Leaf–Litter–Soil C:N:P Stoichiometry Varies with Stand Age in Three Subtropical Plantation Types

Stoichiometry provides an integrative framework for evaluating nutrient dynamics in plantation ecosystems. However, whether stand-age-related changes in leaf–litter–soil carbon (C), nitrogen (N), and phosphorus (P) stoichiometry are consistent among plantation types remains unclear. Using a space-for-time substitution approach, we quantified C, N, and P concentrations, mass-based stoichiometric ratios, and leaf N and P resorption efficiencies across five species-specific stand age classes in Eucalyptus robusta, Pinus massoniana, and Cunninghamia lanceolata plantations in subtropical China. Stand-age-related patterns differed markedly among the three plantation types. In E. robusta, leaf N and P concentrations and soil total P generally decreased with stand age, whereas leaf C:P and soil C:P and N:P increased, with no significant age-related changes in N or P resorption efficiency (NRE and PRE). In P. massoniana, leaf nutrient concentrations, stoichiometric ratios, and resorption efficiencies remained relatively stable, whereas litter C and N varied nonmonotonically and soil organic C (SOC) and soil C:N and C:P peaked in the mature stand. In C. lanceolata, increasing N resorption efficiency was accompanied by declining litter N and P concentrations and increasing leaf N:P, litter C:N, C:P, and N:P, and soil N:P. These findings reveal plantation-type-specific shifts in nutrient distribution and conservation during stand development.