Assessment of the importance of biological nitrogen fixation in the terrestrial ecosytem: Nitrogen fixation rates of Nostoc cyanobacterial mats in the Garwood Valley and at Cape Royds

Microbes with the nitrogenase enzyme on mosses and soils, particularly the cyanobacteria Nostoc, were examined to investigate the extent and magnitude of the nitrogen fixation process. Sample cores from continuous cover of Nostoc in the Garwood Valley and Cape Royds were collected and subjected to various experimental conditions and using the acetylene reduction technique (to determine nitrogen fixation) and gas chromatography (to measure ethylene gas) the nitrogen fixation process was determined from diverse habitats. Core samples were incubated in 500ml jars containing 1% acetylene gas for no longer than 12hours in sub, shade or dark conditions and gas samples were removed periodically and ethylene was determined. In experiments, Nostoc was subjected to 5 cycles of oscillating environmental conditions to determine quantitative fixation levels in Nostoc at different moisture levels and the effect of oscillating environmental cycles on nitrogen fixation. Fresh, dry and ash free sample weights and nitrogen content were determined. Temperature and pH measurements of soils, waters and plants were made at the study site. The effects of amendments on fixation rates was determined by measuring fixation on samples subjected to phosphate, trace elements, chemical residue of a smoke bomb, urine, trampling and cover with soil 1cm deep.