Discrepant effects of microplastics on soil phosphorus availability under different phosphorus fertilizer applications.

The microplastic (MP) interaction with phosphorus (P) fertilizers and effects on P transformation and availability remain unclear. We conducted a 56-day soil incubation experiment with 1 % polyethylene (PE) and polylactic acid (PLA) microplastics (MPs) to analyze their influence on soil P fractions and availability under different P fertilizer regimes. While PE and PLA MPs had a negligible impact on P fraction and availability in unfertilized soils, they exhibited different effects in soils with organic fertilizer and calcium-magnesium-phosphate (CMP) fertilizer. Specifically, MPs decreased the available P content (13.95 %-28.99 %) in organic-fertilized soils after 28 days of incubation. This decreased available P was associated with reduced soil labile organic P content and soil acid phosphatase (ACP) activities. 16S rRNA high-throughput sequencing revealed that MP addition significantly reduced the relative abundance of Burkholderia-Caballeronia-Paraburkholderia (P < 0.05), potentially suppressing P mineralization and consequently decreasing soil P availability. In contrast to organic fertilizer-applied soils, available P content increased (4.48 %-26.95 %) in MP-treated soils with CMP fertilizer, leading to re-fixation of inorganic P by aluminum/iron (hydr)oxides. Arthrobacter and Streptacidiphilus might enhance P solubilization and mineralization in CMP fertilizer-applied soils after MP exposure. Traditional PE MPs exhibited a stronger influence on soil P availability than biodegradable PLA MPs, owing to their more pronounced effects on soil ACP activity and P-transforming microorganisms. These findings provided insights into the ecological risks of MP pollution in terrestrial ecosystems and emphasized the need to optimize P fertilizer application in the context of MP pollution and P resource limitation.