Ecological stoichiometry in leaves, branches, and soils of <i>Pinus tabuliformis</i> at different stand ages in the Taihang Mountains, China.

To understand the changes and relationship of plant-soil eco-stoichiometric characteristics of <i>Pinus tabuliformis</i> plantations with stand ages, we investigated <i>P. tabuliformis</i> plantations of different stand ages (10, 23, 39, and 47 years old) in the Taihang Mountains. We measured the concentration and stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) in leaves, branches, and soils at different layers. We analyzed the relationship between leaf, branch nutrient characteristics and soil physicochemical properties. The results showed that soil C and N contents decreased after an initial increase with increasing stand ages, being the maximum at the 39 years old stand, while P content was the maximum at 47 years old stand. Soil C:P and N:P of the 23 years old stand were significantly higher than that of other stand ages, indicating that P was the limiting factor for <i>P. tabuliformis</i> growth. With increasing soil depth, the concentration of C, N, P, C:P and N:P in soils of different stand ages decreased, while the C:N increased, suggesting an enhanced N limitation. The stoichiometric characteristics of soils at different depths varied significantly among different stand ages, particularly in the upper soil layers (0-20 cm). The N content in leaves and branches increased first and then decreased, while the P content decreased first and then increased. The C:P and N:P in leaves and branches were higher at 23 years old, indicating a synergistic effect of nutrient acquisition between leaves and branches. Soil C concentration was significantly positively correlated with leaf N, while soil C:N was significantly positively correlated with branch C:N. There was a stronger correlation in the deeper soil layers (20-60 cm) than the upper soil layers. Soil sand content and N:P were key factors influencing nutrients in leaves, while soil P and C contents were the main factors influencing nutrients in branches. Soil water content (SWC), soil N content, and soil C:N jointly regulated nutrient variations in leaves and branches. Compared to the upper soil layers, the deeper soil layers showed a more pronounced N limitation. The impact of SWC on nutrient availability was relatively minor. Soil C:N (17.0) was higher than the national average, while the N:P in both leaves (8.2) and branches (8.3) were lower than 14, indicating increasing N limitation with increa-sing stand ages. To ensure the development of <i>P. tabuliformis</i> plantations and improve nutrient cycling, P and N fertilizers could be applied during the mid to late growth stages of <i>P. tabuliformis</i> plantations.