Deterministic abiotic filtering and halophilic core microbiomes shape bacterial community assembly in coastal salt flats (sabkha) of southern Morocco

Abstract

ABSTRACT Coastal salt flats, locally known as sabkhas, are hypersaline, alkaline desert ecosystems that impose extreme abiotic stress on microbial and plant life. Despite their ecological significance, plant-associated microbiomes in these habitats remain poorly characterized. In this study, we investigated the bacterial communities of native halophytes across three sabkha sites in southern Morocco using an integrated culture-independent and culture-dependent framework. Soil physicochemical analyses revealed strong gradients in salinity and ionic composition, along with consistent alkaline pH across sites. These conditions strongly structured bacterial assemblage: alpha diversity declined progressively from bulk soil to rhizosphere soil, root, and shoot; and beta diversity showed clear compartmental separation driven by environmental factors. Canonical correspondence analysis identified electrical conductivity (EC), Na₂O, K₂O, and carbonate fractions as the main abiotic drivers. Across plant species, bacterial communities converged toward a stable halophilic core microbiome dominated by Halomonas , Kushneria, and Marinococcus , with 66% of amplicon sequencing variants (ASVs) shared across compartments. Host identity played a secondary role as environmental filtering overshadowed host-specific associations. Culture-dependent isolation recovered 19 halophilic and halotolerant bacterial strains, including representatives of Halomonas , Idiomarina , Marinobacter , Psychrobacter , Planomicrobium, and Bacillus . These isolates exhibited robust growth on saline Marine Agar medium, indicating strong salt tolerance consistent with their occurrence in hypersaline environments. The strong concordance between cultured isolates and metabarcoding profile confirms that dominant halophilic lineages are both ecologically robust and readily culturable. Together, these findings demonstrate that sabkha plant microbiomes are primarily shaped by deterministic abiotic filtering and harbor resilient, stress-adapted bacterial communities. Sabkhas thus represent promising reservoirs of halophilic microbes with potential applications in saline agriculture and improving crop resilience under extreme environmental conditions. IMPORTANCE Coastal salt flats (sabkhas) are among the most extreme terrestrial environments, characterized by high salinity, alkalinity, and limited water availability. As soil salinization expands worldwide, understanding how life persists in such habitats is increasingly important for sustainable agriculture. This study shows that sabkha ecosystems impose strong environmental filtering on plant-associated bacterial communities, leading to highly structured microbiomes across soil, root, and shoot compartments. Despite differences among sites and plant species, bacterial communities converged toward a shared halophilic core microbiome, dominated by salt-adapted genera that are resilient to extreme ionic stress. Importantly, many of these dominant bacteria were readily culturable, highlighting sabkhas as accessible reservoirs of stress-tolerant microbes. Our findings demonstrate that abiotic conditions outweigh plant identity in shaping microbiome assembly under extreme stress and reveal sabkha halophytes as valuable natural models for discovering microbes with potential applications in saline agriculture, soil restoration, and crop resilience in salt-affected environments.