The Diversity of Plastisphere Bacterial and Fungal Communities Differs between Biodegradable Polymer Types in Soil

Biodegradable polymers (BPs) are often seen as sustainable alternatives to conventional plastics. However, their actual degradability in soils, a major sink for plastic pollution, varies considerably. Moreover, their breakdown can influence soil microbial communities, with potential consequences for ecosystem function. Here, we compared the impacts of four major BP types: (1) poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), (2) poly(butylene adipate-co-terephthalate) (PBAT), (3) poly(butylene succinate) (PBS), and (4) poly(lactic acid) (PLA), on soil and plastisphere microbial communities. Standardised BP samples were buried in soil for 117 days, after which bacterial and fungal biomass load and diversity were assessed in the BPs and surrounding soils using quantitative PCR and metabarcoding. X-ray micro-computed tomography (µXCT) and gel permeation chromatography (GPC) were also used to compare signs of degradation. PLA exhibited negligible signs of degradation, no evidence of microbial colonisation, and minimal impacts on microbial diversity relative to bulk soil. In contrast, PHBV, PBAT, and PBS underwent marked degradation and supported distinct microbial assemblages with elevated biomass but reduced diversity, indicating selective enrichment of specific taxa. These findings demonstrate that BPs differ markedly in their environmental degradability and influence on soil microbial communities, providing insights to support polymer selection for more sustainable plastic use.