Background and Aims <p>Age-related alterations in nitrogen (N) acquisition by canopy trees has been extensively explored; however, little is known regarding N uptake strategy of coexisting plant species during forest plantation development.</p> Methods <p>A field experiment was conducted to evaluate plant N uptake in subtropical <i>Cunninghamia lanceolata</i> plantations of varying ages (7, 15, 24, and 34&#xa0;years). Using a hydroponic method, we assessed the root capacity to uptake NH₄⁺, NO₃⁻, and glycine by the coexisting tree (<i>C. lanceolata</i>), a shrub (<i>Ficus hirta</i>), and a herb (<i>Pteris semipinnata</i>).</p> Results <p>Both the canopy and understory vegetation preferred NH₄⁺ as a N source in hydroponic culture, followed by glycine and then NO₃⁻. Root N uptake rates with increasing plantation age varied by plant species and N source. For <i>F. hirta</i>, the NO₃⁻ uptake rate increased from 0.38 to 0.78&#xa0;μg N·g⁻¹ root·h⁻¹, while it decreased from 1.64 to 0.30&#xa0;μg N·g⁻¹ root·h⁻¹ for <i>P. semipinnata</i> as the <i>C. lanceolata</i> plantation developed. No clear pattern was observed for <i>C. lanceolata</i>. A positive relationship between root AM colonization rate and NO₃⁻uptake rate was observed for <i>F. hirta</i>, but not for <i>C. lanceolata</i> and <i>P. semipinnata</i>. The contribution of glycine to <i>P. semipinnata</i> total N uptake increased progressively with plantation age.</p> Conclusion <p>Our results indicate that N acquisition among coexisting tree and understory vegetation varied with plant species and N form in hydroponic culture. Notably, understory plants exhibited greater flexibility in N acquisition than overstory trees during the development of subtropical <i>C. lanceolata</i> plantations.</p>