Nitrogenase activity of blue-green algae on seasonally flooded soils in Bangladesh

Abstract

Blue-green algal communities formed an extensive cover on soils at five deepwater rice-growing locations in Bangladesh during the month before the arrival of floodwater. The principal taxa wereAnabaena, Cylindrospermum, Lyngbya, Microcoleus, Nostoc, Prophyrosiphon notarisii, Scytonema mirabile andTolypothrix byssoidea. One of two locations studied after the floodwaters had receded also had an extensive cover, mainlyScytonema mirabile. Nitrogenase activity assayed at mid-day was from one to three orders of magnitude higher per unit area of community than bare soil. Nostoc showed higher activity than Tolypothrix, whether expressed per unit area or biomass. Whole field estimates of N2 fixed by blue-green algal communities during the pre-flood period ranged from 1.0 to 10.2 kg N ha−1. Much of this is probably not recycled until floodwaters cover the fields. However N2 fixed after floodwaters have receded is probably recycled rapidly due to ploughing.