Nitrogen fixation by microbial crusts from desiccated Sahelian soils (Niger)

Cyanobacterial crusts developing on the sandy and loamy soils of fallow lan ds in the Sahel (Niger) were investigated for their potential to fix nitrog en. Three sites were selected in this and environment, differing in sedimen t type and species composition. In the sandy sites heterocystous nitrogen-f ixing cyanobacteria were present, whereas the loamy site did not contain su ch species. All sites showed light-dependent nitrogenase activity, starting within 2 h after re-wetting of the desiccated crust samples. Inhibition of photosystem II caused a decrease of nitrogenase activity in the samples wi th heterocystous cyanobacteria, but was stimulatory in the non-heterocystou s crust. The results suggest that cyanobacterial crusts may be important fo r the improvement of the soil by enriching it with nitrogen. (C) 2001 Elsev ier Science Ltd. All rights reserved.