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Effect of Agricultural Beneficial Microbes on the Degradability of Polylactic Acid Film in the Farmland Environment
Summary
Exposure of polylactic acid (PLA) biodegradable films to three common agricultural microbes—Trichoderma harzianum, Bacillus cereus, and Pseudomonas fluorescens—accelerated PLA degradation, with one condition exceeding 30% mass loss over 360 days, driven by microbially induced shifts in soil community composition that enriched plastic-degrading Betaproteobacteria. These findings are significant for microplastic research because understanding PLA degradation rates and microbial drivers helps predict whether biodegradable agricultural films will fully break down or persist as microplastic-like fragments in soil.
Three common agricultural beneficial microbes, Trichoderma harzianum, Bacillus cereus, and Pseudomonas fluorescens, are widely used in the growth cycle of crops, and increase the yield of agricultural products through disease prevention and sterilization. As a biodegradable biological macromolecular material, polylactic acid (PLA) is also widely used in agricultural production as a biodegradable film. The addition of agricultural microbes will affect the degradation rate of polylactic acid and thus its agricultural use. Under specific conditions (Tri15), the degradation rate of PLA film exceeds 30%. Scanning electron microscopy (SEM) images show that the degradation of the PLA happened after 360 days of exposure to these three specific microbe environments, which makes the surface of PLA films crack. Gel permeation chromatography (GPC) analysis reveals that in the presence of these microbes, the molecular weight of PLA is reduced. The analysis of 16S rDNA sequences demonstrates that the introduction of these microbes alters the soil microbial community, resulting in an enhanced abundance of Betaproteomicrobes, promoting the degradation of PLA. These results indicate that the three microbes species significantly promote the degradation of PLA, and the effects of microbes vary for the different concentrations. This study establishes practical guidelines for the deployment of PLA in real-world farmland environments.