Functionally distinct roots of Phyllostachys glauca employ divergent phosphorus acquisition strategies across contrasting growth stages

Introduction Clonal bamboo undergoes two distinct growth stages with contrasting growth rates: a fast-growing stage (FG) and a subsequent slow-growing stage (SG). FG is characterized by rapid culm elongation and tissue formation, whereas SG is characterized by cessation of height growth and progressive tissue maturation. Plants may therefore need to adjust belowground phosphorus (P)-acquisition strategies across these contrasting stages to meet different resource requirements for growth. However, whether such adjustments occur, and how they differ between functionally distinct root types (culm roots and rhizome roots) and across P supply levels, remains unclear. Methods We investigated Phyllostachys glauca McClure growing in a low-P karst habitat under three P supply levels: low P (LP), medium P (MP), and high P (HP). Root morphological traits, carboxylate release, and rhizosphere available P concentrations were compared between culm roots (CR) and rhizome roots (RR) during FG and SG under these P supply levels. Leaf nutrient status was also analyzed across P supply levels and growth stages. Principal component analysis (PCA) was further used to evaluate coordinated variation among P-acquisition traits. Results Root morphological traits differed significantly between growth stages and root types. In the LP treatment, the specific root length (SRL) of RR during FG was approximately 2.36 times that during SG ( P < 0.05). Across treatments, RR generally exhibited greater SRL and specific root area (SRA), whereas CR had higher root tissue density (RTD), indicating contrasting morphological strategies. Carboxylate release was greater during FG, with total release under LP reaching 12.0 ± 2.0 and 10.9 ± 1.4 μmol g −1 root DW in rhizome and CR, respectively. Increasing P supply reduced the release of some carboxylate components, whereas rhizosphere available P concentrations generally increased, suggesting nonuniform responses among different P-acquisition processes. Leaf N:P ratios further suggested differences in nutrient balance between growth stages. PCA showed more evident separation between FG and SG samples than among root types or P treatments. Conclusion P-acquisition traits in P. glauca varied between growth stages. Functional differentiation between culm and RR became more evident during FG, and different P-acquisition processes responded differently to P supply levels. This growth-stage-dependent plasticity provides new insights into the functional regulation of root nutrient foraging in clonal plants, and highlights the need to incorporate growth-stage variation in root function into predictions of plant responses to fluctuating nutrient availability.