Site-to-site variations in nitrogenase activity in a subarctic black spruce forest

Abstract

An estimate of nitrogen fixation in terms of acetylene reduction was made at two sites in a subarctic black spruce (Piceamariana (Mill.) B.S.P.) forest to determine site-to-site variations. The work was initially done to provide base-line comparative data for the primary intensive site, and for a site preparatory to an experimental burn. The principal conclusions were that, in contrast with the Alaskan arctic coastal tundra, microtopographic variations were not associated with big differences in acetylene reduction. Lichens with nitrogen-fixing phycobionts were an important influence on the activity; however, a high overall proportion of the activity was attributable to the moss cover, at least in part because of associated cyanobacteria. Daily rates for June and July averaged 74, 119 and 109 μg C2H4•m−2•day−1, respectively, for the 3 years. In common with other high-latitude sites, moisture was the major factor controlling nitrogenase activity.