234 V. Alexander et al. 



TA BLE 5-9 Nitrogen Content of Vascular Plants in Tundra 

 Ponds, 1972* 



*Means of duplicates, expressed as % dry wt. 

 FACTORS CONTROLLING ROOTED AQUATIC PLANTS 



Introduction 



Numerous observations have shown that the stands of Carex and 

 Arctophila in the ponds are the most productive of all the stands measured 

 at Barrow (Bunnell et al. 1975). In addition, the two stands appear quite 

 different because the terrestrial plants include standing dead leaves while 

 the pond plants include only living leaves. Particularly after a number of 

 years of low lemming density, the tundra appears brown for most of the 

 growing season while the pond margins are always green. At the time of 

 maximum standing crop on the tundra, the leaf area index ranges between 

 0.6 and 1.0 for living matter and from 0.0 to 1.5 for standing dead matter 

 (Bunnell et al. 1975). Obviously the standing dead material is quite rapidly 

 felled or otherwise removed in the ponds but the exact mechanism is 

 unknown. Most likely the constant immersion'of the stem bases increases 

 the decomposition rate of this part of the plant. Another possibility is that 

 the leaves growing in the pond are mechanically disrupted in some way by 

 the formation of the ice. This process certainly appeared important in the 

 destruction of Carex leaves that had overwintered twice (Chapter 8). 



Carex in the ponds also has the advantage over the terrestrial Carex 

 in that the ice preserves some green tissue. In the spring, the Carex in the 

 ponds will have 5 or 6 cm of green tissue on each leaf that can begin 

 immediate photosynthesis. We cannot quantify the importance of this but 



