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Discrepant effects of microplastics on soil phosphorus availability under different phosphorus fertilizer applications
Summary
Researchers studied how polyethylene and polylactic acid microplastics interact with different types of phosphorus fertilizers in soil over 56 days. They found that microplastics reduced the amount of plant-available phosphorus in organically fertilized soils by up to 29%, while increasing it in soils treated with mineral fertilizer. The findings suggest that microplastic contamination in farmland could alter how effectively crops access essential nutrients depending on the fertilizer type used.
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.