168 



F. S. Chapin III et al. 



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5 10 15 20 25 



Mean Soil Temperature, °C 



30 



FIGURE 5-11. Phosphate absorption ca- 

 pacity fVmaxJ of roots grown and measured 

 at 5 °C in relation to the July mean soil tem- 

 peratures of the site. 1) Eriophorum an- 

 gustifolium, Barrow, Alaska; 2) Dupontia 

 fisheri, Barrow, Alaska; 3) Carex aquatilis, 

 Barrow, Alaska; 4) Eriophorum scheuch- 

 zeri, Fairbanks, Alaska; 5) Scirpus micro- 

 carpus, Los Gatos, California; 6) Eleochar- 

 is palustris, Fairbanks, Alaska; 7) Carex 

 aquatilis. Circle Hot Springs, Alaska; 8) 

 Eleocharis palustris, Corvallis, Oregon; 9) 

 Scirpus olneyi. Thousand Palms, Califor- 

 nia. (After Chapin 1974b.) 



tial nutrient develop a high capacity to absorb that nutrient (Hoagland 

 and Broyer 1936, Cole et al. 1963). For example, individuals of Carex 

 with a high phosphate status had lower capacities for phosphate absorp- 

 tion (Chapin and Bloom 1976). 



Soil oxygen, which appears to be a major determinant of plant dis- 

 tribution at Barrow, has a direct impact upon absorption of both essen- 

 tial and toxic nutrients. Graminoids have well-developed aerenchyma 

 that transports sufficient oxygen to the rooting zone to create an aerobic 

 zone around each root (Barsdate and Prentki, unpubl.). Many dicotyle- 

 dons lack aerenchyma and are excluded from the wetter habitats. The 

 oxygen in the aerobic soil zone around a root decreases the solubility of 

 toxic heavy materials. In spite of this relatively aerobic rhizosphere, 

 graminoids absorb sufficient iron and manganese to reach levels that 

 would approach toxicity in crop plants (Ulrich and Gersper 1978). No- 

 thing is known about the influence of these minerals on tundra plant 

 growth. 



The uniform distribution of nutrient absorptive capacity along 



