Control of Tundra Plant Allocation Patterns and Growth 169 



a. Eriophorum vaginatum 



10 20 30 



Distance from Tip, cm 







10 



FIGURE 5-12. Distribution of phosphate uptake rate along roots of 

 Eriophorum vaginatum (Chapin 1974a) and wheat (Bowen and Rovira 

 1967). 



graminoid roots (Chapin 1974a) reflects the lack of a well-defined root 

 hair zone (Chapin 1978), a consequence of the anaerobic soil conditions. 

 The maintenance of absorptive capacity along the entire length of Erio- 

 phorum vaginatum roots is a striking difference from temperate grasses 

 (Figure 5-12) and may be selected for by the moist soil environment, 

 where suberization to prevent water loss and consequent loss of absorp- 

 tion capability is disadvantageous. 



NUTRIENT ALLOCATION 



Seasonal Patterns 



Since nutrients are among the prime factors affecting carbohydrate 

 allocation, it is important to know how nutrients are allocated within the 

 plant and the factors that control this allocation. Graminoids at Barrow 

 begin the growing season with a small amount of overwintering green 

 material. Translocation of nutrients to these shoots presumably begins at 

 or before snowmelt, coincident with the initial carbohydrate transloca- 

 tion to shoots. Early in the season the nitrogen and phosphorus concen- 

 trations of aboveground tissues are quite high (Figure 5-13) and the 

 nitrogen-to-phosphorus ratio is relatively low. This suggests that a large 

 proportion of the tissue is actively growing and metabolizing and hence 

 has a high phosphorus requirement for membrane phospholipid and 

 phosphorylated intermediates. As leaves approach maturity, they devel- 

 op more structural material, as indicated by the seasonal increase in per- 

 centage calcium (Chapin et al. 1975). The increase in structural material 

 causes percent nitrogen to decline (Figure 5-1 3a), though the total above- 

 ground standing crops of nitrogen and phosphorus are increasing (Figure 

 5-1 3b). Phosphorus follows the same pattern as nitrogen. The net trans- 

 fer of nitrogen and phosphorus to shoots continues until 25 July, ten 



