The Ecological Trap: Biodegradable Mulch Film Residue Undermines Soil Fungal Network Stability.

Biodegradable mulching films are promoted as alternatives to traditional polyethylene films, but their environmental impacts remain controversial. This study investigates how biodegradable films affect microplastic pollution of soil, fungal community structure, and ecological network stability. We conducted a maize field experiment comparing conventional polyethylene (CF, PE) and biodegradable (BF, PLA + PBAT) film residues. We used scanning electron microscopy and high-throughput sequencing of fungal ITS genes. We assessed soil properties, microplastic release, fungal communities, and network stability through co-occurrence analysis. BF degraded rapidly, releasing microplastic concentrations much higher than CF. BF increased soil carbon and nitrogen and substantially enhanced maize biomass. However, it significantly reduced soil pH and decreased key functional fungi (saprotrophs and symbionts) abundance. The fungal ecological network complexity and stability declined significantly. Correlation analysis revealed positive associations between saprotrophic and symbiotic fungi abundance and network stability. In contrast, CF reduced some nutrient levels but improved fungal network complexity and stability. This study reveals that biodegradable films create an "ecological trap." Short-term nutrient benefits mask systematic damage to soil microbial network stability. Our findings challenge the notion that "biodegradable equals environmentally friendly." Environmental assessments of agricultural materials must extend beyond degradability to include microplastic release, functional microbial responses, and ecological network stability.