158 F. S. Chapin III et al. 



inoids in Wyoming (Wallace and Harrison 1978). Thus, it appears that 

 the effects of low temperature upon allocation in tundra plants are in- 

 volved more with growth processes than with inhibition of carbohydrate 

 and nutrient transport. Data in support of this hypothesis are largely in- 

 ferential, and direct experimental evidence is needed. 



Roots are more strongly buffered against temperature variation 

 from one growing season to another than is the plant canopy, and shoot 

 growth increases more rapidly with increasing temperature than does 

 nutrient uptake. For these two reasons, in a warm growing season pro- 

 duction is greater and the demand for nutrients outstrips the slightly en- 

 hanced supply. The situation is aggravated by the asynchrony of shoot 

 production and nutrient uptake, the bulk of the nutrient uptake occur- 

 ring after shoot production is largely complete (Chapin and Bloom 

 1976). The asynchrony is demonstrated by a comparison of the 1972 and 

 1973 growing seasons (Table 5-4) and suggests the following hypotheses: 



1. In tundra communities, warm years will result in greater nutrient 

 deficiency than will cold years. Nutrient deficiency will be particularly 

 severe with respect to phosphorus because phosphorus absorption is 

 more strongly affected by temperature than is absorption of other 

 nutrients (Nielsen and Humphries 1966). The effect upon nutrient con- 

 tent of yearly temperature differences will be particularly pronounced in 

 tundra underlain by permafrost, where the temperature gradient is most 

 pronounced from the canopy to the bottom of the rooting zone. 



2. Changes as slight as 1 °C in air temperature above the plant can- 

 opy are sufficient to profoundly alter the nutritional status of plants. 

 Data from the Biome research area indicate the sensitivity of allocation 

 pattern to small changes in environmental parameters. Similar conclu- 

 sions were independently reached by Wielgolaski et al. (1975) in studies 

 of the Norwegian alpine. 



In summary, studies of carbohydrate allocation suggest that plants 

 of the coastal tundra at Barrow have compensated for the effects of low 

 temperature by allocating a large proportion of their biomass to nutrient- 

 absorptive and belowground storage tissues. The high TNC levels suggest 

 that growth of ungrazed tundra plants is not unduly carbohydrate-limited. 



CARBON COST OF PLANT GROWTH 

 Concepts 



The carbon fixed through photosynthesis can be converted to new 

 biomass, but there are certain energy costs of producing and maintaining 

 an increment of biomass that must be considered in order to understand 

 patterns of carbohydrate allocation. The rate of change in live biomass 



