Biodegradable Film Mulching Increases Soil Carbon Sequestration and Microbial Network Complexity in a Long-Term Field Study

The adoption of biodegradable plastics, such as poly (butylene adipate-co-terephthalate) (PBAT), in agriculture is promoted as a sustainable alternative to conventional polyethylene (PE) mulching. However, concerns persist regarding their incomplete degradation into microplastics (MPs) and their long-term impact on soil ecosystems. Based on a multi-year field experiment initiated in 1998 with a completely randomized design comparing three treatments: no mulching (NoMul), continuous PE mulching (PolyMul), and a transition from 15 years of PE to 11 years of biodegradable film (PBAT) mulching (BioMul). We evaluated the effects of mulch transition on soil carbon dynamics, microbial communities, and MPs accumulation.

Results show that soils under BioMul accumulated a higher load of MPs than those under PolyMul, with the presence of finer particles and unique polymer intermediates indicating ongoing degradation. Despite MPs accumulation, BioMul increased total soil organic carbon (SOC) and the mineral-associated organic carbon (MAOC) fraction throughout the soil profile (0–100 cm). In surface soil (0–30 cm), SOC under BioMul was 4.0–13.0% higher than under PolyMul or NoMul. This carbon accrual was accompanied by an increase in avtive carbon pools, with dissolved organic carbon (DOC) and microbial biomass carbon (MBC) showing higher concentrations under BioMul in 0–30 cm and 60–100 cm depths. Microbial alpha diversity was decreased, while community composition shifted toward a more functionally integrated structure, characterized by the enrichment of bacterial phyla such as Proteobacteria and Bacteroidetes, and increased fungal (Ascomycota) participation. Co-occurrence network analysis further revealed that BioMul formed a more connected and robust microbial network with stronger bacterial-fungal associations, indicating improved functional synergy within the soil microbiome.

Our findings demonstrate that long-term biodegradable film mulching can increase both stable carbon pools, while fostering a cooperative and functionally integrated microbial community, despite the accumulation of MPs. This study provides field evidence that PBAT mulch supports key aspects of soil ecological function and highlights the importance of management practices in realizing the environmental benefits of biodegradable plastics in agriculture.