Differential Phosphorus Allocation in Leaves and Roots of Yushania shuichengensis Across Soil Phosphorus Gradients: Implications for Ecological Adaptation and Resource Use Efficiency

Phosphorus (P) availability critically limits plant growth in ecosystems. Plants adapt by regulating internal P fractions, yet how these fractions underpin ecological strategies in wild plants remains unclear. We investigated the allocation of P fractions in Yushania shuichengensis along a natural soil total P (TP) gradient (Low-P: 0.66, Moderate-P: 1.60, High-P: 2.73 g kg−1) in the Yunnan-Guizhou Plateau. In leaves, concentrations of metabolic P (PM) and lipid P (PL) showed a unimodal response, peaking at the Moderate-P site (e.g., PM increased by approximately 45% compared to the Low-P site), whereas the High-P site favored the storage of inorganic P (Pi) and residual P (PR). In roots, Pi concentration increased linearly with soil TP, indicating a tight coupling with geochemical supply. Phosphorus resorption efficiency (PRE) decreased with increasing green leaf TP and PM concentration but was unrelated to the relative allocation of P fractions. Net photosynthetic rate was governed by the absolute concentrations of P fractions rather than their reallocation. Conversely, root morphological traits were positively correlated with nucleic acid P allocation (rPN), underscoring its role in promoting root elongation. Our findings reveal that Y. shuichengensis relies on regulating the concentrations of key P fractions in a context-dependent manner, rather than reallocating internal P, to adapt to soil P heterogeneity, with significant implications for its distribution and nutrient management.