Plant–Microbiome Interactions for Environmental Resilience: Rhizosphere Ecology, Climate Adaptation and Ecosystem Sustainability

Plant roots release a chemically diverse mixture of primary and specialised metabolites into the surrounding soil, and this exudation is now widely invoked as the principal means by which plants select, structure and exploit their rhizosphere microbiota. The proposition that exudates function as ecological signals, rather than as nutrient leakage that microorganisms passively consume, carries substantial theoretical and applied weight, yet the evidence for it is uneven. This critical narrative review evaluates what is known about the metabolic control of rhizosphere microbiome assembly and its consequences for plant adaptation to biotic and abiotic stress. Literature published between January 2000 and 27 July 2026 was identified through structured searches of multidisciplinary and life-science bibliographic sources, supplemented by citation tracking, and was appraised for design, causal inference, ecological realism and consistency. The synthesis distinguishes four explanatory layers: a broad substrate-driven filter imposed by sugars, organic acids and amino acids; selective gatekeeping by specialised metabolites such as coumarins, benzoxazinoids, triterpenes, flavonoids and saponins; reciprocal modulation of exudation by the microbiota itself; and stress-responsive shifts in exudation that recruit microorganisms associated with improved host performance. Genetic evidence from biosynthetic and transporter mutants now establishes that individual metabolite classes can reshape community composition, and several studies link these shifts to host iron nutrition, nitrogen acquisition, pathogen suppression or drought recovery. Confidence remains limited by the predominance of gnotobiotic and hydroponic systems, the difficulty of sampling exudates in soil without artefact, the small spatial reach of many compounds, strong effects of soil type that frequently outweigh host chemistry, and scarce field validation. The term signal is often applied without evidence that the response is adaptive for both partners. The review argues that exudate-mediated assembly is best treated as conditional niche construction whose outcomes depend on soil context, microbial tolerance traits and developmental timing. Priorities include spatially resolved exudate measurement in soil, multi-site field trials with defined genetic variants, and explicit tests of fitness consequences across plant generations.