Abstract
Petroleum hydrocarbon pollutants pose a significant threat to the ecological security of oilfields. In these contaminated habitats, Suaeda salsa is a dominant halophyte of the coastal wetlands and oilfields, which has shown potential in remediation of petroleum polluted saline soils. However, the role of plant-associated microbial communities in pollutant attenuation remains poorly understood, particularly regarding niche-specific responses within the root zone. In this study, bacterial community structures associated with the halophyte Suaeda salsa in China's Yellow River Delta were investigated across three ecological niches comprising the endophytic tissues, rhizosphere soils, and bulk soils. A total of 54 samples from 6 sites were collected and analyzed using high-throughput absolute quantification sequencing and physicochemical analyses. Results demonstrated that petroleum hydrocarbons were the primary environmental drivers shaping bacterial community structure across all niches. Comparisons among ecological niches indicated that the rhizosphere effect further promoted the selection and enrichment of specific bacterial taxa, especially the genus Sphingomonas. Contrasting ecological strategies between niches were clearly resolved by co-occurrence network analysis, which showed highly connected networks in rhizosphere communities and modular structures in endophytic ones. Functional predictions further indicated niche-specific metabolic specialization, with endophytic communities enhancing xenobiotic degradation pathways and rhizosphere communities upregulating motility-related functions. These findings reveal the niche-dependent assembly and functional specialization of root-zone microbiomes under petroleum stress, thereby advancing our understanding of plant-microbe adaptive strategies in contaminated ecosystems.