Microbial community shifts in pearl millet root zone soils with Guiera senegalensis intercropping along a rainfall and soil type gradient in the Sahel

The Sahel of West Africa has vulnerable agroecosystems that threatens food security. A potential solution is intercropping with the indigenous shrub, Guiera senegalensis J.F. Gmel. Previous research of the Optimized Shrub-intercropping System (OSS) (high density of similar to 1,500 shrubs ha(-1) and coppiced residue incorporation) has been shown to dramatically improve pearl millet [Pennisetum glaucum (L.) R. Br.] yield, which is attributed to improved soil quality, nutrient and water availability, and harboring a distinct microbial community. Whether this response is consistent over a climate and soil type gradient in farmers' fields has not been investigated. Therefore, the objective was to determine the impact of G. senegalenis on soil chemistry, enzyme activity, microbiomes, and metabolic pathways of millet root zone soils in farmers' fields. The experiment was a three-by-two factorial with three rainfall and soil type sites along a north-south gradient in the Senegal Peanut Basin and two sampling locations (millet root zone soil within and outside the influence of the G. senegalensis). Guiera senegalensis shifted certain predicted bacterial metabolic pathways and enriched some bacterial and fungal genera. Notably, the increased crop growth due to G. senegalensis positively correlated with the abundance of genera having plant growth promoting properties (e.g., Enterobacter agglomerans and Paraburkholderia). Paucibacter, a genera that has deleterious and/or pathogenic properties, was highly abundant in non-shrub soil but completely suppressed beneath the shrub. The results showed that G. senegalensis in farmers' fields even at typical, low densities, where coppiced residues are annually burned, still increased soil chemical and microbial properties, suggesting that a more important factor than litter is the presence of shrub roots that provide root turnover and exudates, and water inputs through hydraulic lift.