Morphological And Structural Characteristics Of Soil Fulvic Acids In The Natural Secondary Birch Forest And The Broad-leaved Korean Pine Mixed Forest In Xiaoxing’an Mountains

Fulvic acid (FA) is a very important component of soil humus show a strong effect in the process of the natural environment in a very wide range. FA not only affect the degradation rate of mineral ions in the soil, but also affect the physicochemical composition of colloidal articles in the aqueous environment, and which could control the operation of organic and inorganic contaminants effectively. The broad-leaved Korean Pine mixed forest is the top successional stage in Northeast Mountain, the natural secondary White Birch forest is the developing successional stage. Soils were collected from layer Al, B and C of the vertical profile in the natural secondary White Birch forest and the broad-leaved Korean Pine mixed forest from the Tieli Forest Bureau of Xiaoxing’an Mountain. The modified IHSS method for fine fractionation and purification was used to divide FA into four fractions:FA-1, FA-2, FA-3and FA-4. In this article, morphological and structural characteristics of FAs were analyzed by ATM and Py-GC/MS, and then compare the differences of FA fractions between the two forests. Our results were as follows:In the natural secondary White Birch forest, the content of soil organic matter, total N, P, K decreased gradually with the increasing soil depth, but the soil pH were opposite; the content of FA increased gradually with the increasing soil depth, and hydrophilic FAs (FA-1+FA-2) were much more than hydrophobic FAs (FA-3+FA-4); HA/FA decreased gradually with the increasing soil depth. Above indicators also showed a similar rule in the broad-leaved Korean Pine mixed forest, but there was a large differences in the content between two forests.FA fractions of different soil layers of the vertical profile in the natural secondary White Birch forest were observed by AFM. Molecules of FA fractions were various. Most of FA particles appear as a platy particle some were regular, such as round flake and oblong flake, which surface were smooth; others were irregular, such as aggregates make up by small particles, which surface were rough. Particle sizes of FA from FA-1to FA-4were increased generally except FA-4in Al layer and B layer. In three soil layers, there was no significant differences among hydrophilic FAs, but significant among hydrophobic FAs. But average particle sizes of hydrophobic FAs were increased with the soil depth in the broad-leaved Korean Pine mixed forest. These characteristics are evidently different with the particle sizes of FAs in the natural secondary White Birch forest.FA fractions of different soil layers of the vertical profile in the natural secondary White Birch forest were analyzed by Py-GC-MS. Pyrolysis products of FA fractions were identified including soil lipid compounds (alkane, alkene, fatty acid, ketone and alcohol), aromatic and polyaromatic compounds, methy ester compounds, N-compounds, phenol compounds, polysaccharides and Sulfur compounds. Relative contents of seven compounds of FA fractions showed that there was not any fractions contained all kinds of compounds, and contents of FA fractions were different. Factor analysis of FA compounds and FA fractions from different layers of the vertical profile showed that the factor scores of FA compounds and fractions were significantly different, but hydrophobic FAs or hydrophilic FAs were similar. FA was not a single homogeneous compound, but the structure of FA was very complex. Possible sources of FAs were very complicated, such as wax and suberin in plant roots and bark, and plant cellulose lignin microbial. The quality and activity of soil microbial were decreased with the soil depth, the decomposition degree of organic matter is also reduced. All of which resulted in significant differences in structures of FAs. Species of FA pyrolysis products in the broad-leaved Korean Pine mixed forest were similar with the natural secondary White Birch forest, but the quantity were more abundant than in the natural secondary White Birch forest. Material species of each FA compound contained was different. The degradation of soil microbial in the broad-leaved Korean Pine mixed forest were stronger than in the natural secondary Birch forest, then the FA morphology and structure in the broad-leaved Korean Pine mixed forest (the top succession stage) were more complicated than in the natural secondary Birch forest (the develop succession stage), to some extent, also the soil quality.