242 



V. Alexander etal. 



1 — I — I — I — I — I — I — r 



0.028 



J I I I L 



J I I I \ L 



8 12 16 20 24 



NH4 Concentration, ^g-at liter 



28 



-I 



32 36 



40 



FIGURE 5-38. Uptake of ammonia by Carex roots at different 

 concentrations of ammonia. (After McRoy and Alexander 

 1975.) 



The NHs-^^N that was taken up by the roots quickly moved to the 

 leaves. In the same experiment described above for roots, the leaves also 

 quickly became labeled. The K„ax was 0. 1 56 Mg N (^g of plant N) " ^ hr " ^ 

 and the K was 56 Mg liter '. This, of course, represents a transport from 

 the roots. No ammonia was taken up by the leaves and stem and no '''NH3 

 was lost from the plant by secretion. Thus, these results suggest that Carex 

 plants obtain most of their nitrogen by means of ammonia absorption 

 through the roots. This agrees with data from submerged plants in 

 freshwater (Toetz 1971, 1973, McRoy and Goering unpublished 

 observations). 



Conclusions 



In the Barrow ponds we studied, the most important primary 

 producer was a sedge, Carex aquatilis. Adaptations, such as the ability to 

 photosynthesize and translocate carbohydrates at low temperatures, 

 enable this plant to virtually ignore the low temperatures and have as high 

 primary productivity as temperate plants. Despite their low stature, the 

 erect leaves of the rooted plants intercept nearly all of the low-angled solar 

 radiation (average of 25° on 21 June). 



The plants in the pond are actually more productive than Carex 

 aquatilis plants on the tundra. One reason for this is the lack of standing 

 dead leaves in the pond. Perhaps because of constant immersion, the dead 



