Abstract: The observations of this study were to measure the contents of soil organic carbon (C), total nitrogen (N) and total phosphorus (P) in soil layer from 10 cm to 100 cm in depth under the planted Pinus sylvestris var. mongolica forests with different stand ages (for 15, 25, 35 and 45 years) over the Horqin Sandy Land. Moreover, the vertical distribution of ecological stoichiometric ratios of soil organic C, total N and total P under the planted forests with different stand ages was investigated so as to provide a theoretical basis for sustainable management of the planted forests. The results showed that the contents of soil organic C, total N and total P varied in ranges of 2.51-8.27, 0.12-0.45 and 0.14-0.21 g·kg^-1 respectively, and all of them were below the national average level in China. As the increase of stand age of the forests, the contents of soil organic C, C/N and C/P were increased; the total N and total P were increased at first and then decreased, a significant decrease occurred under the forest with a 45 year stand age, and there was no significant change in N/P. As the increase of soil depth, both the soil organic C and total N were decreased, their contents were lower than one third of the total. While the C/N was increased but the C/P was decreased. The study results revealed that the soil C, N and P storages were increased although the contents of these soil nutrients were extremely poor in the Horqin Sandy Land.

Key words: Pinus sylvestris var. mongolica, stand age, soil, ecological stoichiometry, Horqin Sandy Land