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.