Control of Tundra Plant Allocation Patterns and Growth 



151 



TABLE 5-2 



Variability of Chemical Composition, Pro- 

 duction, and Photosynthetic Potential in 

 Leaves and Rhizomes of Dupontia fisheri 

 Along a Moisture-Nutrient Gradient 



Source: Calculated from Tieszen (unpubl.). 



simulations suggest a similar conclusion, i.e. that an increased photosyn- 

 thetic rate, and hence increased TNC availability, would increase pro- 

 duction at Barrow but that this TNC limitation of growth is less marked 

 than is limitation by nutrients (Miller et al. 1976, 1979). It appears that 

 although arctic tundra plants grow in a low radiation environment, car- 

 bohydrate availability does not unduly limit growth. 



In mature shoots o{ Dupontia storage polysaccharides constitute the 

 bulk of the TNC pool (Figure 5-5) (McCown 1978), in contrast to the 

 predominance of sugars observed in other arctic and alpine species 

 (Mooney and Billings 1960, Fonda and Bliss 1966, Warren Wilson 

 1966a). These reserves may be important for periods of intensive grazing. 

 Although soluble carbohydrates are generally less than 15% of dry 

 weight in Barrow graminoids, these levels are nonetheless high in com- 

 parison with temperate plants, and may contribute to the frost tolerance 

 (Weiser 1970) that allows arctic plants to survive subzero temperatures at 

 any time during the active growing season (Sdrenson 1941). In Dupontia 

 the rhizome is the largest compartment for TNC storage. From 40 to 

 65% of the total TNC is located in the rhizome throughout the year 

 (Table 5-1). Fructosans rather than starch are the main storage polysac- 

 charide in arctic (McCown 1978) and cool temperate (White 1973) 

 grasses. 



Tissue age strongly influences both the types and amount of carbo- 

 hydrate present. In new roots and in the rhizomes and stem bases of 

 young tillers, monosaccharides are the predominant carbohydrate, 

 reaching concentrations as high as 40% dry weight (Shaver and Billings 



