92 



P. C. Miller et al. 



(Relative Water Content) 



FIGURE 3-15. The relationships between relative 

 water content and leaf resistance and between 

 relative water content and leaf water potential for 

 Arctophila fulva (A.f.), Dupontia fisheri (DJ.), 

 Carex aquatilis (C.a.), Eriophorum angustifolium 

 (Em.), Potentilla hyparctica (P.h.), and Salix pul- 

 chra (S.p.). (After Miller et al. 1978b.) 



and Betula verrucosa (Jarvis and Jarvis 1963). The similarity of these 

 levels in different environments and species indicates that most vascular 

 plants maintain leaf water contents of more than 80 to 90% of their 

 turgid water content. The relation between water potential and water 

 content of the leaves also differed among the species in the Carex-On- 

 cophorus meadow (Stoner and Miller 1975). Arctophila showed the 

 highest rate of change of leaf water potential with a change in relative 

 water content (Figure 3-15). Eriophorum had the lowest. 



Leaf water potentials of grasses, sedges and soft-leaved forbs were 

 near bars with low transpiration rates during the night, even though the 

 sun is above the horizon 24 hours a day. These leaf water potentials were 

 higher than those of well-watered fell-field plants maintained in satu- 

 rated air in the laboratory, including Dryas integrifolia (-10 to -15 bars), 

 Saxifraga oppositifolia (-10 bars), and Dryas octopetala (-13 bars) 

 (Courtin and Mayo 1975). Soil water potentials within the root zone were 

 always greater than -0.5 bar. During the relatively warm, dry summer of 



