Microbiome-guided rhizosphere engineering for sustainable remediation of agricultural soil contaminants

Agricultural soils increasingly carry mixtures of pesticide residues, heavy metals, petroleum hydrocarbons and microplastics, and conventional phytoremediation is too slow and too contaminant-specific to address them. Rhizosphere engineering, the deliberate manipulation of root-associated microbial communities, is widely proposed as the alternative, but the literature reports laboratory, pot and field results in a single register, so a reader cannot easily tell which approaches are deployable. This mini-review stratifies that evidence rather than surveying it. Every approach examined is assigned to one of three tiers: field-validated, emerging at pot or microcosm scale, or conceptual. Only two domains prove to be field-validated, namely metal immobilization and phytoextraction through bioaugmentation and bulk amendment, and hydrocarbon rhizoremediation by defined consortia; both rest on cultured isolates rather than engineered organisms. Microplastic rhizoremediation has not been demonstrated in soil, and we separate interception, adsorption, weathering, transformation and mineralization to show why reported removal is usually not degradation. Synthetic biology, CRISPR-based community editing and computational design remain conceptual, and we set out the horizontal gene transfer, containment, non-target and regulatory obstacles that stand between them and field use. We identify the measurements that would move an approach from one tier to the next, and argue that the principal deficit in this field is not technical capability but field-scale evidence reported to a common standard.