Abstract:

The research was made that the change of component of soil humic substances in larch plantations and its effects on the soil acidity at the different development stages (young stand, half-mature stand, near mature stand, mature stand and young stand in the second rotation). The differences of soil organic matter content and the characteristics of component of humic substances between the larch plantations at different development stages and natural secondary forests, young stands in the first rotation and in the second rotation were compared. The results showed that soil organic matter content, the carbon content in humic acid and the carbon content in humin in rhizosphere and non_rhizosphere soil from young stand to near mature stand increased with stand ages grew; Soil organic matter content, the carbon content in fulvic acid and the carbon content in humin in rhizosphere and non-rhizosphere soil from near mature stand to mature stand decreased with stand ages grew; The humification degrees (the percentage of carbon content in humic acid in the total C) and the ratio of the carbon content in humic acid to the carbon content in fulvic acid in soil humic substances in the secondary forests were greater than those in the young stand and near mature stand. For the rhizosphere soil, the organic matter content, the carbon content in fulvic acid and the carbon content in humin decreased by 4.53%, 35.8% and 1.98% in young stand in the second rotation, respectively, as compared with those in young stand in the first rotation. For the non_rhizosphere soil, organic matter content, the carbon content in humic acid, the carbon content in fulvic acid and the carbon content in humin increased by 46.44%, 43.69%, 47.45% and 49.5% in young stand in the second rotation, respectively, as compared with those in young stand in the first rotation. The relationship between component of soil humic substances and soil acidity changed with stand ages changed. In rhizosphere soil, the close relationship existed among component of soil humic substances, soil active acidity (pH value), exchange acidity and hydrolytic acidity in various ages.

Key words: soil, larch plantations, component of humic substances, acidity