Spatial and temporal distribution of algae in soil crusts in the Sahel of W Africa: Preliminary results

Abstract

As part of an international project dealing with genetic diversity in wild forage species of the Sahelian Zone, a preliminary investigation of soil algal crusts in highly degraded environments was made. Soil sealing and the formation of crusts belong to the complex mechanisms of desertification processes. The kinds of soil algae present in the crusts and their temporal dynamics through the seasons are of relevance for the understanding of these processes. Surface crust samples from two wet and two dry seasons were examined for their algal flora by culturing and microscopy, in order to assess the role of algae in such processes. At least two different types of crusts were distinguished: dark crusts with a high algal contribution, dominated by filamentous blue-green algae (cyanobacteria), and light crusts with a far lesser algal contribution. The development of cyanobacterial crusts over two years suggests a seasonality, with a codominance of coccal green algae during the dry seasons. On light soils, a gradient was also apparent in the algal flora from sealed to sandy patches. In long-term development of fast changing arid ecosystems such as the Sahel, soil algae might prove a useful bio-indicator in screening for desertification and revegetation.