Geographical variation of Geochemistry and Bacteriome of Maize Rhizosphere in Agricultural Farmlands

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Abstract Sustainable food production systems in developing countries require resilient production of crops like Zea mays (maize) with understanding of its rhizosphere bacteriome. Maize rhizospheres in six locations, representing two main hemispheres (southern: Ma2R, Ma3R, and BaMR; northern: MF1A-R, MF2A-R, and MF3A-R), were assessed for geochemistry and 16S rRNA microbiome. The pH of the rhizospheres tends mostly towards acidic (6.33–6.98) with some significant variations (p < 0.05) in the geochemical features across the locations. Varied concentrations of organochlorine compounds were observed in the rhizospheres, where endrin was recorded in all the rhizospheres. The dominance of Proteobacteria, Actinobacteria, Firmicutes, Acidobacteria, Chloroflexi, Plactomycetes, Verrucomicrobia, and Bacteroidetes with apparent variations was observed across the locations. Firmicutes (as evidenced with Bacillus fumarioli group) varied significantly between MF2A-R and MaMR (t = 2.96; p < 0.05), Ma3R (t = 3.99; p < 0.01), and Ma2R (t = 3.13; p < 0.05). Remarkably, Proteobacteria (represented by Bradyrhizobium japonicum group) was relatively higher in the maize rhizosphere from the southern (Ma2R, 24.8%; Ma3R, 37.8%; BaMR, 37.6%) than in northern (MF1A-R, 22.1%; MF2A-R, 25.6%; MF3A-R, 27.1%) hemispheres. Contrariwise, the abundance of Acidobacteria (mostly unclassified species), Chloroflexi and Actinobacteria skewed towards maize rhizospheres in the northern sphere indicating oligotrophic ecosystem. The phylogenetic Diversity index revealed Ma2R was the most diverse phylotypes with a 5142-factor followed by MF1A-R (4957), Ma3R (4949), MF2A-R (4465), MF3A-R (4440), and the least diverse was BaMR (4284). Canonical correspondence analysis and other beta-diversity indexes established a 19.6% variance between the southern and northern rhizosphere as the bacteriome related to environmental fluxes through 64.4% variability.

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