energy conversion yield can be improved by intermittency (i. e., whether 

 the factor ist can become larger than unity). As far as enzymatic limita- 

 tion in alternating light is concerned, this question, too, must be answered 

 with a denial. To prove this we refer to equation (34.2). In weak 

 hght (when the light curve is linear), /3 = 2 and in = 0.5; thus ist = 1- 



