Discrepant soil microbial community and C cycling function responses to conventional and biodegradable microplastics

Area of Science:

• Environmental Science
• Microbiology
• Soil Science
• Polymer Science

Background:

• Biodegradable microplastics (MPs) are emerging as alternatives to conventional plastics, raising global concerns.
• The impact of biodegradable MPs on soil microorganisms and ecosystem functions remains poorly understood.
• Discrepant effects of different MP types and sizes on soil health necessitate detailed investigation.

Purpose of the Study:

• To investigate the differential effects of polyethylene (PE) and polylactic acid (PLA) MPs on soil microbiome and carbon (C)-cycling genes.
• To analyze the morphological and functional group changes of MPs under soil conditions.
• To identify the driving factors influencing MP effects on soil ecosystems.

Main Methods:

• High-throughput sequencing was used to analyze soil microbiome composition.
• Real-time quantitative PCR quantified C-cycling genes.
• Scanning electron microscopy and Fourier transform infrared spectroscopy examined MP morphology and functional groups.

Main Results:

• Distinct microbial taxa involved in MP degradation and nitrogen cycling were enriched with PLA and PE, respectively.
• PLA, smaller particle sizes (150-180 µm), and higher concentrations (5% w/w) enhanced soil network complexity compared to PE.
• Enzyme activities (β-glucosidase, amylase) and specific C-cycling genes showed varied responses to PLA and PE, influenced by size and concentration.

Conclusions:

• Biodegradable MPs, particularly PLA, exert distinct influences on soil microbial communities and C-cycling functions.
• Soil pH, nitrate-nitrogen levels, and MP biodegradability were identified as key factors mediating these effects.
• Findings provide a systematic understanding of biodegradable MP impacts on soil ecosystems and their potential implications for global climate change.