Nitrogen cycling in microbial mat communities: The quantitative importance of N-fixation and other sources of N for primary productivity

Abstract

Although N-fixation has been assumed to contribute substantially to the overall N requirements of primary production in benthic microbial mat communities, few quantitative studies have been undertaken. Several factors have contributed to the lack of quantitative data including: 1) pronounced temporal variability in rates of N-fixation (which necessitate rate measurements over entire diel cycles), 2) difficulties in relating rates of nitrogenase activity (acetylene reduction) to actual N fixed (due to possible natural variations in this ratio, documented in other systems; Bothe, 1982), and 3) differences in methodologies used by various authors to assay N-fixation. These restraints on the acquisition of quantitative N-fixation data, as well as comparable restraints on obtaining reliable estimates of carbon fixation in these communities (Revsbech et al. 1981), result in some uncertainty as to the importance of N-fixation in supporting primary productivity in microbial mats.