Diversity of Bacterial Communities in Soils of Moroccan Oases as Affected by Edaphic Factors

Soil microbial community structure and function are key to the sustainability of oasis ecosystems, which are fertile areas in deserts with water, supporting life and human settlements. In this study, we analyzed the composition and diversity of soil bacterial communities across three Moroccan oasis regions. Marrakech with Kastanozem, Errachidia with Calcisol, and Zagora with Calcisol using high-throughput 16S rRNA gene sequencing. The results revealed significant spatial variation in community structure, which was strongly influenced by edaphic variables such as pH, nitrate, and available phosphorus. PERMANOVA analysis confirmed that the site was a significant determinant of bacterial community composition (F = 26.75, R2 = 0.48, p = 0.000011). Alpha diversity was highest in Marrakech (Shannon: 4.12 ± 0.25; Simpson: 0.92 ± 0.01), followed by Errachidia and Zagora, indicating richer and more even bacterial communities in Marrakech. Proteobacteria (38–40%), Firmicutes (20–25%), and Bacteroidota (12–22%) were the dominant phyla, with Bacteroidota being particularly abundant in Zagora. Bacillaceae was the most dominant family (35–45%), and peaked in Marrakech. Beta diversity analysis (NMDS and PCoA) showed clear clustering of samples by site, especially for Marrakech, reflecting the ecological differentiation. Venn diagram analysis revealed that 30.9% of OTUs (712 out of 2305) and 38.4% of genera (43 out of 112) were shared across all regions, while Marrakech showed the highest number of unique OTUs (508) and genera (26). Network analysis revealed a modular OTU-level structure (100 nodes, 210 edges; modularity = 0.57) with dominant modules involving Actinomycetota and Bacillota, suggesting structured co-occurrence patterns across the oases. These findings highlight the strong influence of soil chemical properties on the structuring of bacterial communities in Moroccan oases and underline the potential of microbial indicators for sustainable soil management in arid agroecosystems.