Abstract: In this paper, taking the natural broadleaved Korean pine mixed forest in Changbai Mt. as research object, 5 soil fractions of sand and stable aggregates (SA), acid insoluble fraction (AI), easily oxidized fraction (EO), particulate fraction (P) and soluble soil fraction (S) with different physic-chemical stabilities were separated by a physicchemical method. Weight percentages, organic C and N concentrations, C/N and allocation proportions of organic C and N in the various fractions were analyzed to explore the mechanism of potential of soil C sequestration and N supply. The results showed that the C/N of stable soil fractions (AI and SA) was 2-8 times higher than that in labile fractions (P and EO), which resulted in the different physic-chemical stability characteristics of soil fractions to soil microbial decomposition. About 90% of the soil quantity occluded on stable fractions (SA and AI), which leaded to the higher organic C in the AI (42.7%) and SA (29.5%) fractions. The organic C concentrations in labile soil fractions (P and EO) were 2-6 times higher than those in stable soil fractions (AI and SA), whereas in term of N, this difference was enlarged to 4-37 times. N was distributed similarly in labile fractions (EO,33.6% and P,19.7%) and stable fractions (AI, 21.1% and SA,24.3%). The results reveal the characteristic of the carbon sequestration is mainly intercepted on the stable components, while N is allocated fairly in the labile fractions and stable fractions in the broad-leaved Korean pine mixed forests in Changbai Mt. area. The characteristic of soil fractions is good for the long-term accumulation of soil carbon, and sustainable and fast supply of soil fertility of N.

Key words: carbon fractions, nitrogen fractions, carbon nitrogen ratio, allocation proportion