Impacts of microplastics on rhizosphere microbiome structure and function: a systematic review

The pervasive contamination of agricultural soils by microplastics (MPs) represents a significant environmental stressor with potential repercussions for the rhizosphere microbiome, a critical interface for plant health and soil fertility. This systematic review synthesizes findings from 32 primary studies to evaluate MP-induced stress and its impacts on rhizosphere microbial communities. The evidence consistently demonstrates that microplastics significantly alter microbial community structure, with the majority of studies reporting substantial shifts in beta diversity. The effects on alpha diversity were context-dependent, varying with factors such as polymer type, concentration, and the presence of co-stressors; studies reported both significant decreases (a 9-10% reduction in bacterial richness with 100,000 mg kg^-1 polylactic acid (PLA) MPs) and increases. A critical finding was the marked reduction in beneficial microbial guilds; for instance, specific plant growth-promoting rhizobacteria (PGPR) genera declined significantly (p < 0.05) under combined MP and antibiotic stress. Furthermore, biodegradable microplastics (BMPs; e.g., PLA, poly(butylene adipate-co-terephthalate (PBAT)) induced equally potent or more severe disruptions than conventional polymers, often enriching copiotrophic bacteria and altering functional gene profiles for nutrient cycling. Under the high‑dose, short‑term experimental conditions reviewed, these perturbations compromise plant nutrient acquisition and stress resilience; however, whether such effects scale to environmentally realistic microplastic concentrations remains an open question, necessitating caution when extrapolating to long‑term agricultural sustainability. The review underscores the urgent need for field-relevant, long-term studies to fully understand the ecological risks posed by MPs in terrestrial ecosystems.