Deterministic abiotic filtering and halophilic core microbiomes shape bacterial communities in costal salt flats (Sabkha) of southern Morocco

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 consistently 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 ASVs shared across compartments. Host identity played a secondary role, as environmental filtering overshadawed host-specific associations. Culture-dependent isolation recovered 19 halophilic and halotolerant bacterial strains, mainly, Halomonas , Idiomarina , Marinobacter , Psychrobacter , Planomicrobium and Bac illus, tolerating up to 25% NaCl. 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 shalped 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.