Soil microbial functional capacity and diversity in a millet-shrub intercropping system of semi-arid Senegal

• Native shrubs might be used as part of Sub-Saharan small-farming systems.
• The shrub altered both microbial DGGE-profiling and enzyme activities in millet soil.
• Shrub effects on bacteria and fungi are mediated by soil chemical parameters.

A few species of shrubs grow with dryland row crops in farmers’ fields throughout the Sahel and can significantly increase crop yield. The presence of shrub roots and litter inputs should have implications for soil nutrient pool sizes but there is limited information on the interactions of these shrubs with microbial communities involved in biogeochemical processes. Therefore, the objective of this study was to determine the microbial composition and functional capacity of soil from the rooting zone of pearl millet (Pennisetum glaucum) grown in the presence or absence of the shrub Piliostigma reticulatum in Senegal. Soil samples were collected from a long-term field study where millet was cultivated alone or intercropped with P. reticulatum with annual incorporation of coppiced shrub residues. Higher nutrient contents and distinct differences in microbial communities (DGGE profiles) were found between soils from beneath the canopy compared to soil outside the influence of shrubs. The catabolic response profile (MicroResp™) showed that the soil microbial community at both shrub and non-shrub sampling locations, metabolized a wide range of substrates. Trehalose that can work as a signaling molecule was more rapidly degraded in the rooting zone of millet growing in the presence of P. reticulatum over millet alone. Urease, arylsulfatase and dehydrogenase activities in the millet root zone soil were higher when intercropped with P. reticulatum which indicates enhanced potential of biogeochemical processes to proceed in the presence of this shrub. It is concluded that the native shrub P. reticulatum promotes a more diverse and active microbial community in the rooting zone of millet and further indicates greater potential to perform decomposition and mineralize nutrients.