Nitrogen fixation in soils of Truelove Lowland, Devon Island, Northwest Territories

Abstract

Biological nitrogen fixation was studied on Truelove Lowland, Devon Island, N. W. T., in three different habitats. Raised beach ridges, resulting from postglacial uplift, form well-defined xeric habitats, which are dominated by dwarf shrubs and cushion plants. Hummocky sedge meadows with associated mosses and forbs comprise the second intensively studied habitat. Waterlogged wet sedge meadows with moss were studied less intensively.Nitrogen fixation was estimated using acetylene-reduction assay. Incubation temperatures were moderated by burying the jars in soil pits (10 cm) on site.Available nitrogen was determined by microkjeldahl analysis of KCl soil extracts.Symbiotic nitrogen fixation by vascular plants is nil on Truelove Lowland. One lichen species, Peltigera aphthosa, reduced acetylene (5.1 μμmol∙mg−1∙h−1). Nostoc commune, a prominent blue-green alga on meadow soils, reduced acetylene at a rate 10 times that of P. aphthosa. An estimated 30 and 7 mg N∙m−2∙year−1 was fixed by bacteria and soil algae in beach ridge soil in 1971 and 1972 respectively, and 380 and 120 mg N∙m−2∙year−1 was fixed in meadow soils in the same years.