Dinitrogen Fixation (Acetylene Reduction) in High Arctic Sedge Meadow Communities

Abstract

Dinitrogen fixation rates were investigated, using an acetylene reduction technique, in intact soil cores of sedge meadow communities at two high arctic sites on Ellesmere Island: Alexandra Fiord (78055'N) and Sverdrup Pass (79?10'N). Acetylene reduction activity (ARA) showed increasing rates from snowmelt until late July, followed by a decline in the late growing season. The majority of ARA occurred in the upper 5 cm of the soil. Acetylene reduction activity on the soil surface constituted 35 to 65% of seasonal mean ARA. Blue-green algae (especially Nostoc spp.) were considered the major N2-fixing agents in the studied sites. There was little difference in ARA between Sverdrup Pass and Alexandra Fiord, despite differences in herbivore utilization; Alexandra Fiord was a nongrazed lowland, while Sverdrup Pass was heavily grazed by muskoxen. In the Alexandra Fiord meadows, ARA was equivalent to fixation rates of 65 to 104 mg N m~2 yr~1, and in the Sverdrup Pass meadows to 90 mg N m~2 yr1. At Alexandra Fiord, dinitrogen fixation was estimated to account for 65 to 80% of the total nitrogen input to the sedge meadow systems, with the balance coming from precipitation.