Plant–Microbe Interactions Driving Restoration of Petroleum-Contaminated Agricultural Soils in the Niger Delta: Hydrocarbon Removal, Soil Quality Improvement, and Rhizosphere Microbiome Dynamics

Petroleum contamination remains a major environmental challenge affecting soil fertility, ecosystem stability, and agricultural productivity in the Niger Delta region of Nigeria. This study examined plant–microbe interactions driving the restoration of petroleum-contaminated soils, focusing on hydrocarbon degradation, soil physicochemical improvement, microbial community dynamics, enzymatic activities, plant growth performance, and functional gene expression. A greenhouse-based phytoremediation experiment was conducted using contaminated soils planted with selected species, while unplanted soils served as controls. Standard APHA methods were used for soil analysis, microbial populations were quantified using serial dilution and CFU enumeration, and rhizosphere bacteria were identified through morphological, biochemical, and 16S rRNA sequencing techniques. Molecular screening targeted hydrocarbon degradation genes including alkB, catechol 2,3-dioxygenase, and nahA. Results showed a significant reduction in total petroleum hydrocarbons (up to 78%) in planted soils compared to 22% in unplanted controls. Soil pH shifted from acidic (5.1) toward near-neutral conditions (6.5), while nitrogen, phosphorus, and organic carbon levels improved markedly in treated soils. Microbial load increased significantly in the rhizosphere (up to 9.5 × 10⁶ CFU/g), accompanied by higher diversity indices (Shannon index 3.4). Enzyme activities (dehydrogenase, urease, catalase) were substantially enhanced, indicating improved soil metabolic function. Plant growth parameters such as germination rate, shoot length, root length, and biomass showed strong recovery in treated soils. Gene expression analysis confirmed elevated abundance of hydrocarbon-degrading genes, while correlation analysis revealed strong positive relationships between microbial biomass, plant growth, and hydrocarbon degradation. The study concludes that plant–microbe synergy offers a highly effective and sustainable approach for restoring petroleum-contaminated agricultural soils and improving ecosystem functionality in the Niger Delta.