Differentiation and trade-offs of root phosphorus acquisition strategies in different phosphorus efficiency genotypes of Chinese fir

Chinese fir (Cunninghamia lanceolata), a vital afforestation species in southern China, exhibits genotypic variations in phosphorus (P) acquisition to adapt long—term soil P deficiency environment. This study aimed to elucidate how P-efficiency genotypes balance root morphology, rhizosphere exudation, and arbuscular mycorrhizal fungi (AMF) symbiosis to optimize P acquisition under varying soil P availability. Fourteen genotypes with contrasting P-use efficiencies (PUE) were subjected to low-P (5 mg/kg) and high-P (30 mg/kg) treatments, with or without AMF inoculation. Root morphological traits, exudates, AMF colonization, and carbon-phosphorus allocation were analyzed. Under low-P, high-P-efficiency (H-PUE) genotypes increased root length and surface area, reduced root diameter, and enhanced organic acid secretion and acid phosphatase activity. AMF inoculation under low-P suppressed root proliferation in H-PUE, while decreased acid phosphatase activity and dissolved organic carbon content, but increased organic acid concentration and AMF dependency. In contrast, low-P-efficiency (L-PUE) genotypes exhibited a degree of reliance on compensatory root biomass allocation and nonspecific dissolved organic carbon exudation. Principal component analysis revealed H-PUE genotypes synergized structural-symbiotic traits (e.g., fine roots, AMF colonization), whereas L-PUE genotypes relied on rhizosphere activation through acid phosphatase secretion. Functional differentiation in root P-acquisition strategies among Chinese fir genotypes is driven by carbon-phosphorus allocation trade-offs, where H-PUE genotypes optimize P uptake through integrated root morphological plasticity, targeted exudation, and AMF symbiosis, thereby minimizing carbon expenditure. This study elucidates the hierarchical coordination of root morphology, mycorrhizal collaboration, and exudate-mediated rhizosphere remodeling in woody plants, and provides mechanistic criteria for breeding P-efficient varieties and managing phosphorus-limited plantations.