Abstract: The distribution characteristics of soil nutrients in Picea schrenkiana forest were analyzed, and the comprehensive index of soil fertility (IFI) was calculated through principal component analysis to evaluate soil fertility levels under different altitudes, stand ages, and canopy densities, with the aim to provide a theoretical basis for scientific management of soil resources in Picea schrenkiana  forest. The results showed that: (1) soil carbon and nitrogen contents in 0-20 and 20-60 cm soil layers in Picea schrenkiana forest under different altitudes were 1900-2100 m > 2500-2700 m > 1700-1900 m > 2300-2500 m > 2100-2300 m. Soil carbon and nitrogen contents of 0-20 cm at the 1900-2100 m were significantly higher than those of 2100-2300 m (P<0.05). The IFI under this altitude was the highest (0.45), of which 63% of sampling plots reached grade I (high) and grade II (relatively high) in soil fertility, indicating that soil fertility was generally good in the range of 1900-2100 m. (2) Soil carbon and nitrogen contents showed an increasing trend with increasing stand age, with significant difference (0-20 cm soil layer) among mature forest, young forest, and middle-aged forest (P<0.05). The IFI of mature forest was 0.41, of which 54% of sampling plots reached grade I (high) and grade II (relatively high) in soil fertility. (3) Under the condition of high canopy density (>0.6), soil carbon and nitrogen contents in 0-20 cm soil layer was significantly higher than those under the condition of low canopy density (P<0.05), the IFI under high canopy density was higher (0.37), and 38% of sampling plots reached grade I (high) and grade II (relatively high) in soil fertility, but there was no significant difference. Taken together, the carbon and nitrogen contents in the surface soil of Picea schrenkiana forest were significantly affected by altitude, stand age, and canopy density, while the IFI was significantly affected by altitude and stand age.

Key words: Picea schrenkiana forest, soil nutrient, altitude, stand age, canopy density, soil fertility.