Abstract: Increasing nitrogen (N) deposition exacerbates phosphorus (P) limitations in subtropical Chinese fir plantations, yet clonal mechanisms mediating root adaptation to heterogeneous P environments remain unclear. This study investigates the growth and metabolic responses of three clones (Y061/Y020: P-efficient; Y2C: P-sensitive) under N deposition and contrasting P distributions. Elevated N deposition enhanced aboveground and belowground biomass under heterogeneous P conditions, particularly enhancing Y061’s root length and surface area. Elevated N deposition significantly increased APase activity while decreasing organic acid secretion, particularly under homogeneous P-deficient conditions. Heterogeneous P supply amplified clonal divergence: P-efficient clones exhibited higher phosphorus absorption efficiency (PAE) than Y2C through root morphological plasticity, while N deposition upregulated APase activity but reduced total organic acids secretion. Metabolomic revealed N-driven shifts in exudate profiles, with lactic, malonic, succinic, and oxalic acid increasing while shikimic, quinic and malic acids decreased. Notably, nitrogen absorption efficiency (NAE) synergistically enhanced PAE under high N conditions. Clones Y061 and Y020 demonstrated superior N and P absorption capabilities, while clone Y2C prioritized enzymatic P mobilization in homogeneous deficiency but showed compromised growth. We demonstrate that N deposition restructures root foraging strategies along a “morphological-enzymatic” axis, where P-efficient clones exploit spatial nutrient heterogeneity through root proliferation rather than organic acid investment. These findings provide actionable solutions: (1) Deploying Y061 and Y020 clones in high-N regions improves productivity; (2) Mixed plantations mimicking heterogeneous P distribution enhance nutrient resilience. Our findings contribute to a deeper understanding of nutrient dynamics and providing targeted strategies for sustainable forestry in acidified subtropical soils.

Key words: APase activity, nutrient interactions, phosphorus efficiency, nitrogen deposition, root dynamics, root organic acids