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The impact of biodegradable microplastics on soil aggregate stability across different afforestation ages and soil depths in poplar shelterbelts
Summary
A field study in poplar shelterbelts found that biodegradable PLA and PBAT microplastics from agricultural films reduced soil aggregate stability, with effects varying by afforestation age and soil depth, suggesting biodegradable plastics still pose risks to soil structure in forestry systems.
Soil aggregates play a critical role in maintaining the ecological stability of forest ecosystems. Due to the widespread application of biodegradable plastics in farmland, the soil of shelterbelts planted on abandoned farmland may become a site for the accumulation of biodegradable microplastics (BMPs). BMPs may present ecological risks to shelterbelt ecosystems by influencing the stability of soil aggregates across various afforestation ages and soil depths. However, this potential impact remains insufficiently investigated. Herein, a 60-day incubation experiment was conducted to investigate the effects of BMPs (polyhydroxyalkanoates (PHA) and polylactic acid (PLA)) on aggregate size distribution, aggregate-associated carbon, and aggregate stability across various afforestation ages (0, 5, 10, 15, and 20 years) and soil depths (0-20, 20-40, 40-60, 60-80, and 80-100 cm). The results indicated that PHA led to a decrease in the microaggregate content (4.94-22.22%), while increasing the macroaggregate content (43.64-1167.04%) and the geometric mean diameter (GMD) of soil aggregates (7.39-49.05%) across all soil samples. Generally, PLA reduced the content of microaggregates (1.95-7.61%) while increasing that of macroaggregates (28.47-216.75%) and the GMD (10.23-29.07%) in the soils of 0-year-old shelterbelts. Furthermore, the extent of improvement in GMD (ΔGMD) and structural stability index (SSI) (ΔSSI) induced by PHA exhibited a positive correlation with increasing soil depth (P < 0.05). Since neither PHA nor PLA reduced the stability of soil aggregates across all afforestation ages and soil depths, the BMPs pose no ecological risk to shelterbelts based on soil aggregates in the short term.