Saxifraga caespitosa Cochlearia oflicionalis arctica 



Saxifraga punctata Cetraria nivalis 



Ranunculus nivalis Cetraria simmonsii Krog. 



Salix sp. Cetraria richaidsonii (Hook.) 



Ranunculus pygaeus Polygonum acutiflora 



Saxifraga hieracifolia Moss from Nuwuk Pond 



Table XXIV. The results of acetylene reduction nitrogen fixation 

 measurements for the terrestrial Banow tundra. 



Ethylene produced/hr Equivalent N lixed/br 

 (fi mole X JO-'J (/xg-at x 10-^) 



Site 2 

 Control plots and quadrats 24 July 



2.33 

 2.05 

 1.72 

 1.90 

 1.09 



0.09 

 0.00 

 0.00 



0.00 

 0.00 



Note: All experiments were carried out on S-ctn x 3-cm squares taken from 0.01 m^ 



core. Blank samples (without added acetylene) were run for each core, with nega- 

 tive results, "n confirmation for these results will be available for selected sam- 

 ples. 



Table XXV shows plants which yielded positive results, including three species of lichens, 

 two of which still await identification. Blue-green algae, where present, appeared to be important 

 contributors to the tundra nitrogen budget, and fixation was also associated with several other 

 plants. It is important to realize that no claim is made here for nitrogen fixation by the plants 

 themselves, but only that active nitrc¥;en fixation was associated with these plants. The organisms 

 responsible may be bacteria associated with root or leaf nodules, bacteria or blue-green algae in 

 physical association with the plants, or even such organisms inadvertently introduced with the 

 plant into the experimental vessels. The nitrc^en-15 results, which will involve separate analyses 

 of enrichment in the roots, leaves and stems, may yield further information. From the ecological 

 point of view, it is significant to know that there is nitrc^en input from the atmosphere in associa- 

 tion with these plants. 



Based on the information obtained on the intensive site plots, nitrogen fixation would appear 

 to be a major input into the tundra nitrogen cycle in this area. A rate of approximately 2 ^g-at/m^ 



hr may account for a large proportion of the total nitrogen assimilated by the photosynthetic organ- 

 isms. Further information on seasonal variations and more intensive work on the variability of 



such fixation rates on the tundra surface would now be desirable. 



57 



