146 F. S. Chapin III et al. 



FIGURE 5-4. Simulated seasonal biomass pattern of 

 different plant parts o/Dupontia fisheri tillers of differ- 

 ent ages. (After Stoner et al. 1978d, Lewis, unpubl.) 



ground growth behind aboveground growth is common to temperate and 

 other arctic graminoids and presumably is a consequence of programmed 

 reallocation of resources from one plant part to another (Evans et al. 

 1964, Auclair et al. 1976, Callaghan 1976, Chapin et al. 1980). The soil 

 reaches maximum temperature later in the season than does air, and this 

 may have further selected for asynchrony of above- and belowground 

 growth. Simulations suggest that rhizome weight in flowering tillers con- 

 tinues to decline through the entire season, coincidental with the growth 

 of the culm and inflorescence. Although the overall seasonality of rhi- 

 zome growth is probably genetically programmed, the absolute growth 

 rate is subject to environmental modification. In contrast to the temper- 

 ate graminoids investigated, Dupontia is capable of active rhizome 

 growth at soil temperatures at least as low as 4°C (McCown 1978). 



I 



