Impact of Microplastics on Black Soil Aggregate Stability: A Novel Perspective from Glomalin-Related Soil Protein

Glomalin-related soil protein (GRSP), a glycoprotein secreted by arbuscular mycorrhizal fungi, is a pivotal agent in maintaining soil aggregate structure. Through a 30 month laboratory incubation experiment, this study examined how polyethylene microplastics (MPs) affect the stability of black soil in northeastern China from the perspective of GRSP alterations. The findings reveal that MPs significantly increased the concentrations of both total GRSP (T-GRSP) and easily extractable GRSP (EE-GRSP) within soil aggregates. This enhancement in GRSP levels enhanced the binding of soil particles, driving the coalescence of 0.25−0.5 mm aggregates into larger macroaggregates (>1 mm). Consequently, soil aggregate stability was markedly enhanced, as evidenced by significant increases of 6.22% and 6.29% in the mean weight diameter and geometric mean diameter, respectively. Furthermore, MPs substantially elevated soil organic carbon (SOC) levels across all aggregate fractions, with the most pronounced enhancement occurring in the smallest particles (<0.25 mm). Partial least squares path modeling (PLS-PM) indicated that T-GRSP, EE-GRSP, difficulty extractable GRSP (DE-GRSP), and SOC all positively contributed to aggregate stability, with EE-GRSP exhibiting the most substantial influence. In summary, these results demonstrate that MPs can enhance the structural integrity of soil aggregates and carbon storage potential by stimulating GRSP accumulation within aggregates.