Tree species-specific strategies of soil aggregation driven by SOC-GRSP coupling under nitrogen addition and precipitation reduction.

Soil structural stability underpins ecosystem function, yet how nitrogen (N) enrichment and precipitation reduction jointly regulate glomalin-related soil proteins (GRSP) and aggregate formation in temperate forests remains poorly understood. This knowledge gap limits predictions of soil carbon persistence under global change. A factorial field experiment was conducted in an old-growth temperate forest with four treatments (CK, + N, -P, + N-P) across three dominant tree species. Rhizosphere soils were analyzed for total and easily extractable GRSP (T-GRSP, EE-GRSP), aggregate-size distribution, and physicochemical properties. Random forest modeling and structural equation modeling (SEM) were used to identify key regulatory pathways. N addition significantly increased EE-GRSP (3.92-5.74 mg g ⁻ ¹) and macroaggregates (4-8 mm: 21.6%-34.8%), while precipitation reduction reduced EE-GRSP (by 36.5%) and increased microaggregates (0.053-0.25 mm: + 29.3%). soil organic carbon (SOC) was strongly and positively correlated with EE-GRSP (R² = 0.69-0.63), T-GRSP (R² = 0.82-0.77), MWD (R² = 0.85-0.67), and GMD (R² = 0.84-0.72). Random forest identified EE-GRSP and SOC as dominant predictors of aggregate stability. SEM revealed that SOC regulated GRSP and MWD through NH₄ ⁺ -N and SWC (Fig. 2-5). Our findings highlight a coupled "carbon-protein-structure" pathway in regulating soil aggregation. The regulatory effects of N and water are both species-specific and pathway-integrated, emphasizing the role of SOC-mediated GRSP dynamics in sustaining soil physical integrity under climate perturbations.