Control of Tundra Plant Allocation Patterns and Growth 155 



was allocated above and below ground in approximately equal propor- 

 tions (Figure 5-7). Rubus chamaemorus from Sweden had an allocation 

 pattern consistent with its deciduous habitat. During the leaf production 

 phase, virtually all the assimilated carbon was retained in the shoot, as in 

 the actively growing Dupontia shoot. As the season progressed, an in- 

 creasing proportion of the photosynthate was translocated below ground 

 (Figure 5-7). Clearly, the allocation patterns of these three species are 

 closely tied to their growth forms, phenological calendars, and locations 

 of storage. 



Environmental Influence upon 

 Allocation Pattern 



Environmental factors affect allocation pattern as well as the total 

 quantity of production . High root-to-shoot ratios of plants observed in 

 the field at the Biome research area (Dennis and Johnson 1970, Chapin 

 1974a, Dennis 1977, Dennis et al. 1978, Webber 1978) may indicate 

 greater environmental limitation upon shoot than root growth (Dennis 

 and Johnson 1970) or more likely reflects a genetically and environment- 

 ally controlled allocation of biomass to nutrient absorptive tissue 

 (Chapin 1974a), as observed in laboratory studies (Brouwer 1965, David- 

 son 1969). Low root temperature may indirectly result in a high root-to- 

 shoot ratio by decreasing rates of nutrient uptake, thus lowering the nu- 

 trient status of the plant, i.e. low root temperature and low nutrient 

 status may influence allocation through similar mechanisms (Patterson 

 et al. 1972, McCown 1975). Laboratory studies indicate that the increase 

 in root-to-shoot ratio resulting from an impoverished nutrient status 

 serves to increase nutrient supply and decrease nutrient demand, thus 

 compensating for the nutrient deficiency (e.g. Leonard 1962, Brouwer 

 1965). Direct field evidence for this comes from long-term fertilization 

 studies at Barrow, where after 10 years of fertilization, the root-to-shoot 

 ratio was reduced from 7:1 to 3:1 (Dennis 1977). McCown (1978) ob- 

 served that the root-to-shoot ratio of Dupontia was less affected by root 

 temperature than was that of the temperate grass Poa pratensis. A 

 relatively inflexible root-to-shoot ratio is typical of slowly growing 

 species (Grime 1977). 



When growth is strongly nutrient-limited, nonstructural carbohy- 

 drates accumulate to high levels (Leonard 1962) as observed in Dupontia 

 at the Biome research area (Shaver and Billings 1976, McCown 1978). 

 TNC levels are reduced, and shoot growth is enhanced by fertilization, a 

 further indication of the importance of nutrients in limiting production 

 in the tundra (McKendrick et al. 1978). 



The number of daughter tillers (VO's) initiated is positively correlated 



