The abundance and diversity of legume-nodulating rhizobia and arbuscular mycorrhizal fungal communities in soil samples from deforested and man-made forest systems in a semiarid Sahel region in Senegal

Abstract

Exotic and native tree species have been widely used in the West Africa to reverse the tendency of land degradation. Although benefic effects have been reported on soil stabilization, a lack of information about their impact on soil symbiotic microorganisms still remains. This investigation has been carried out in a semiarid Sahel region and aimed to survey the abundance and diversity of natural legume-nodulating rhizobia (LNR) and arbuscular mycorrhizal (AM) fungal communities in soil samples from deforested and man-made forest systems. A genetically diverse LNR population is supported by the phylogenetic analysis, which clustered the isolates into three genera: Bradyrhizobium, Mesorhizobium and Sinorhizobium. The results showed that the man-made forest systems increased the LNR abundance and genetic diversity as well as the soil phosphorus and nitrogen contents. By contrast, strong modifications have been recorded in the characteristics of the AM fungal communities. The number of AM fungus taxa as well as the mycorrhizal inoculum potential (MIP) of soils decreased drastically in the man-made forest systems in comparison with the deforested land. In addition, the larger-spored AM fungi (Scutellospora and Gigaspora) were specifically found in soil samples from the deforested land. The displacement of larger-spored species was associated with a concomitant proliferation of small spored (Glomus) species. We conclude that man-made forestry can modify the soil symbiotic microorganisms and the results support the need for further adoption of management practices that could improve or sustain the development of herbaceous layers to promote the soil AM fungal communities.