Abstract: Aims Clarify the variation patterns and corresponding response mechanisms of plant functional traits and carbon-nitrogen stoichiometry in artificial plantations of different tree species under the age gradient. Methods In this study, Populus tomentosa, Platycladus orientalis and Styphnolobium japonicum at different ages were selected as the research objects to determine and explore the changes and relationships of different organ functional traits, carbon-nitrogen stoichiometry and soil physicochemical properties. Important findings (1) With the increase of forest age, the content of soil nutrients, clay and silt of different tree plantations increased significantly (P < 0.05). While soil total phosphorus content of P. tomentosa plantations, and soil pH value of P. orientalis plantations decreased. (2) The specific leaf area of different plantations increased significantly with the increase of forest age (P < 0.05), while the specific leaf weight decreased significantly (P < 0.05). The root carbon content (average 36.25 %) was lower than that of branches (45.52 %) and leaves (44.83 %), and the leaf nitrogen content (1.98 %) was higher than that of roots (1.30 %) and branches (0.64 %). With the increase of forest age, the nutrient content and carbon-nitrogen ratio of different organs varied with tree species. (3) The functional traits of P. tomentosa plantations of different organs were synergetic and consistent, while the functional traits of leaves and roots of P. orientalis plantations evolved independently, forming a strategic decoupling. (4) The increase of soil water content and the improvement of soil texture are important reasons for the changes in plant traits. (5) The soil total nitrogen content was significantly negatively correlated with the carbon content in leaves and roots (P < 0.05). RDA analysis showed that soil electrical conductivity was the significant factor affecting plant functional traits (P < 0.05). (6) Random forest analysis showed that the significant factors affecting the carbon-nitrogen ratio of leaves, branches and roots included soil total phosphorus and clay content, specific leaf area, leaf dry matter mass and plant nutrient content (P < 0.05). The results provide new insights for the theoretical system of plant economic spectrum, and have practical guiding significance for the sustainable development of ecological benefits of plantation.

Key words: Forest age, Functional traits, Plant economic spectrum, Carbon to nitrogen ratio