Rapid growth of Moso bamboo (Phyllostachys edulis) shoots (offspring ramet) is primarily fuelled by nitrogen (N) derived from parent ramet and absorbed by rhizome roots. However, the extent to which each N source supports the growth of offspring ramet and the underlying molecular mechanisms of N transport remain unclear. Here, clonal fragments consisting of a parent ramet, an offspring ramet, and an interconnected rhizome were established in a Moso bamboo forest. Additionally, 15N isotope tracing and transcriptome profiling were conducted concurrently to quantify the N contribution from the parent ramet and rhizome roots to the offspring ramet, and to reveal the molecular mechanisms underlying N transport during rapid growth (i.e. early, peak, branching, and leafing stages). The N acquisition strategy of offspring ramet shifted from being primarily provided by the parent ramet (72.53%) during early stage to being predominantly absorbed by rhizome roots (69.85%) during the leafing stage. Approximately equal N contributions (45.82%–54.18%) from the parent ramet and rhizome roots were observed during peak and branching stages. PeAAP29123 was identified as a key gene for N transport, being most closely correlated with 15N content. Biomolecular assays demonstrated that PeHDZ23987 could activate the expression of PeAAP29123 via two types of HD-motifs. Overexpression of PeHDZ23987 and PeAAP29123 significantly enhanced N starvation tolerance in transgenic rice with significantly improved N uptake efficiency. Our findings clarify the pattern and mechanisms of N supply for the rapid growth of Moso bamboo offspring ramet and provide transcriptomic evidence for long-distance N transport between clonal ramets.

Introduction: Accurate understanding of soil phosphorus (P) fractions is crucial for enhancing plant productivity and deciphering forest succession patterns; however, the dynamics of rhizosphere soil P fractions and their influencing factors during forest succession or land-type conversion, particularly in highly weathered tropical and subtropical regions, have not been comprehensively elucidated. Methods: Using a space-for-time replacement strategy, in this study, we examined how Moso bamboo ( Phyllostachys edulis ) expansion into Chinese fir ( Cunninghamia lanceolata ) forests affects P fractions in rhizosphere soil across various seasons within a subtropical region. The research focused on seasonal variations in soil P dynamics resulting from this invasive expansion. We further evaluated key drivers, encompassing soil physicochemical characteristics and microbial traits. Results and discussion: Compared to pure Chinese fir forests, mixed bamboo–fir stands had significant reductions in total P (excluding spring), CaCl ₂ -P, Citrate-P, Enzyme-P (excluding spring), and HCl-P (excluding winter) throughout the seasonal cycle ( p < 0.05). Pure bamboo forests showed further reduction in total P, Citrate-P, Enzyme-P, and HCl-P, along with reduced CaCl ₂ -P (except summer and winter) ( p < 0.05), with most P fractions (except CaCl ₂ -P in summer, Citrate-P and HCl-P in summer and autumn, and Enzyme-P in summer) being lower in these stands than in mixed forests, which showed a decreasing trend with increasing expansion intensity. CaCl ₂ -P, citrate-P, and HCl-P levels were consistently higher in summer and autumn than in winter and spring across Moso bamboo, Chinese fir, and mixed forest stands. Variations in P fractions were under the major control of nitrogen components and soil pH. This study highlights the importance of clarifying P fraction dynamics to understand forest succession mechanisms and informing P management strategies for enhancing forest productivity.