Effects of abiotic factors on nitrogen fixation by blue-green algae in Antarctica

Abstract

In situ nitrogen fixation (acetylene reduction) was compared for three types of free-living terrestrial blue-green algae at the Vestfold Hills, Antarctica. Rates of acetylene reduction by foliose mats of Nostoc commume and felts of Calothrix ranged between 0.82 to 211.2 p mol C2H4 μg chla-1 hr-1 at ground temperatures of -4 to 9°C. Mucilaginous colonies of N. sphaericum were less active than mats of N. commune. Diurnal studies on nitrogenase activity of N. commune indicated highest rates during the afternoons (1300 h). At 0°C under laboratory conditions, N. commune reduced acetylene at 19% of the rate of 20°C. Totally desiccated foliose mats did not reduce acetylene but activity commenced immediately the mats were wetted. Nitrogenase activity of Nostoc growing epiphytically on moss increased with temperature in moist samples but not when the vegetation was desiccated. The results indicate that maximal nitrogen fixation by Antarctic blue-green algae occurs during periods when microclimatic conditions are most favourable.