Biodegradable microplastics impact on soil: how poly-3-hydroxybutyrate alters microbial diversity and nitrogen mineralization processes

Abstract

Background: Poly-3-hydroxybutyrate (P3HB) is a biodegradable plastic that may affect soil quality and plant growth. To explain the observed deterioration of plant growth, this study investigated the effects of P3HB microplastics on the soil microbiome and its activity related to content of nutrients and their transformation processes. A pot experiment was conducted using soil contaminated with five different doses of P3HB, both with and without maize. Soil mineral nitrogen forms, microbial properties as well as plant biomass were determined. Results: P3HB significantly altered soil properties by stimulating microbial respiration, enhancing carbon turnover, and shifting nitrogen forms, notably reducing NO₃⁻ availability. The fungal community was more sensitive to P3HB compared to the bacterial one. Fungal genera such as Tetracladium, Exophiala, and Pseudogymnoascus were stimulated; others such as Gibberella and Gibellulopsis declined. In the bacterial community, P3HB promoted the growth of copiotrophic P3HB degraders (e.g., Actinobacteria, Alphaproteobacteria); increased the abundance of anaerobes (Clostridia); decreased nitrifying groups (Nitrososphaeria, Nitrospiria); and reduced oligotrophic taxa (Vicinamibacteria, Thermoleophilia). These changes led to altered nutrient cycling, including inhibited nitrification and reduced mineral nitrogen availability, contributing to decreased maize growth. Conclusions: Soil contamination with ≥ 1% P3HB microplastics disrupts microbial structure and nutrient dynamics, with potential negative effects on soil fertility and plant productivity.Computational resources were provided by the e-INFRA CZ project (ID: 90254), supported by the Ministry of Education, Youth and Sports of the Czech Republic. The research was partially supported by European Union\u2019s Horizon 2020 Research and Innovation Program under Grant Agreement No. 862910 (SEALIVE), Horizon Europe project ARAGORN under grant agreement ID 101112723 and Ministry of Agriculture of the Czech Republic, institutional support MZE-RO1225. This work was also supported from OP JAC project (POCEK), number CZ.02.01.01/00/23_021/0009004.Ministry of Education, Youth and Sports of the Czech Republic [90254]; European Union [862910]; Horizon Europe project ARAGORN [101112723]; Ministry of Agriculture of the Czech Republic [MZE-RO1225]; OP JAC project (POCEK) [CZ.02.01.01/00/23_021/0009004