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Temperoture, °C 



FIGURE 4-5. The response of photosyn- 

 thesis ( — ) and dark respiration ( ) to 



temperature in Dupontia fisheri (D.f.), Po- 

 gonatum alpinum (P.a) and Calliergon sar- 

 mentosum. (C.s.). The curves for D. fisheri 

 are from the field (o) and laboratory (m). 

 The curves for P. alpinum and C. sarmen- 

 tosum are for field-grown samples meas- 

 ured in a field laboratory. (After Tieszen 

 1973; unpubl.; Oechel and Collins 1976.) 



drier, temperatures were above 10°C at midday 73% of the time and 

 reached as high as 30 to 35 °C. However, in 1974 tissue temperatures 

 above 20 °C were seldom measured (Oechel 1976, Oechel and Collins 

 1976). The broad temperature responses of arctic bryophytes make them 

 well adapted to the wide range of tissue temperatures encountered in the 

 Arctic. However, at least in the case of Dicranum, simulation modeling 

 indicates that the relatively high values for temperature optima for pho- 

 tosynthesis result in a seasonal depression of photosynthesis of about 

 25<Vo (Oechel et al. 1975). 



