Nitrogen fixation by Nostoc colonies in terrestrial environments of Aldabra Atoll, Indian Ocean

Abstract

The rates of acetylene reduction were compared in situ for six different types of terrestrial and semi-aquatic Nostoc colonies on Aldabra as an indication of their rates of nitrogen fixation. The rates per unit chlorophyll a were all rather similar during standard assays in mid- to late morning, with a mean rate of C2H4 production for all experiments of 0·0388 nM C2H4 μg chi a−1 min−1. The rates for Nostoc colonies were at least ten times those for mature cushions of Tolypothrix byssoidea. Marked variation in rates of C2H4 production occurred throughout the day, with the peak rates occurring in early afternoon. Three of the types of Nostoc were re-wetted in the laboratory one year after they had been dried. All showed high rates of C2H4 production after a lag of up to one day. The lag was much shorter in a population of N. commune freshly collected in England. It is suggested that colonies of Nostoc are especially suitable for comparative studies of nitrogen fixation in different parts of the world, in view of the ease with which viable colonies can be stored for later extraction of chlorophyll or laboratory experiments.