Biobased biodegradable microplastics (Bio-MPs) can alter both the quantity and molecular composition of dissolved organic matter (DOM) in soil, which profoundly shapes the stability of soil organic matter (SOM). However, the microbial mechanisms underlying the Bio-MP-induced DOM turnover, particularly the role of fungi, remain largely unclear. Here, we tracked DOM molecular dynamics using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and characterized microbial communities using 16S rRNA gene and ITS amplicon sequencing during a 30-day soil incubation amended with polylactic acid (PLA-MPs, low biodegradability) and polyhydroxyalkanoate (PHA-MPs, high biodegradability). Our results showed that PLA-MPs exerted minimal impacts on DOM dynamics, whereas PHA-MPs rapidly increased DOM content and CO2 emission and shifted the DOM molecular composition from recalcitrant compounds (e.g., lignins and tannins) toward labile compounds (e.g., lipids and proteins/amino sugars). These alterations were primarily driven by fungal depolymerization of PHA-MPs and SOM to generate labile DOM, followed by bacterial assimilation, indicating a fungal-initiated metabolic cascade that governs soil DOM turnover under PHA-MP exposure. The increase in labile DOM was mainly associated with enrichment of fast-growing fungi (e.g., Neocosmospora). Overall, this study elucidates the pivotal role of fungi in mediating Bio-MP-induced DOM turnover and shaping SOM stability.
Ma et al. (Wed,) studied this question.