Root Class-Specific Phosphorus Dynamics and Antioxidant Defense Responses in Contrasting Chinese Fir Clones Under Phosphorus Deficiency

Abstract Aims Phosphorus (P) deficiency is a serious constraint on the productivity of forest plantations, especially in Chinese fir ( Cunninghamia lanceolata ). This study aims to determine how P availability affects root class-specific P acquisition, antioxidant responses, and physiological adaptations in two contrasting Chinese fir clones (020 and 061) across three harvesting periods. Methods Seedlings were grown in P-deficient (P 0 ) and P-replete (P 1 ) conditions, and P dynamics and antioxidant responses were determined across root orders, shoots, and needles. Results Generally, P concentration and accumulation increased with harvesting time and were significantly higher in P-replete conditions, with clone-061 being the better P acquirer than clone-020. P concentration and accumulation differed significantly among root classes, indicating functional specialization in P acquisition and distribution. P uptake and translocation were highest during early harvestings, while P use efficiency was higher at later growth stages. Under P deficiency, the activities of antioxidant enzymes, such as superoxide dismutase, peroxidase, and catalase, increased with harvesting time, especially in clone-061, and the malondialdehyde content decreased with harvesting time and remained comparatively lower in clone-061, indicating reduced oxidative damage. According to principal component analysis, both P acquisition and antioxidant enzyme activity were positively associated with antioxidant responses and negatively associated with malondialdehyde in a distinct, root-class-specific manner. Conclusions Overall, clone-061 exhibited superior P acquisition, utilization efficiency, and antioxidant capacity, highlighting its greater adaptation to phosphorus-limited environments. These findings reveal root-specific P-use strategies and support selecting P-efficient Chinese fir genotypes for sustainable plantation management.