NITROGEN-FIXATION BY CYANOBACTERIA ASSOCIATED WITH MOSS COMMUNITIES IN SCHIRMACHER-OASIS, ANTARCTICA

N-2-fixation by cyanobacteria growing in association with moss communities from Schirmacher Oasis (lat 70 degrees 45' S; long 11 degrees 45' E), Antarctica, was investigated. Moss samples were collected from four sites differing in moisture regime: close to a lake (A), near a meltwater stream (B), a hilltop (C), and a nunatak (D). Cyanobacteria species diversity and density were variable in these sites. The maximum number of species were observed at site B, the minimum, at site D. Jaccard coefficient analysis showed that none of the sites exhibited more than 55% similarity. Acetylene reduction was highest in samples at site D, where the relative proportion of N-2-fixing species was highest, and lowest at site B, which exhibited the lowest proportion of N-2-fixing species. The observed acetylene reduction was not due to heterotrophic N-2-fixing microbes. Results suggest that N-2-fixation is primarily performed by diazotrophic cyanobacteria, and rates are variable depending upon cyanobacteria species diversity and density. Soil properties below the moss community were modified in comparison to soil where cyanobacteria growth was absent.