Biodegradable microplastics in soil-plant systems: bibliometric analysis and structured evidence synthesis of carbon cycling, rhizosphere microbiomes and plant responses

Biodegradable microplastics (Bio-MPs) are increasingly used in agriculture, yet their effects in soil-plant systems remain strongly context dependent. We combined Web of Science bibliometric analysis with structured evidence synthesis covering 2010 to 9 June 2026. Of 1,513 records retrieved, 1,392 were retained for bibliometric analysis after 121 documented exclusions. All 1,392 bibliometric records were further screened using predefined eligibility criteria, yielding 121 records for detailed evidence assessment and 105 unique original experimental studies for structured evidence synthesis. PLA and PBAT occurred in 69 (65.7%) and 30 (28.6%) studies, respectively, whereas only six studies (5.7%) used field settings. Research expanded rapidly after 2020 and increasingly addressed rhizosphere processes, microbial communities, carbon cycling and greenhouse-gas emissions. Across experimental studies, Bio-MP effects varied with polymer identity, dose, aging state, soil properties and plant-rhizosphere conditions. Soil carbon responses reflected competing processes involving polymer-derived carbon release, microbial assimilation, stimulation of native soil organic matter turnover, respiratory losses and carbon stabilization, rather than a consistent increase or decrease in soil carbon. Plant responses commonly involved altered nutrient acquisition, oxidative balance, photosynthesis and root development; among studies with extractable response directions, negative or decreasing plant/root effects occurred in 17 of 31 studies. Microbiome responses were predominantly mixed or context dependent (36 of 49 studies), and taxonomic shifts were reported much more frequently than direct functional validation. The evidence base therefore supports viewing Bio-MPs as both carbon inputs and ecological stressors whose consequences depend on environmental context, rather than as uniformly benign substitutes for conventional plastics. Major uncertainties remain because field-scale, time-resolved, carbon-fate and functionally validated microbiome studies are still limited.