182 



F. S. Chapin III et al. 



O 



Temperoture, °C 

 4 8 12 



4 

 8 



12 



16 



20 



24 



28 



Permafrost 



FIGURE 5-20. Patterns of root distribution of Dupontia fisheri (D.f), 

 Carex aquatilis (C.a.) and Eriophorum angustifolium (E.a.) at peak 

 season. 



chronous in Carex and Eriophorum than in Dupontia (Mattheis et al. 

 1976), suggesting that shoots of Dupontia might be able to regrow more 

 rapidly following grazing than would shoots of the other two gram- 

 inoids. However, in the ungrazed situation earlier canopy development 

 by Carex and Eriophorum may give these two species a more favorable 

 carbon balance that in turn allows them to invest in new structures, par- 

 ticularly roots and rhizomes, to a greater extent than can Dupontia. 



The interspecific differences in growth and allocation patterns for 

 the three species are more pronounced below ground than above ground 

 (Shaver and Billings 1975), suggesting that at the Biome research area 

 competition is more intense and niche differentiation more clearly deline- 

 ated in soil than in air. Nutrient and oxygen concentrations, pH and 

 temperature all vary substantially with depth. The three principal gram- 

 inoid species have strikingly different rooting patterns and exploit differ- 

 ent depths (Figure 5-20). 



Roots of Dupontia are concentrated in the top 5 cm of the soil where 

 phosphate and potassium are most abundant and where temperature and 

 aerobic conditions are most favorable for absorption (Shaver and Bill- 

 ings 1975). Eriophorum has thin annual roots that grow vertically 

 downward following the seasonal thaw (Bliss 1956, Shaver and Billings 

 1975). At the freeze/thaw interface, phosphorus may be highly available 

 (SaebcT 1969). The disadvantages of the deep-rooting habit are that soils 

 are colder and less aerobic and that deep roots are locked in frozen soil 



