| In order to analyze the potential of soil carbon sequestration and fertility supply in different forests in NE China, the broad-leaved Korean pine forests and secondary poplar-birch forests in Changbai Mts.were selected as research objects, and5kinds of soil fractions (with different physic-chemical stability) of sand and stable aggregates soil fraction (SA), acid insoluble soil fraction (AI), easily-oxidized soil fraction (EO), particle soil fraction (P) and soluble soil fraction (S) were separated by a physical and chemical method with further determination of mass fraction, contents of C and N and their allocation proportions, C/N ratios, infra-red functional groups and X-ray diffraction (XRD) mineral crystallinity of these soil fractions. The main research conclusions were as follows.(1) The carbon contents in the stable soil fractions of AI (21.08mg·g-1/24.61mg·g-1) and SA (38.04mg·g-1/58.04mg·g-1) were lower than these of liable fractions of P (202.99mg·g-1/231.08mg·g-’),EO (39.22mg·g-1/58.64mg·g-1) and S (378.33mg·g-1/335.40mg.g-1) in the broad-leaved Korean pine mixed forests and the secondary poplar-birch forests, but above88.0%of the soil quantity focused in the stable fractions, which leaded to C allocation proportion in the stable fraction in the two forest types was72.7%and66.5%respectively. These data showed that soil organic C was mainly intercepted in the stable fractions. The mechanism of carbon is conductive for carbon accumulation over a long period, which was leaded by high mass fraction of stable fraction. On the contrary, the sum of mass fractions of liable fractions was only12%in the broad-leaved Korean pine mixed forests, but nitrogen contents in the liable fractions of P (37.19mg.g-1), EO (11.76mg·g-1) and S (10.27mg·g-1) were4-37times higher than those in the stable fractions of SA (313mg·g-1) and AI (1.06mg·g-1), which leaded N allocation proportion of liable fraction was53.3%.These data showed that soil nitrogen was allocated in the stable fractions and liable fractions fairly in the broad-leaved Korean pine mixed forests. This mechanism of N was conductive to supply quickly for soil fertility and at the same time also had the persistence. The sum of mass fractions of liable fractions was only11.7%in the secondary poplar-birch forests, but nitrogen contents in the liable fractions of P (78.58mg·g-1), EO (13.03mg·g-1) and S (38.47mg·g-1) were3-80times higher than those in the stable fractions of SA (3.53mg·g-1) and AI (0.88mg·g-1), which leaded N allocation proportion of liable fraction was59.1%; It become main body of soil N. These data showed that soil nitrogen was mainly distributed in liable fractions in the secondary poplar-birch forests. This mechanism of N was conductive to supply quickly for soil fertility of N.(2) The result of the infrared spectroscopy showed that there were highly significant positive linear relationships between functional groups of O-H stretching, N-H stretching, C-H stretching, O-H bending, C=O stretching, COO-stretching and soil C; Significant positive or highly positive linear relationships were found between functional groups of C-H stretching, O-H bending, C=O stretching and soil N, significant passive linear relationship between functional groups of C-O stretching,-COOH stretching, C-O stretching of polysaccharide and Si-O-Si stretching and soil N; A significant passive linear relationship was found between functional groups of O-H bending, C=O stretching and C/N, a significant highly positive linear relationship was found between functional groups of C-O stretching,-COOH stretching, C-O stretching of polysaccharide and Si-O-Si stretching and C/N. The above results suggested functional groups had the function of maintaining soil C and N and can reflect the chemical stability of soil fractions. It is of great ecological significance to research on soil C and N for the future.(3) The comparative analysis results of broad-leaved Korean pine mixed forests and secondary poplar-birch forests showed that there was similar feature on soil C and N for the kinds of forest types, but soil fractions C/N in the secondary poplar-birch forests were higher than that of the broad-leaved Korean pine mixed forests. This manifested that the former was not easier to break down; the later was easier to break down and supply fertility of N more quickly for stand growth. The result of X-ray diffraction (XRD) showed that more crystal was distributed in the stable fractions (SA, AI) and liable fractions (P) in the broad-leaved Korean pine forest, and the size of crystal grain in the stable fractions was larger than that of polar-birch forest. This helped understand the difference of soil carbon and nitrogen dynamic and their respond to future climate from the perspective of storage mechanism. Meanwhile, this provided the base for the change of C and N dynamic in the ecological succession process. |
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