Hydrologic Redistribution and Rhizosphere Biology of Resource Islands in Degraded Agroecosystems of the Sahel: A PIRE in Tropical Microbial Ecology By

In agriculture systems like the Sahel of West Africa, where climatic and anthropomorphic events have degraded the soil, the reduced crop yield can severely impact the economy of the country and the livelihood of its citizens. Furthermore, most farmers operate at the subsistence level and cannot afford chemical fertilizers to increase crop production. However, two common shrubs Guiera senegalensis and Piliostigma reticulatum, commonly found in farmers ’ fields of the Sahel hold potential as local and low cost resource for improving crop yield in millet and peanuts. G. senegalensis performs hydraulic lift which moves water from the wet subsoil to the dry surface soil at night when photosynthesis stops. This hydraulically lifted water could support microorganism even in the dry season and may assist crops through drought periods. Crop yields are higher in the presence of shrubs, but the mechanism for this response is not well understood. We hypothesized that shrubs may harbor a diverse community of Plant Growth Promoting Rhizobacteria (PGPRs). Therefore, the objective was to measure the growth response of millet in presence and absence of inoculating with putative PGPR from the genus Bacillus in a one-month greenhouse experiment in Dakar, Senegal. Using amplified ribosomal DNA restriction analysis (ARDRA), 11 different groups were identified in rhizosphere soil taken from G. senegalensis in farmers ’ fields. The millet plants were inoculated with individuals from each group, and the plants ’ growth measured. Using pair-wise comparisons between the control groups, water and bacterial medium, it was found that one of the Bacillus groups significantly (P < 0.1) increased the growth of millet plants