Abstract: The aim of this study was to clarify the nutrient characteristics and stabilization mechanisms of Pinus sylvestris var. mongolica plantation. With Pinus sylvestris var.mongolicaplantations at sapling, young, mature and overmature stages in the Zhanggutai area of Northwestern Liaoning Province as the research objects, we examined the characteristics of C, N and P contents and ecological stoichiometry ratios in soil, needles, and  microbial biomass. We further analyzed the coupling relationship and homeostasis characteristics of those components. The results showed that C, N and P contents were poor in this area. Compared with the global mean value, needles were higher in C, P and lower in N. Compared with the  different stand ages, we found that soil C contents reached the peak value of 12.93 g·kg^-1 in overmature plantation; soil N and P contents peaked at 0.41, 0.25 g·kg^-1, needles C, N and P contents peaked at 641.38, 10.18, 1.81 g·kg^-1, microbial biomass C peaked at 165.68 mg·kg^-1, which all appeared in mature plantation. Microbial biomass N and P reached the peak value of 9.29, 2.92 mg·kg^-1 in young plantation. Soil C∶N of Pinus sylvestris var. mongolica plantation across different stand ages was much higher than the national average level of China, which showed N limitation. Only soil C∶P of overmature plantation was higher than the national average level of China, which showed P limitation. The soil, needles, and microbial biomass C∶N and C∶P of Pinus sylvestris var. mongolica of each stand age reached their peaks in overmature forests, and showed the strongest degree of N and P limitation. The stoichiometric characteristics of the three components (soil, needles, and microbes) had significant coupling relationships, and the relationship between microorganisms and soil was closer. In general, the homeostasis of nutrients and stoichiometric indicators in needles were much higher than that of microbes. It is recommended to apply N fertilizer reasonably in this area to improve the supply of soil nutrients, and to ensure the sustainability and stability of the ecosystem by introducing N fixing  plants. Meanwhile, more attention should be paid to the changes of soil microorganisms and timely supplement of organic fertilizer to improve soil quality during the management of Pinus sylvestris var. mongolica plantations.

Key words: Pinus sylvestris var.mongolica, ecological stoichiometry, homeostasis, microbial biomass, stand age, sandy land.